From 0c7fa090b0e9f4286282da0811139c9bc83ff983 Mon Sep 17 00:00:00 2001
From: Mattias Wadman <mattias.wadman@gmail.com>
Date: Sun, 15 Aug 2021 14:07:16 +0200
Subject: [PATCH] gojq: Initial update support

decode value give no updateable error
JQValue json value tries to replicate behaveior
---
 go.mod                                       |   2 +-
 go.sum                                       |   4 +-
 internal/gojqextra/gojqextra.go              | 136 ++++++++++++++++---
 pkg/interp/buffer.go                         |   4 +
 pkg/interp/interp.jq                         |   2 +-
 pkg/interp/testdata/value_array.fqtest       |  98 +++++++------
 pkg/interp/testdata/value_boolean.fqtest     | 114 +++++++---------
 pkg/interp/testdata/value_json_array.fqtest  | 121 +++++++++++++++++
 pkg/interp/testdata/value_json_object.fqtest | 111 +++++++++++++++
 pkg/interp/testdata/value_null.fqtest        | 110 +++++++--------
 pkg/interp/testdata/value_number.fqtest      | 110 +++++++--------
 pkg/interp/testdata/value_object.fqtest      | 108 +++++++--------
 pkg/interp/testdata/value_string.fqtest      | 100 +++++++-------
 pkg/interp/testdata/value_t.fqtest.tmpl      |  39 ++++++
 pkg/interp/testdata/value_t.fqtest.tmpl.sh   |  10 ++
 pkg/interp/testdata/value_type.fqtest.tmpl   |  41 ------
 pkg/interp/value.go                          |  18 +++
 17 files changed, 703 insertions(+), 425 deletions(-)
 create mode 100644 pkg/interp/testdata/value_json_array.fqtest
 create mode 100644 pkg/interp/testdata/value_json_object.fqtest
 create mode 100644 pkg/interp/testdata/value_t.fqtest.tmpl
 create mode 100644 pkg/interp/testdata/value_t.fqtest.tmpl.sh
 delete mode 100644 pkg/interp/testdata/value_type.fqtest.tmpl

diff --git a/go.mod b/go.mod
index a72cdcc8..6166e419 100644
--- a/go.mod
+++ b/go.mod
@@ -13,4 +13,4 @@ require (
 
 replace github.com/chzyer/readline => github.com/wader/readline v0.0.0-20210708114437-6e459499aaf5
 
-replace github.com/itchyny/gojq => github.com/wader/gojq v0.12.1-0.20210815085601-b5d8be28faea
+replace github.com/itchyny/gojq => github.com/wader/gojq v0.12.1-0.20210815133234-fa23c60d2da1
diff --git a/go.sum b/go.sum
index 0a5c321c..30570420 100644
--- a/go.sum
+++ b/go.sum
@@ -13,8 +13,8 @@ github.com/nbutton23/zxcvbn-go v0.0.0-20210217022336-fa2cb2858354/go.mod h1:KSVJ
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/testify v1.1.4/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
-github.com/wader/gojq v0.12.1-0.20210815085601-b5d8be28faea h1:n8MU47bCqWL/+U9MxhbMRUWe97txWtIAPsbyMMQrqfw=
-github.com/wader/gojq v0.12.1-0.20210815085601-b5d8be28faea/go.mod h1:EQUSKgW/YaOxmXpAwGiowFDO4i2Rmtk5+9dFyeiymAg=
+github.com/wader/gojq v0.12.1-0.20210815133234-fa23c60d2da1 h1:E51FeNldHd4SPpeBGuyu+LC0u/X/cagviC9Hk8eRY/o=
+github.com/wader/gojq v0.12.1-0.20210815133234-fa23c60d2da1/go.mod h1:EQUSKgW/YaOxmXpAwGiowFDO4i2Rmtk5+9dFyeiymAg=
 github.com/wader/readline v0.0.0-20210708114437-6e459499aaf5 h1:lNbk3zDwMc1TaNGWiKrSxCep6R8qqu9CGWBqSFD/9sE=
 github.com/wader/readline v0.0.0-20210708114437-6e459499aaf5/go.mod h1:1n88xxtpWULehIaVFcn5JQJy3RUe/5pvJznoiKWfKng=
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
diff --git a/internal/gojqextra/gojqextra.go b/internal/gojqextra/gojqextra.go
index 00f244df..889b7d54 100644
--- a/internal/gojqextra/gojqextra.go
+++ b/internal/gojqextra/gojqextra.go
@@ -69,15 +69,48 @@ func (err HasKeyTypeError) Error() string {
 	return "cannot check whether " + err.L + " has a key: " + err.R
 }
 
+type ArrayIndexTooLargeError struct {
+	V interface{}
+}
+
+func (err *ArrayIndexTooLargeError) Error() string {
+	return fmt.Sprintf("array index too large: %v", err.V)
+}
+
+func expectedArrayOrObject(key interface{}, typ string) error {
+	switch v := key.(type) {
+	case string:
+		return ExpectedObjectWithKeyError{Typ: typ, Key: v}
+	case int:
+		return ExpectedArrayWithIndexError{Typ: typ, Index: v}
+	default:
+		panic("unreachable")
+	}
+}
+
+type NonUpdatableTypeError struct {
+	Typ string
+	Key string
+}
+
+func (err NonUpdatableTypeError) Error() string {
+	return fmt.Sprintf("update key %v cannot be applied to: %s", err.Key, err.Typ)
+}
+
 // array
 
 var _ gojq.JQValue = Array{}
 
 type Array []interface{}
 
-func (v Array) JQValueLength() interface{}                  { return len(v) }
-func (v Array) JQValueSliceLen() interface{}                { return len(v) }
-func (v Array) JQValueIndex(index int) interface{}          { return v[index] }
+func (v Array) JQValueLength() interface{}   { return len(v) }
+func (v Array) JQValueSliceLen() interface{} { return len(v) }
+func (v Array) JQValueIndex(index int) interface{} {
+	if index < 0 {
+		return nil
+	}
+	return v[index]
+}
 func (v Array) JQValueSlice(start int, end int) interface{} { return v[start:end] }
 func (v Array) JQValueKey(name string) interface{} {
 	return ExpectedObjectError{Typ: "array"}
@@ -96,6 +129,44 @@ func (v Array) JQValueKeys() interface{} {
 	}
 	return vs
 }
+func (v Array) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	// TODO: handle {start:, end: }
+	// TODO: maybe should use gojq implementation as it's quite complex
+	intKey, ok := key.(int)
+	if !ok {
+		return HasKeyTypeError{L: "array", R: fmt.Sprintf("%v", key)}
+	}
+
+	if intKey > 0x3ffffff {
+		return ArrayIndexTooLargeError{V: intKey}
+	}
+
+	l := len(v)
+	if intKey >= l {
+		if delpath {
+			return v
+		}
+		l = intKey + 1
+	} else if intKey < -l {
+		if delpath {
+			return v
+		}
+		return FuncTypeError{Name: "setpath", Typ: "number"}
+	} else if intKey < 0 {
+		intKey += len(v)
+	}
+
+	var uu []interface{}
+	if delpath {
+		uu = append(v[0:intKey], v[intKey+1:]...)
+	} else {
+		uu = make([]interface{}, l)
+		copy(uu, v)
+		uu[intKey] = u
+	}
+
+	return uu
+}
 func (v Array) JQValueHas(key interface{}) interface{} {
 	intKey, ok := key.(int)
 	if !ok {
@@ -125,6 +196,24 @@ func (v Object) JQValueSlice(start int, end int) interface{} {
 	return ExpectedArrayError{Typ: "object"}
 }
 func (v Object) JQValueKey(name string) interface{} { return v[name] }
+func (v Object) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	stringKey, ok := key.(string)
+	if !ok {
+		return HasKeyTypeError{L: "object", R: fmt.Sprintf("%v", key)}
+	}
+
+	uu := make(map[string]interface{}, len(v))
+	for kv, vv := range v {
+		uu[kv] = vv
+	}
+	if delpath {
+		delete(uu, stringKey)
+	} else {
+		uu[stringKey] = u
+	}
+
+	return uu
+}
 func (v Object) JQValueEach() interface{} {
 	vs := make([]gojq.PathValue, len(v))
 	i := 0
@@ -175,8 +264,11 @@ func (v Number) JQValueSlice(start int, end int) interface{} {
 	return ExpectedArrayError{Typ: "number"}
 }
 func (v Number) JQValueKey(name string) interface{} { return ExpectedObjectError{Typ: "number"} }
-func (v Number) JQValueEach() interface{}           { return IteratorError{Typ: "number"} }
-func (v Number) JQValueKeys() interface{}           { return FuncTypeError{Name: "keys", Typ: "number"} }
+func (v Number) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	return expectedArrayOrObject(key, "number")
+}
+func (v Number) JQValueEach() interface{} { return IteratorError{Typ: "number"} }
+func (v Number) JQValueKeys() interface{} { return FuncTypeError{Name: "keys", Typ: "number"} }
 func (v Number) JQValueHas(key interface{}) interface{} {
 	return FuncTypeError{Name: "has", Typ: "number"}
 }
@@ -209,8 +301,11 @@ func (v String) JQValueIndex(index int) interface{} {
 }
 func (v String) JQValueSlice(start int, end int) interface{} { return string(v[start:end]) }
 func (v String) JQValueKey(name string) interface{}          { return ExpectedObjectError{Typ: "string"} }
-func (v String) JQValueEach() interface{}                    { return IteratorError{Typ: "string"} }
-func (v String) JQValueKeys() interface{}                    { return FuncTypeError{Name: "keys", Typ: "string"} }
+func (v String) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	return expectedArrayOrObject(key, "string")
+}
+func (v String) JQValueEach() interface{} { return IteratorError{Typ: "string"} }
+func (v String) JQValueKeys() interface{} { return FuncTypeError{Name: "keys", Typ: "string"} }
 func (v String) JQValueHas(key interface{}) interface{} {
 	return FuncTypeError{Name: "has", Typ: "string"}
 }
@@ -232,8 +327,11 @@ func (v Boolean) JQValueSlice(start int, end int) interface{} {
 	return ExpectedArrayError{Typ: "boolean"}
 }
 func (v Boolean) JQValueKey(name string) interface{} { return ExpectedObjectError{Typ: "boolean"} }
-func (v Boolean) JQValueEach() interface{}           { return IteratorError{Typ: "boolean"} }
-func (v Boolean) JQValueKeys() interface{}           { return FuncTypeError{Name: "keys", Typ: "boolean"} }
+func (v Boolean) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	return expectedArrayOrObject(key, "boolean")
+}
+func (v Boolean) JQValueEach() interface{} { return IteratorError{Typ: "boolean"} }
+func (v Boolean) JQValueKeys() interface{} { return FuncTypeError{Name: "keys", Typ: "boolean"} }
 func (v Boolean) JQValueHas(key interface{}) interface{} {
 	return FuncTypeError{Name: "has", Typ: "boolean"}
 }
@@ -260,13 +358,16 @@ func (v Null) JQValueSliceLen() interface{}                { return ExpectedArra
 func (v Null) JQValueIndex(index int) interface{}          { return ExpectedArrayError{Typ: "null"} }
 func (v Null) JQValueSlice(start int, end int) interface{} { return ExpectedArrayError{Typ: "null"} }
 func (v Null) JQValueKey(name string) interface{}          { return ExpectedObjectError{Typ: "null"} }
-func (v Null) JQValueEach() interface{}                    { return IteratorError{Typ: "null"} }
-func (v Null) JQValueKeys() interface{}                    { return FuncTypeError{Name: "keys", Typ: "null"} }
-func (v Null) JQValueHas(key interface{}) interface{}      { return FuncTypeError{Name: "has", Typ: "null"} }
-func (v Null) JQValueType() string                         { return "null" }
-func (v Null) JQValueToNumber() interface{}                { return FuncTypeError{Name: "tonumber", Typ: "null"} }
-func (v Null) JQValueToString() interface{}                { return "null" }
-func (v Null) JQValueToGoJQ() interface{}                  { return nil }
+func (v Null) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	return expectedArrayOrObject(key, "null")
+}
+func (v Null) JQValueEach() interface{}               { return IteratorError{Typ: "null"} }
+func (v Null) JQValueKeys() interface{}               { return FuncTypeError{Name: "keys", Typ: "null"} }
+func (v Null) JQValueHas(key interface{}) interface{} { return FuncTypeError{Name: "has", Typ: "null"} }
+func (v Null) JQValueType() string                    { return "null" }
+func (v Null) JQValueToNumber() interface{}           { return FuncTypeError{Name: "tonumber", Typ: "null"} }
+func (v Null) JQValueToString() interface{}           { return "null" }
+func (v Null) JQValueToGoJQ() interface{}             { return nil }
 
 // Base
 
@@ -285,6 +386,9 @@ func (v Base) JQValueSlice(start int, end int) interface{} { return ExpectedArra
 func (v Base) JQValueKey(name string) interface{} {
 	return ExpectedObjectWithKeyError{Typ: v.Typ, Key: name}
 }
+func (v Base) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	return expectedArrayOrObject(key, v.Typ)
+}
 func (v Base) JQValueEach() interface{} { return IteratorError{Typ: v.Typ} }
 func (v Base) JQValueKeys() interface{} { return FuncTypeError{Name: "keys", Typ: v.Typ} }
 func (v Base) JQValueHas(key interface{}) interface{} {
diff --git a/pkg/interp/buffer.go b/pkg/interp/buffer.go
index 4e2e8a17..55772f8e 100644
--- a/pkg/interp/buffer.go
+++ b/pkg/interp/buffer.go
@@ -142,6 +142,10 @@ func (bo bufferObject) JQValueToGoJQ() interface{} {
 	return buf.String()
 }
 
+func (bo bufferObject) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	return notUpdateableError{Key: fmt.Sprintf("%v", key), Typ: "buffer"}
+}
+
 func (bo bufferObject) Display(w io.Writer, opts Options) error {
 	if opts.Raw {
 		if _, err := io.Copy(w, bo.bbr.bb.Copy()); err != nil {
diff --git a/pkg/interp/interp.jq b/pkg/interp/interp.jq
index 394baf3d..2bdeb0ff 100644
--- a/pkg/interp/interp.jq
+++ b/pkg/interp/interp.jq
@@ -124,7 +124,7 @@ def _prompt:
   def _path_prefix:
     (._path? // []) | if . == [] then "" else path_to_expr + " " end;
   def _preview:
-    if type != "array" then
+    if (._format? // false) or type != "array" then
       _type_name_error
     else
       ( "["
diff --git a/pkg/interp/testdata/value_array.fqtest b/pkg/interp/testdata/value_array.fqtest
index 09f9b94a..d4ee6d0c 100644
--- a/pkg/interp/testdata/value_array.fqtest
+++ b/pkg/interp/testdata/value_array.fqtest
@@ -1,6 +1,6 @@
 /test.mp3:
-# display
-$ fq -d mp3 '.headers | ., tovalue, type, length?' /test.mp3
+$ fq -i -d mp3 . /test.mp3
+mp3> .headers | ., tovalue, type, length?
     |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |.headers: [1]
 0x00|49 44 33 04 00 00 00 00 00 23 54 53 53 45 00 00|ID3......#TSSE..|  [0]: {} (id3v2)
 *   |until 0x2c.7 (45)                              |                |
@@ -42,8 +42,7 @@ $ fq -d mp3 '.headers | ., tovalue, type, length?' /test.mp3
 ]
 "array"
 1
-# index
-$ fq -d mp3 '.headers[0] | ., type, length?' /test.mp3
+mp3> .headers[0] | ., type, length?
     |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |.headers[0]: {} (id3v2)
 0x00|49 44 33                                       |ID3             |  magic: "ID3" (Correct)
 0x00|         04                                    |   .            |  version: 4
@@ -56,24 +55,23 @@ $ fq -d mp3 '.headers[0] | ., type, length?' /test.mp3
 0x20|         00 00 00 00 00 00 00 00 00 00         |   ..........   |  padding: Correct (none) (zero padding)
 "object"
 7
-$ fq -d mp3 '.headers[-1000] | ., type, length?' /test.mp3
+mp3> .headers[-1000] | ., type, length?
 null
 "null"
 0
-$ fq -d mp3 '.headers[1000] | ., type, length?' /test.mp3
+mp3> .headers[1000] | ., type, length?
 null
 "null"
 0
-# slice
-$ fq -d mp3 '.headers[1:3] | ., type, length?' /test.mp3
+mp3> .headers[1:3] | ., type, length?
 []
 "array"
 0
-$ fq -d mp3 '.headers[0:-1] | ., type, length?' /test.mp3
+mp3> .headers[0:-1] | ., type, length?
 []
 "array"
 0
-$ fq -d mp3 '.headers[-1000:2000] | ., type, length?' /test.mp3
+mp3> .headers[-1000:2000] | ., type, length?
 [
   {
     "flags": {
@@ -112,96 +110,92 @@ $ fq -d mp3 '.headers[-1000:2000] | ., type, length?' /test.mp3
 ]
 "array"
 1
-# key
-$ fq -d mp3 '.headers["test"] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers["test"] | ., type, length?
 error: expected an object with key "test" but got: array
-# each
-$ fq -d mp3 '[.headers[]] | type, length?' /test.mp3
+mp3> [.headers[]] | type, length?
 "array"
 1
-# keys
-$ fq -d mp3 '.headers | keys' /test.mp3
+mp3> .headers | keys
 [
   0
 ]
-# has
-$ fq -d mp3 '.headers | has("a")' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers | has("a")
 error: cannot check whether array has a key: a
-$ fq -d mp3 '.headers | has(0)' /test.mp3
+mp3> .headers | has(0)
 true
-# type
-$ fq -d mp3 '.headers | type' /test.mp3
+mp3> .headers | type
 "array"
-# tonumber
-$ fq -d mp3 '.headers | tonumber' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers | tonumber
 error: tonumber cannot be applied to: array
-# tostring
-$ fq -d mp3 '.headers | tostring' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers | tostring
 error: tostring cannot be applied to: array
-# to gojq
-$ fq -d mp3 '.headers + ""' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers + ""
 error: cannot add: array ([{"flags":{"experimental_ ...]) and string ("")
-$ fq -d mp3 '.headers + 1' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers + 1
 error: cannot add: array ([{"flags":{"experimental_ ...]) and number (1)
-# test _keys
-$ fq -d mp3 '.headers._start | ., type, length?' /test.mp3
+mp3> .headers._start | ., type, length?
 0
 "number"
 0
-$ fq -d mp3 '.headers._stop | ., type, length?' /test.mp3
+mp3> .headers._stop | ., type, length?
 360
 "number"
 360
-$ fq -d mp3 '.headers._len | ., type, length?' /test.mp3
+mp3> .headers._len | ., type, length?
 360
 "number"
 360
-$ fq -d mp3 '.headers._name | ., type, length?' /test.mp3
+mp3> .headers._name | ., type, length?
 "headers"
 "string"
 7
-$ fq -d mp3 '.headers._symbol | ., type, length?' /test.mp3
+mp3> .headers._symbol | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers._description | ., type, length?' /test.mp3
+mp3> .headers._description | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers._path | ., type, length?' /test.mp3
+mp3> .headers._path | ., type, length?
 [
   "headers"
 ]
 "array"
 1
-$ fq -d mp3 '.headers._bits | ., type, length?' /test.mp3
+mp3> .headers._bits | ., type, length?
     |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x00|49 44 33 04 00 00 00 00 00 23 54 53 53 45 00 00|ID3......#TSSE..|
 <360 bits>
 "buffer"
 360
-$ fq -d mp3 '.headers._bytes | ., type, length?' /test.mp3
+mp3> .headers._bytes | ., type, length?
     |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x00|49 44 33 04 00 00 00 00 00 23 54 53 53 45 00 00|ID3......#TSSE..|
 <45 bytes>
 "buffer"
 45
-$ fq -d mp3 '.headers._error | ., type, length?' /test.mp3
+mp3> .headers._error | ., type, length?
 null
 "null"
 0
-$ fq -d mp3 '.headers._unknown | ., type, length?' /test.mp3
+mp3> .headers._unknown | ., type, length?
 false
 "boolean"
+mp3> .headers.a = 1
+error: cannot update key a for array
+mp3> .headers[0] = 1
+error: cannot update key 0 for array
+mp3> .headers.a |= empty
+error: expected an object with key "a" but got: array
+mp3> .headers[0] |= empty
+error: cannot update key 0 for array
+mp3> .headers | setpath(["a"]; 1)
+error: cannot update key a for array
+mp3> .headers | setpath([0]; 1)
+error: cannot update key 0 for array
+mp3> .headers | delpaths([["a"]])
+error: cannot update key a for array
+mp3> .headers | delpaths([[0]])
+error: cannot update key 0 for array
+mp3> ^D
diff --git a/pkg/interp/testdata/value_boolean.fqtest b/pkg/interp/testdata/value_boolean.fqtest
index ba11dd34..b20d4c77 100644
--- a/pkg/interp/testdata/value_boolean.fqtest
+++ b/pkg/interp/testdata/value_boolean.fqtest
@@ -1,106 +1,67 @@
 /test.mp3:
-# display
-$ fq -d mp3 '.headers[0].flags.unsynchronisation | ., tovalue, type, length?' /test.mp3
+$ fq -i -d mp3 . /test.mp3
+mp3> .headers[0].flags.unsynchronisation | ., tovalue, type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|               00                              |     .          |.headers[0].flags.unsynchronisation: false
 false
 "boolean"
-# index
-$ fq -d mp3 '.headers[0].flags.unsynchronisation[0] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation[0] | ., type, length?
 error: expected an array but got: boolean
-$ fq -d mp3 '.headers[0].flags.unsynchronisation[-1000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation[-1000] | ., type, length?
 error: expected an array but got: boolean
-$ fq -d mp3 '.headers[0].flags.unsynchronisation[1000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation[1000] | ., type, length?
 error: expected an array but got: boolean
-# slice
-$ fq -d mp3 '.headers[0].flags.unsynchronisation[1:3] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation[1:3] | ., type, length?
 error: expected an array but got: boolean
-$ fq -d mp3 '.headers[0].flags.unsynchronisation[0:-1] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation[0:-1] | ., type, length?
 error: expected an array but got: boolean
-$ fq -d mp3 '.headers[0].flags.unsynchronisation[-1000:2000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation[-1000:2000] | ., type, length?
 error: expected an array but got: boolean
-# key
-$ fq -d mp3 '.headers[0].flags.unsynchronisation["test"] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation["test"] | ., type, length?
 error: expected an object but got: boolean
-# each
-$ fq -d mp3 '[.headers[0].flags.unsynchronisation[]] | type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> [.headers[0].flags.unsynchronisation[]] | type, length?
 error: cannot iterate over: boolean
-# keys
-$ fq -d mp3 '.headers[0].flags.unsynchronisation | keys' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation | keys
 error: keys cannot be applied to: boolean
-# has
-$ fq -d mp3 '.headers[0].flags.unsynchronisation | has("a")' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation | has("a")
 error: has cannot be applied to: boolean
-$ fq -d mp3 '.headers[0].flags.unsynchronisation | has(0)' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation | has(0)
 error: has cannot be applied to: boolean
-# type
-$ fq -d mp3 '.headers[0].flags.unsynchronisation | type' /test.mp3
+mp3> .headers[0].flags.unsynchronisation | type
 "boolean"
-# tonumber
-$ fq -d mp3 '.headers[0].flags.unsynchronisation | tonumber' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation | tonumber
 error: tonumber cannot be applied to: boolean
-# tostring
-$ fq -d mp3 '.headers[0].flags.unsynchronisation | tostring' /test.mp3
+mp3> .headers[0].flags.unsynchronisation | tostring
 "false"
-# to gojq
-$ fq -d mp3 '.headers[0].flags.unsynchronisation + ""' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation + ""
 error: cannot add: boolean (false) and string ("")
-$ fq -d mp3 '.headers[0].flags.unsynchronisation + 1' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags.unsynchronisation + 1
 error: cannot add: boolean (false) and number (1)
-# test _keys
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._start | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._start | ., type, length?
 40
 "number"
 40
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._stop | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._stop | ., type, length?
 41
 "number"
 41
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._len | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._len | ., type, length?
 1
 "number"
 1
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._name | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._name | ., type, length?
 "unsynchronisation"
 "string"
 17
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._symbol | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._symbol | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._description | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._description | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._path | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._path | ., type, length?
 [
   "headers",
   0,
@@ -109,22 +70,39 @@ $ fq -d mp3 '.headers[0].flags.unsynchronisation._path | ., type, length?' /test
 ]
 "array"
 4
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._bits | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._bits | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|00                                             |.               |
 <1 bits>
 "buffer"
 1
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._bytes | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._bytes | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|00                                             |.               |
 <0 bytes>
 "buffer"
 0
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._error | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._error | ., type, length?
 null
 "null"
 0
-$ fq -d mp3 '.headers[0].flags.unsynchronisation._unknown | ., type, length?' /test.mp3
+mp3> .headers[0].flags.unsynchronisation._unknown | ., type, length?
 false
 "boolean"
+mp3> .headers[0].flags.unsynchronisation.a = 1
+error: expected an object but got: boolean
+mp3> .headers[0].flags.unsynchronisation[0] = 1
+error: expected an array but got: boolean
+mp3> .headers[0].flags.unsynchronisation.a |= empty
+error: expected an object but got: boolean
+mp3> .headers[0].flags.unsynchronisation[0] |= empty
+error: expected an array but got: boolean
+mp3> .headers[0].flags.unsynchronisation | setpath(["a"]; 1)
+error: expected an object with key "a" but got: boolean
+mp3> .headers[0].flags.unsynchronisation | setpath([0]; 1)
+error: expected an array with index 0 but got: boolean
+mp3> .headers[0].flags.unsynchronisation | delpaths([["a"]])
+error: expected an object with key "a" but got: boolean
+mp3> .headers[0].flags.unsynchronisation | delpaths([[0]])
+error: expected an array with index 0 but got: boolean
+mp3> ^D
diff --git a/pkg/interp/testdata/value_json_array.fqtest b/pkg/interp/testdata/value_json_array.fqtest
new file mode 100644
index 00000000..9bfe5de5
--- /dev/null
+++ b/pkg/interp/testdata/value_json_array.fqtest
@@ -0,0 +1,121 @@
+/test.mp3:
+$ fq -i -n '"[]" | json'
+json> (.) | ., tovalue, type, length?
+   |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
+   |                                               |                |.: [0] unnamed (json)
+[]
+"array"
+0
+json> (.)[0] | ., type, length?
+null
+"null"
+0
+json> (.)[-1000] | ., type, length?
+null
+"null"
+0
+json> (.)[1000] | ., type, length?
+null
+"null"
+0
+json> (.)[1:3] | ., type, length?
+[]
+"array"
+0
+json> (.)[0:-1] | ., type, length?
+[]
+"array"
+0
+json> (.)[-1000:2000] | ., type, length?
+[]
+"array"
+0
+json> (.)["test"] | ., type, length?
+error: expected an object but got: array
+json> [(.)[]] | type, length?
+"array"
+0
+json> (.) | keys
+[]
+json> (.) | has("a")
+error: cannot check whether array has a key: a
+json> (.) | has(0)
+false
+json> (.) | type
+"array"
+json> (.) | tonumber
+error: tonumber cannot be applied to: array
+json> (.) | tostring
+error: tostring cannot be applied to: array
+json> (.) + ""
+error: cannot add: array ([]) and string ("")
+json> (.) + 1
+error: cannot add: array ([]) and number (1)
+json> (.)._start | ., type, length?
+0
+"number"
+0
+json> (.)._stop | ., type, length?
+16
+"number"
+16
+json> (.)._len | ., type, length?
+16
+"number"
+16
+json> (.)._name | ., type, length?
+""
+"string"
+0
+json> (.)._symbol | ., type, length?
+""
+"string"
+0
+json> (.)._description | ., type, length?
+"unnamed"
+"string"
+7
+json> (.)._path | ., type, length?
+[]
+"array"
+0
+json> (.)._bits | ., type, length?
+   |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
+0x0|5b 5d                                          |[]              |
+<16 bits>
+"buffer"
+16
+json> (.)._bytes | ., type, length?
+   |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
+0x0|5b 5d                                          |[]              |
+<2 bytes>
+"buffer"
+2
+json> (.)._error | ., type, length?
+null
+"null"
+0
+json> (.)._unknown | ., type, length?
+false
+"boolean"
+json> (.).a = 1
+error: expected an object but got: array
+json> (.)[0] = 1
+[
+  1
+]
+json> (.).a |= empty
+error: expected an object but got: array
+json> (.)[0] |= empty
+[]
+json> (.) | setpath(["a"]; 1)
+error: cannot check whether array has a key: a
+json> (.) | setpath([0]; 1)
+[
+  1
+]
+json> (.) | delpaths([["a"]])
+error: cannot check whether array has a key: a
+json> (.) | delpaths([[0]])
+[]
+json> ^D
diff --git a/pkg/interp/testdata/value_json_object.fqtest b/pkg/interp/testdata/value_json_object.fqtest
new file mode 100644
index 00000000..f5a5c149
--- /dev/null
+++ b/pkg/interp/testdata/value_json_object.fqtest
@@ -0,0 +1,111 @@
+/test.mp3:
+$ fq -i -n '"{}" | json'
+json> (.) | ., tovalue, type, length?
+   |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
+   |                                               |                |.: {} unnamed (json)
+{}
+"object"
+0
+json> (.)[0] | ., type, length?
+error: expected an array but got: object
+json> (.)[-1000] | ., type, length?
+error: expected an array but got: object
+json> (.)[1000] | ., type, length?
+error: expected an array but got: object
+json> (.)[1:3] | ., type, length?
+error: expected an array but got: object
+json> (.)[0:-1] | ., type, length?
+error: expected an array but got: object
+json> (.)[-1000:2000] | ., type, length?
+error: expected an array but got: object
+json> (.)["test"] | ., type, length?
+null
+"null"
+0
+json> [(.)[]] | type, length?
+"array"
+0
+json> (.) | keys
+[]
+json> (.) | has("a")
+false
+json> (.) | has(0)
+error: cannot check whether object has a key: 0
+json> (.) | type
+"object"
+json> (.) | tonumber
+error: tonumber cannot be applied to: object
+json> (.) | tostring
+error: tostring cannot be applied to: object
+json> (.) + ""
+error: cannot add: object ({}) and string ("")
+json> (.) + 1
+error: cannot add: object ({}) and number (1)
+json> (.)._start | ., type, length?
+0
+"number"
+0
+json> (.)._stop | ., type, length?
+16
+"number"
+16
+json> (.)._len | ., type, length?
+16
+"number"
+16
+json> (.)._name | ., type, length?
+""
+"string"
+0
+json> (.)._symbol | ., type, length?
+""
+"string"
+0
+json> (.)._description | ., type, length?
+"unnamed"
+"string"
+7
+json> (.)._path | ., type, length?
+[]
+"array"
+0
+json> (.)._bits | ., type, length?
+   |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
+0x0|7b 7d                                          |{}              |
+<16 bits>
+"buffer"
+16
+json> (.)._bytes | ., type, length?
+   |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
+0x0|7b 7d                                          |{}              |
+<2 bytes>
+"buffer"
+2
+json> (.)._error | ., type, length?
+null
+"null"
+0
+json> (.)._unknown | ., type, length?
+false
+"boolean"
+json> (.).a = 1
+{
+  "a": 1
+}
+json> (.)[0] = 1
+error: expected an array but got: object
+json> (.).a |= empty
+{}
+json> (.)[0] |= empty
+error: expected an array but got: object
+json> (.) | setpath(["a"]; 1)
+{
+  "a": 1
+}
+json> (.) | setpath([0]; 1)
+error: cannot check whether object has a key: 0
+json> (.) | delpaths([["a"]])
+{}
+json> (.) | delpaths([[0]])
+error: cannot check whether object has a key: 0
+json> ^D
diff --git a/pkg/interp/testdata/value_null.fqtest b/pkg/interp/testdata/value_null.fqtest
index ee61a9ed..41c47dcc 100644
--- a/pkg/interp/testdata/value_null.fqtest
+++ b/pkg/interp/testdata/value_null.fqtest
@@ -1,103 +1,68 @@
 /test.mp3:
-# display
-$ fq -d mp3 '.headers[0].padding | ., tovalue, type, length?' /test.mp3
+$ fq -i -d mp3 . /test.mp3
+mp3> .headers[0].padding | ., tovalue, type, length?
     |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x20|         00 00 00 00 00 00 00 00 00 00         |   ..........   |.headers[0].padding: Correct (none) (zero padding)
 null
 "null"
 0
-# index
-$ fq -d mp3 '.headers[0].padding[0] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding[0] | ., type, length?
 error: expected an array but got: null
-$ fq -d mp3 '.headers[0].padding[-1000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding[-1000] | ., type, length?
 error: expected an array but got: null
-$ fq -d mp3 '.headers[0].padding[1000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding[1000] | ., type, length?
 error: expected an array but got: null
-# slice
-$ fq -d mp3 '.headers[0].padding[1:3] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding[1:3] | ., type, length?
 error: expected an array but got: null
-$ fq -d mp3 '.headers[0].padding[0:-1] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding[0:-1] | ., type, length?
 error: expected an array but got: null
-$ fq -d mp3 '.headers[0].padding[-1000:2000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding[-1000:2000] | ., type, length?
 error: expected an array but got: null
-# key
-$ fq -d mp3 '.headers[0].padding["test"] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding["test"] | ., type, length?
 error: expected an object but got: null
-# each
-$ fq -d mp3 '[.headers[0].padding[]] | type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> [.headers[0].padding[]] | type, length?
 error: cannot iterate over: null
-# keys
-$ fq -d mp3 '.headers[0].padding | keys' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding | keys
 error: keys cannot be applied to: null
-# has
-$ fq -d mp3 '.headers[0].padding | has("a")' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding | has("a")
 error: has cannot be applied to: null
-$ fq -d mp3 '.headers[0].padding | has(0)' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding | has(0)
 error: has cannot be applied to: null
-# type
-$ fq -d mp3 '.headers[0].padding | type' /test.mp3
+mp3> .headers[0].padding | type
 "null"
-# tonumber
-$ fq -d mp3 '.headers[0].padding | tonumber' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].padding | tonumber
 error: tonumber cannot be applied to: null
-# tostring
-$ fq -d mp3 '.headers[0].padding | tostring' /test.mp3
+mp3> .headers[0].padding | tostring
 "null"
-# to gojq
-$ fq -d mp3 '.headers[0].padding + ""' /test.mp3
+mp3> .headers[0].padding + ""
 ""
-$ fq -d mp3 '.headers[0].padding + 1' /test.mp3
+mp3> .headers[0].padding + 1
 1
-# test _keys
-$ fq -d mp3 '.headers[0].padding._start | ., type, length?' /test.mp3
+mp3> .headers[0].padding._start | ., type, length?
 280
 "number"
 280
-$ fq -d mp3 '.headers[0].padding._stop | ., type, length?' /test.mp3
+mp3> .headers[0].padding._stop | ., type, length?
 360
 "number"
 360
-$ fq -d mp3 '.headers[0].padding._len | ., type, length?' /test.mp3
+mp3> .headers[0].padding._len | ., type, length?
 80
 "number"
 80
-$ fq -d mp3 '.headers[0].padding._name | ., type, length?' /test.mp3
+mp3> .headers[0].padding._name | ., type, length?
 "padding"
 "string"
 7
-$ fq -d mp3 '.headers[0].padding._symbol | ., type, length?' /test.mp3
+mp3> .headers[0].padding._symbol | ., type, length?
 "Correct"
 "string"
 7
-$ fq -d mp3 '.headers[0].padding._description | ., type, length?' /test.mp3
+mp3> .headers[0].padding._description | ., type, length?
 "zero padding"
 "string"
 12
-$ fq -d mp3 '.headers[0].padding._path | ., type, length?' /test.mp3
+mp3> .headers[0].padding._path | ., type, length?
 [
   "headers",
   0,
@@ -105,22 +70,39 @@ $ fq -d mp3 '.headers[0].padding._path | ., type, length?' /test.mp3
 ]
 "array"
 3
-$ fq -d mp3 '.headers[0].padding._bits | ., type, length?' /test.mp3
+mp3> .headers[0].padding._bits | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|00 00 00 00 00 00 00 00 00 00                  |..........      |
 <80 bits>
 "buffer"
 80
-$ fq -d mp3 '.headers[0].padding._bytes | ., type, length?' /test.mp3
+mp3> .headers[0].padding._bytes | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|00 00 00 00 00 00 00 00 00 00                  |..........      |
 <10 bytes>
 "buffer"
 10
-$ fq -d mp3 '.headers[0].padding._error | ., type, length?' /test.mp3
+mp3> .headers[0].padding._error | ., type, length?
 null
 "null"
 0
-$ fq -d mp3 '.headers[0].padding._unknown | ., type, length?' /test.mp3
+mp3> .headers[0].padding._unknown | ., type, length?
 false
 "boolean"
+mp3> .headers[0].padding.a = 1
+error: expected an object but got: null
+mp3> .headers[0].padding[0] = 1
+error: expected an array but got: null
+mp3> .headers[0].padding.a |= empty
+error: expected an object but got: null
+mp3> .headers[0].padding[0] |= empty
+error: expected an array but got: null
+mp3> .headers[0].padding | setpath(["a"]; 1)
+error: expected an object with key "a" but got: null
+mp3> .headers[0].padding | setpath([0]; 1)
+error: expected an array with index 0 but got: null
+mp3> .headers[0].padding | delpaths([["a"]])
+error: expected an object with key "a" but got: null
+mp3> .headers[0].padding | delpaths([[0]])
+error: expected an array with index 0 but got: null
+mp3> ^D
diff --git a/pkg/interp/testdata/value_number.fqtest b/pkg/interp/testdata/value_number.fqtest
index 4f3cc17c..ecef7746 100644
--- a/pkg/interp/testdata/value_number.fqtest
+++ b/pkg/interp/testdata/value_number.fqtest
@@ -1,103 +1,68 @@
 /test.mp3:
-# display
-$ fq -d mp3 '.headers[0].version | ., tovalue, type, length?' /test.mp3
+$ fq -i -d mp3 . /test.mp3
+mp3> .headers[0].version | ., tovalue, type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|         04                                    |   .            |.headers[0].version: 4
 4
 "number"
 4
-# index
-$ fq -d mp3 '.headers[0].version[0] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version[0] | ., type, length?
 error: expected an array but got: number
-$ fq -d mp3 '.headers[0].version[-1000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version[-1000] | ., type, length?
 error: expected an array but got: number
-$ fq -d mp3 '.headers[0].version[1000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version[1000] | ., type, length?
 error: expected an array but got: number
-# slice
-$ fq -d mp3 '.headers[0].version[1:3] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version[1:3] | ., type, length?
 error: expected an array but got: number
-$ fq -d mp3 '.headers[0].version[0:-1] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version[0:-1] | ., type, length?
 error: expected an array but got: number
-$ fq -d mp3 '.headers[0].version[-1000:2000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version[-1000:2000] | ., type, length?
 error: expected an array but got: number
-# key
-$ fq -d mp3 '.headers[0].version["test"] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version["test"] | ., type, length?
 error: expected an object but got: number
-# each
-$ fq -d mp3 '[.headers[0].version[]] | type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> [.headers[0].version[]] | type, length?
 error: cannot iterate over: number
-# keys
-$ fq -d mp3 '.headers[0].version | keys' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version | keys
 error: keys cannot be applied to: number
-# has
-$ fq -d mp3 '.headers[0].version | has("a")' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version | has("a")
 error: has cannot be applied to: number
-$ fq -d mp3 '.headers[0].version | has(0)' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version | has(0)
 error: has cannot be applied to: number
-# type
-$ fq -d mp3 '.headers[0].version | type' /test.mp3
+mp3> .headers[0].version | type
 "number"
-# tonumber
-$ fq -d mp3 '.headers[0].version | tonumber' /test.mp3
+mp3> .headers[0].version | tonumber
 4
-# tostring
-$ fq -d mp3 '.headers[0].version | tostring' /test.mp3
+mp3> .headers[0].version | tostring
 "4"
-# to gojq
-$ fq -d mp3 '.headers[0].version + ""' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].version + ""
 error: cannot add: number (4) and string ("")
-$ fq -d mp3 '.headers[0].version + 1' /test.mp3
+mp3> .headers[0].version + 1
 5
-# test _keys
-$ fq -d mp3 '.headers[0].version._start | ., type, length?' /test.mp3
+mp3> .headers[0].version._start | ., type, length?
 24
 "number"
 24
-$ fq -d mp3 '.headers[0].version._stop | ., type, length?' /test.mp3
+mp3> .headers[0].version._stop | ., type, length?
 32
 "number"
 32
-$ fq -d mp3 '.headers[0].version._len | ., type, length?' /test.mp3
+mp3> .headers[0].version._len | ., type, length?
 8
 "number"
 8
-$ fq -d mp3 '.headers[0].version._name | ., type, length?' /test.mp3
+mp3> .headers[0].version._name | ., type, length?
 "version"
 "string"
 7
-$ fq -d mp3 '.headers[0].version._symbol | ., type, length?' /test.mp3
+mp3> .headers[0].version._symbol | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers[0].version._description | ., type, length?' /test.mp3
+mp3> .headers[0].version._description | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers[0].version._path | ., type, length?' /test.mp3
+mp3> .headers[0].version._path | ., type, length?
 [
   "headers",
   0,
@@ -105,22 +70,39 @@ $ fq -d mp3 '.headers[0].version._path | ., type, length?' /test.mp3
 ]
 "array"
 3
-$ fq -d mp3 '.headers[0].version._bits | ., type, length?' /test.mp3
+mp3> .headers[0].version._bits | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|04                                             |.               |
 <8 bits>
 "buffer"
 8
-$ fq -d mp3 '.headers[0].version._bytes | ., type, length?' /test.mp3
+mp3> .headers[0].version._bytes | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|04                                             |.               |
 <1 bytes>
 "buffer"
 1
-$ fq -d mp3 '.headers[0].version._error | ., type, length?' /test.mp3
+mp3> .headers[0].version._error | ., type, length?
 null
 "null"
 0
-$ fq -d mp3 '.headers[0].version._unknown | ., type, length?' /test.mp3
+mp3> .headers[0].version._unknown | ., type, length?
 false
 "boolean"
+mp3> .headers[0].version.a = 1
+error: expected an object but got: number
+mp3> .headers[0].version[0] = 1
+error: expected an array but got: number
+mp3> .headers[0].version.a |= empty
+error: expected an object but got: number
+mp3> .headers[0].version[0] |= empty
+error: expected an array but got: number
+mp3> .headers[0].version | setpath(["a"]; 1)
+error: expected an object with key "a" but got: number
+mp3> .headers[0].version | setpath([0]; 1)
+error: expected an array with index 0 but got: number
+mp3> .headers[0].version | delpaths([["a"]])
+error: expected an object with key "a" but got: number
+mp3> .headers[0].version | delpaths([[0]])
+error: expected an array with index 0 but got: number
+mp3> ^D
diff --git a/pkg/interp/testdata/value_object.fqtest b/pkg/interp/testdata/value_object.fqtest
index c129c036..753974dd 100644
--- a/pkg/interp/testdata/value_object.fqtest
+++ b/pkg/interp/testdata/value_object.fqtest
@@ -1,6 +1,6 @@
 /test.mp3:
-# display
-$ fq -d mp3 '.headers[0].flags | ., tovalue, type, length?' /test.mp3
+$ fq -i -d mp3 . /test.mp3
+mp3> .headers[0].flags | ., tovalue, type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |.headers[0].flags: {}
 0x0|               00                              |     .          |  unsynchronisation: false
 0x0|               00                              |     .          |  extended_header: false
@@ -14,104 +14,71 @@ $ fq -d mp3 '.headers[0].flags | ., tovalue, type, length?' /test.mp3
 }
 "object"
 4
-# index
-$ fq -d mp3 '.headers[0].flags[0] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags[0] | ., type, length?
 error: expected an array with index 0 but got: object
-$ fq -d mp3 '.headers[0].flags[-1000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags[-1000] | ., type, length?
 error: expected an array with index -2 but got: object
-$ fq -d mp3 '.headers[0].flags[1000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags[1000] | ., type, length?
 error: expected an array with index -1 but got: object
-# slice
-$ fq -d mp3 '.headers[0].flags[1:3] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags[1:3] | ., type, length?
 error: expected an array but got: object
-$ fq -d mp3 '.headers[0].flags[0:-1] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags[0:-1] | ., type, length?
 error: expected an array but got: object
-$ fq -d mp3 '.headers[0].flags[-1000:2000] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags[-1000:2000] | ., type, length?
 error: expected an array but got: object
-# key
-$ fq -d mp3 '.headers[0].flags["test"] | ., type, length?' /test.mp3
+mp3> .headers[0].flags["test"] | ., type, length?
 null
 "null"
 0
-# each
-$ fq -d mp3 '[.headers[0].flags[]] | type, length?' /test.mp3
+mp3> [.headers[0].flags[]] | type, length?
 "array"
 4
-# keys
-$ fq -d mp3 '.headers[0].flags | keys' /test.mp3
+mp3> .headers[0].flags | keys
 [
   "unsynchronisation",
   "extended_header",
   "experimental_indicator",
   "unused"
 ]
-# has
-$ fq -d mp3 '.headers[0].flags | has("a")' /test.mp3
+mp3> .headers[0].flags | has("a")
 false
-$ fq -d mp3 '.headers[0].flags | has(0)' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags | has(0)
 error: cannot check whether object has a key: 0
-# type
-$ fq -d mp3 '.headers[0].flags | type' /test.mp3
+mp3> .headers[0].flags | type
 "object"
-# tonumber
-$ fq -d mp3 '.headers[0].flags | tonumber' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags | tonumber
 error: tonumber cannot be applied to: object
-# tostring
-$ fq -d mp3 '.headers[0].flags | tostring' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags | tostring
 error: tostring cannot be applied to: object
-# to gojq
-$ fq -d mp3 '.headers[0].flags + ""' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags + ""
 error: cannot add: object ({"experimental_indicator" ...}) and string ("")
-$ fq -d mp3 '.headers[0].flags + 1' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].flags + 1
 error: cannot add: object ({"experimental_indicator" ...}) and number (1)
-# test _keys
-$ fq -d mp3 '.headers[0].flags._start | ., type, length?' /test.mp3
+mp3> .headers[0].flags._start | ., type, length?
 40
 "number"
 40
-$ fq -d mp3 '.headers[0].flags._stop | ., type, length?' /test.mp3
+mp3> .headers[0].flags._stop | ., type, length?
 48
 "number"
 48
-$ fq -d mp3 '.headers[0].flags._len | ., type, length?' /test.mp3
+mp3> .headers[0].flags._len | ., type, length?
 8
 "number"
 8
-$ fq -d mp3 '.headers[0].flags._name | ., type, length?' /test.mp3
+mp3> .headers[0].flags._name | ., type, length?
 "flags"
 "string"
 5
-$ fq -d mp3 '.headers[0].flags._symbol | ., type, length?' /test.mp3
+mp3> .headers[0].flags._symbol | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers[0].flags._description | ., type, length?' /test.mp3
+mp3> .headers[0].flags._description | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers[0].flags._path | ., type, length?' /test.mp3
+mp3> .headers[0].flags._path | ., type, length?
 [
   "headers",
   0,
@@ -119,22 +86,39 @@ $ fq -d mp3 '.headers[0].flags._path | ., type, length?' /test.mp3
 ]
 "array"
 3
-$ fq -d mp3 '.headers[0].flags._bits | ., type, length?' /test.mp3
+mp3> .headers[0].flags._bits | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|00                                             |.               |
 <8 bits>
 "buffer"
 8
-$ fq -d mp3 '.headers[0].flags._bytes | ., type, length?' /test.mp3
+mp3> .headers[0].flags._bytes | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|00                                             |.               |
 <1 bytes>
 "buffer"
 1
-$ fq -d mp3 '.headers[0].flags._error | ., type, length?' /test.mp3
+mp3> .headers[0].flags._error | ., type, length?
 null
 "null"
 0
-$ fq -d mp3 '.headers[0].flags._unknown | ., type, length?' /test.mp3
+mp3> .headers[0].flags._unknown | ., type, length?
 false
 "boolean"
+mp3> .headers[0].flags.a = 1
+error: cannot update key a for object
+mp3> .headers[0].flags[0] = 1
+error: expected an array with index 0 but got: object
+mp3> .headers[0].flags.a |= empty
+error: cannot update key a for object
+mp3> .headers[0].flags[0] |= empty
+error: expected an array with index 0 but got: object
+mp3> .headers[0].flags | setpath(["a"]; 1)
+error: cannot update key a for object
+mp3> .headers[0].flags | setpath([0]; 1)
+error: cannot update key 0 for object
+mp3> .headers[0].flags | delpaths([["a"]])
+error: cannot update key a for object
+mp3> .headers[0].flags | delpaths([[0]])
+error: cannot update key 0 for object
+mp3> ^D
diff --git a/pkg/interp/testdata/value_string.fqtest b/pkg/interp/testdata/value_string.fqtest
index cad87d63..da5005b5 100644
--- a/pkg/interp/testdata/value_string.fqtest
+++ b/pkg/interp/testdata/value_string.fqtest
@@ -1,105 +1,80 @@
 /test.mp3:
-# display
-$ fq -d mp3 '.headers[0].magic | ., tovalue, type, length?' /test.mp3
+$ fq -i -d mp3 . /test.mp3
+mp3> .headers[0].magic | ., tovalue, type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|49 44 33                                       |ID3             |.headers[0].magic: "ID3" (Correct)
 "ID3"
 "string"
 3
-# index
-$ fq -d mp3 '.headers[0].magic[0] | ., type, length?' /test.mp3
+mp3> .headers[0].magic[0] | ., type, length?
 "I"
 "string"
 1
-$ fq -d mp3 '.headers[0].magic[-1000] | ., type, length?' /test.mp3
+mp3> .headers[0].magic[-1000] | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers[0].magic[1000] | ., type, length?' /test.mp3
+mp3> .headers[0].magic[1000] | ., type, length?
 ""
 "string"
 0
-# slice
-$ fq -d mp3 '.headers[0].magic[1:3] | ., type, length?' /test.mp3
+mp3> .headers[0].magic[1:3] | ., type, length?
 "D3"
 "string"
 2
-$ fq -d mp3 '.headers[0].magic[0:-1] | ., type, length?' /test.mp3
+mp3> .headers[0].magic[0:-1] | ., type, length?
 "ID"
 "string"
 2
-$ fq -d mp3 '.headers[0].magic[-1000:2000] | ., type, length?' /test.mp3
+mp3> .headers[0].magic[-1000:2000] | ., type, length?
 "ID3"
 "string"
 3
-# key
-$ fq -d mp3 '.headers[0].magic["test"] | ., type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].magic["test"] | ., type, length?
 error: expected an object but got: string
-# each
-$ fq -d mp3 '[.headers[0].magic[]] | type, length?' /test.mp3
-exitcode: 5
-stderr:
+mp3> [.headers[0].magic[]] | type, length?
 error: cannot iterate over: string
-# keys
-$ fq -d mp3 '.headers[0].magic | keys' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].magic | keys
 error: keys cannot be applied to: string
-# has
-$ fq -d mp3 '.headers[0].magic | has("a")' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].magic | has("a")
 error: has cannot be applied to: string
-$ fq -d mp3 '.headers[0].magic | has(0)' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].magic | has(0)
 error: has cannot be applied to: string
-# type
-$ fq -d mp3 '.headers[0].magic | type' /test.mp3
+mp3> .headers[0].magic | type
 "string"
-# tonumber
-$ fq -d mp3 '.headers[0].magic | tonumber' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].magic | tonumber
 error: invalid number: "ID3"
-# tostring
-$ fq -d mp3 '.headers[0].magic | tostring' /test.mp3
+mp3> .headers[0].magic | tostring
 "ID3"
-# to gojq
-$ fq -d mp3 '.headers[0].magic + ""' /test.mp3
+mp3> .headers[0].magic + ""
 "ID3"
-$ fq -d mp3 '.headers[0].magic + 1' /test.mp3
-exitcode: 5
-stderr:
+mp3> .headers[0].magic + 1
 error: cannot add: string ("ID3") and number (1)
-# test _keys
-$ fq -d mp3 '.headers[0].magic._start | ., type, length?' /test.mp3
+mp3> .headers[0].magic._start | ., type, length?
 0
 "number"
 0
-$ fq -d mp3 '.headers[0].magic._stop | ., type, length?' /test.mp3
+mp3> .headers[0].magic._stop | ., type, length?
 24
 "number"
 24
-$ fq -d mp3 '.headers[0].magic._len | ., type, length?' /test.mp3
+mp3> .headers[0].magic._len | ., type, length?
 24
 "number"
 24
-$ fq -d mp3 '.headers[0].magic._name | ., type, length?' /test.mp3
+mp3> .headers[0].magic._name | ., type, length?
 "magic"
 "string"
 5
-$ fq -d mp3 '.headers[0].magic._symbol | ., type, length?' /test.mp3
+mp3> .headers[0].magic._symbol | ., type, length?
 ""
 "string"
 0
-$ fq -d mp3 '.headers[0].magic._description | ., type, length?' /test.mp3
+mp3> .headers[0].magic._description | ., type, length?
 "Correct"
 "string"
 7
-$ fq -d mp3 '.headers[0].magic._path | ., type, length?' /test.mp3
+mp3> .headers[0].magic._path | ., type, length?
 [
   "headers",
   0,
@@ -107,22 +82,39 @@ $ fq -d mp3 '.headers[0].magic._path | ., type, length?' /test.mp3
 ]
 "array"
 3
-$ fq -d mp3 '.headers[0].magic._bits | ., type, length?' /test.mp3
+mp3> .headers[0].magic._bits | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|49 44 33                                       |ID3             |
 <24 bits>
 "buffer"
 24
-$ fq -d mp3 '.headers[0].magic._bytes | ., type, length?' /test.mp3
+mp3> .headers[0].magic._bytes | ., type, length?
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|                |
 0x0|49 44 33                                       |ID3             |
 <3 bytes>
 "buffer"
 3
-$ fq -d mp3 '.headers[0].magic._error | ., type, length?' /test.mp3
+mp3> .headers[0].magic._error | ., type, length?
 null
 "null"
 0
-$ fq -d mp3 '.headers[0].magic._unknown | ., type, length?' /test.mp3
+mp3> .headers[0].magic._unknown | ., type, length?
 false
 "boolean"
+mp3> .headers[0].magic.a = 1
+error: expected an object but got: string
+mp3> .headers[0].magic[0] = 1
+error: expected an array with index 0 but got: string
+mp3> .headers[0].magic.a |= empty
+error: expected an object but got: string
+mp3> .headers[0].magic[0] |= empty
+error: expected an array with index 0 but got: string
+mp3> .headers[0].magic | setpath(["a"]; 1)
+error: expected an object with key "a" but got: string
+mp3> .headers[0].magic | setpath([0]; 1)
+error: expected an array with index 0 but got: string
+mp3> .headers[0].magic | delpaths([["a"]])
+error: expected an object with key "a" but got: string
+mp3> .headers[0].magic | delpaths([[0]])
+error: expected an array with index 0 but got: string
+mp3> ^D
diff --git a/pkg/interp/testdata/value_t.fqtest.tmpl b/pkg/interp/testdata/value_t.fqtest.tmpl
new file mode 100644
index 00000000..5259f3c1
--- /dev/null
+++ b/pkg/interp/testdata/value_t.fqtest.tmpl
@@ -0,0 +1,39 @@
+/test.mp3:
+$ CMD
+PROMPT> EXPR | ., tovalue, type, length?
+PROMPT> EXPR[0] | ., type, length?
+PROMPT> EXPR[-1000] | ., type, length?
+PROMPT> EXPR[1000] | ., type, length?
+PROMPT> EXPR[1:3] | ., type, length?
+PROMPT> EXPR[0:-1] | ., type, length?
+PROMPT> EXPR[-1000:2000] | ., type, length?
+PROMPT> EXPR["test"] | ., type, length?
+PROMPT> [EXPR[]] | type, length?
+PROMPT> EXPR | keys
+PROMPT> EXPR | has("a")
+PROMPT> EXPR | has(0)
+PROMPT> EXPR | type
+PROMPT> EXPR | tonumber
+PROMPT> EXPR | tostring
+PROMPT> EXPR + ""
+PROMPT> EXPR + 1
+PROMPT> EXPR._start | ., type, length?
+PROMPT> EXPR._stop | ., type, length?
+PROMPT> EXPR._len | ., type, length?
+PROMPT> EXPR._name | ., type, length?
+PROMPT> EXPR._symbol | ., type, length?
+PROMPT> EXPR._description | ., type, length?
+PROMPT> EXPR._path | ., type, length?
+PROMPT> EXPR._bits | ., type, length?
+PROMPT> EXPR._bytes | ., type, length?
+PROMPT> EXPR._error | ., type, length?
+PROMPT> EXPR._unknown | ., type, length?
+PROMPT> EXPR.a = 1
+PROMPT> EXPR[0] = 1
+PROMPT> EXPR.a |= empty
+PROMPT> EXPR[0] |= empty
+PROMPT> EXPR | setpath(["a"]; 1)
+PROMPT> EXPR | setpath([0]; 1)
+PROMPT> EXPR | delpaths([["a"]])
+PROMPT> EXPR | delpaths([[0]])
+PROMPT> ^D
\ No newline at end of file
diff --git a/pkg/interp/testdata/value_t.fqtest.tmpl.sh b/pkg/interp/testdata/value_t.fqtest.tmpl.sh
new file mode 100644
index 00000000..f18c63f2
--- /dev/null
+++ b/pkg/interp/testdata/value_t.fqtest.tmpl.sh
@@ -0,0 +1,10 @@
+#!/bin/sh
+sed 's/CMD/fq -i -d mp3 . \/test.mp3/g' <value_t.fqtest.tmpl | sed 's/EXPR/.headers/g' | sed 's/PROMPT/mp3/g' >value_array.fqtest
+sed 's/CMD/fq -i -d mp3 . \/test.mp3/g' <value_t.fqtest.tmpl | sed 's/EXPR/.headers[0].flags.unsynchronisation/g' | sed 's/PROMPT/mp3/g' >value_boolean.fqtest
+sed 's/CMD/fq -i -d mp3 . \/test.mp3/g' <value_t.fqtest.tmpl | sed 's/EXPR/.headers[0].padding/g' | sed 's/PROMPT/mp3/g' >value_null.fqtest
+sed 's/CMD/fq -i -d mp3 . \/test.mp3/g' <value_t.fqtest.tmpl | sed 's/EXPR/.headers[0].version/g' | sed 's/PROMPT/mp3/g' >value_number.fqtest
+sed 's/CMD/fq -i -d mp3 . \/test.mp3/g' <value_t.fqtest.tmpl | sed 's/EXPR/.headers[0].flags/g' | sed 's/PROMPT/mp3/g' >value_object.fqtest
+sed 's/CMD/fq -i -d mp3 . \/test.mp3/g' <value_t.fqtest.tmpl | sed 's/EXPR/.headers[0].magic/g' | sed 's/PROMPT/mp3/g' >value_string.fqtest
+
+sed "s/CMD/fq -i -n '\"[]\" | json'/g" <value_t.fqtest.tmpl | sed 's/EXPR/(.)/g' | sed 's/PROMPT/json/g' >value_json_array.fqtest
+sed "s/CMD/fq -i -n '\"{}\" | json'/g" <value_t.fqtest.tmpl | sed 's/EXPR/(.)/g' | sed 's/PROMPT/json/g' >value_json_object.fqtest
diff --git a/pkg/interp/testdata/value_type.fqtest.tmpl b/pkg/interp/testdata/value_type.fqtest.tmpl
deleted file mode 100644
index b13c2790..00000000
--- a/pkg/interp/testdata/value_type.fqtest.tmpl
+++ /dev/null
@@ -1,41 +0,0 @@
-/test.mp3:
-# display
-> fq -d mp3 'EXPR | ., tovalue, type, length?' /test.mp3
-# index
-> fq -d mp3 'EXPR[0] | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR[-1000] | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR[1000] | ., type, length?' /test.mp3
-# slice
-> fq -d mp3 'EXPR[1:3] | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR[0:-1] | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR[-1000:2000] | ., type, length?' /test.mp3
-# key
-> fq -d mp3 'EXPR["test"] | ., type, length?' /test.mp3
-# each
-> fq -d mp3 '[EXPR[]] | type, length?' /test.mp3
-# keys
-> fq -d mp3 'EXPR | keys' /test.mp3
-# has
-> fq -d mp3 'EXPR | has("a")' /test.mp3
-> fq -d mp3 'EXPR | has(0)' /test.mp3
-# type
-> fq -d mp3 'EXPR | type' /test.mp3
-# tonumber
-> fq -d mp3 'EXPR | tonumber' /test.mp3
-# tostring
-> fq -d mp3 'EXPR | tostring' /test.mp3
-# to gojq
-> fq -d mp3 'EXPR + ""' /test.mp3
-> fq -d mp3 'EXPR + 1' /test.mp3
-# test _keys
-> fq -d mp3 'EXPR._start | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._stop | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._len | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._name | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._symbol | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._description | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._path | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._bits | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._bytes | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._error | ., type, length?' /test.mp3
-> fq -d mp3 'EXPR._unknown | ., type, length?' /test.mp3
diff --git a/pkg/interp/value.go b/pkg/interp/value.go
index 6ce2aca1..b3d3f8c0 100644
--- a/pkg/interp/value.go
+++ b/pkg/interp/value.go
@@ -22,6 +22,15 @@ func (err expectedExtkeyError) Error() string {
 	return "expected a extkey but got: " + err.Key
 }
 
+type notUpdateableError struct {
+	Typ string
+	Key string
+}
+
+func (err notUpdateableError) Error() string {
+	return fmt.Sprintf("cannot update key %s for %s", err.Key, err.Typ)
+}
+
 // TODO: rename
 type valueIf interface {
 	InterpValue
@@ -249,6 +258,9 @@ func (v bufferDecodeValue) JQValueSlice(start int, end int) interface{} {
 	}
 	return b.String()
 }
+func (v bufferDecodeValue) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	return notUpdateableError{Key: fmt.Sprintf("%v", key), Typ: "string"}
+}
 func (v bufferDecodeValue) JQValueToNumber() interface{} {
 	s, ok := v.JQValueToString().(string)
 	if ok {
@@ -307,6 +319,9 @@ func (v arrayDecodeValue) JQValueSlice(start int, end int) interface{} {
 	}
 	return vs
 }
+func (v arrayDecodeValue) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	return notUpdateableError{Key: fmt.Sprintf("%v", key), Typ: "array"}
+}
 func (v arrayDecodeValue) JQValueEach() interface{} {
 	props := make([]gojq.PathValue, len(v.Array))
 	for i, f := range v.Array {
@@ -368,6 +383,9 @@ func (v structDecodeValue) JQValueKey(name string) interface{} {
 	}
 	return nil
 }
+func (v structDecodeValue) JQValueUpdate(key interface{}, u interface{}, delpath bool) interface{} {
+	return notUpdateableError{Key: fmt.Sprintf("%v", key), Typ: "object"}
+}
 func (v structDecodeValue) JQValueEach() interface{} {
 	props := make([]gojq.PathValue, len(v.Struct))
 	for i, f := range v.Struct {