diff --git a/format/ar/ar.go b/format/ar/ar.go
index 33ef90c2..5be8c322 100644
--- a/format/ar/ar.go
+++ b/format/ar/ar.go
@@ -1,9 +1,6 @@
 package ar
 
 import (
-	"strconv"
-	"strings"
-
 	"github.com/wader/fq/format"
 	"github.com/wader/fq/format/registry"
 	"github.com/wader/fq/pkg/decode"
@@ -27,29 +24,14 @@ func init() {
 func decodeAr(d *decode.D, in interface{}) interface{} {
 	d.FieldUTF8("signature", 8, d.AssertStr("!<arch>\n"))
 	d.FieldArray("files", func(d *decode.D) {
-		// TODO: extract? share with tar?
-		mapStrToSymU := func(base int) scalar.Mapper {
-			return scalar.Fn(func(s scalar.S) (scalar.S, error) {
-				ts := strings.Trim(s.ActualStr(), " ")
-				if ts != "" {
-					n, err := strconv.ParseUint(ts, base, 64)
-					if err != nil {
-						return s, err
-					}
-					s.Sym = n
-				}
-				return s, nil
-			})
-		}
-
 		for !d.End() {
 			d.FieldStruct("file", func(d *decode.D) {
 				d.FieldUTF8("identifier", 16, scalar.TrimSpace)
-				d.FieldUTF8("modification_timestamp", 12, scalar.TrimSpace, mapStrToSymU(10))
-				d.FieldUTF8("owner_id", 6, scalar.TrimSpace, mapStrToSymU(10))
-				d.FieldUTF8("group_id", 6, scalar.TrimSpace, mapStrToSymU(10))
-				d.FieldUTF8("file_mode", 8, scalar.TrimSpace, mapStrToSymU(8)) // Octal
-				sizeS := d.FieldScalarUTF8("file_size", 10, scalar.TrimSpace, mapStrToSymU(10))
+				d.FieldUTF8("modification_timestamp", 12, scalar.TrimSpace, scalar.StrUintToSym(10))
+				d.FieldUTF8("owner_id", 6, scalar.TrimSpace, scalar.StrUintToSym(10))
+				d.FieldUTF8("group_id", 6, scalar.TrimSpace, scalar.StrUintToSym(10))
+				d.FieldUTF8("file_mode", 8, scalar.TrimSpace, scalar.StrUintToSym(8)) // Octal
+				sizeS := d.FieldScalarUTF8("file_size", 10, scalar.TrimSpace, scalar.StrUintToSym(10))
 				if sizeS.Sym == nil {
 					d.Fatalf("could not decode file_size")
 				}
diff --git a/format/tar/tar.go b/format/tar/tar.go
index b0fd55f6..f1ee766e 100644
--- a/format/tar/tar.go
+++ b/format/tar/tar.go
@@ -5,8 +5,6 @@ package tar
 
 import (
 	"bytes"
-	"strconv"
-	"strings"
 
 	"github.com/wader/fq/format"
 	"github.com/wader/fq/format/registry"
@@ -33,17 +31,6 @@ func tarDecode(d *decode.D, in interface{}) interface{} {
 	const blockBits = blockBytes * 8
 
 	mapTrimSpaceNull := scalar.Trim(" \x00")
-	mapOctStrToSymU := scalar.Fn(func(s scalar.S) (scalar.S, error) {
-		ts := strings.Trim(s.ActualStr(), " ")
-		if ts != "" {
-			n, err := strconv.ParseUint(ts, 8, 64)
-			if err != nil {
-				return s, err
-			}
-			s.Sym = n
-		}
-		return s, nil
-	})
 	blockPadding := func(d *decode.D) int64 {
 		return (blockBits - (d.Pos() % blockBits)) % blockBits
 	}
@@ -58,24 +45,24 @@ func tarDecode(d *decode.D, in interface{}) interface{} {
 		for !d.End() {
 			d.FieldStruct("file", func(d *decode.D) {
 				d.FieldUTF8("name", 100, mapTrimSpaceNull)
-				d.FieldUTF8NullFixedLen("mode", 8, mapOctStrToSymU)
-				d.FieldUTF8NullFixedLen("uid", 8, mapOctStrToSymU)
-				d.FieldUTF8NullFixedLen("gid", 8, mapOctStrToSymU)
-				sizeS := d.FieldScalarUTF8NullFixedLen("size", 12, mapOctStrToSymU)
+				d.FieldUTF8NullFixedLen("mode", 8, scalar.StrUintToSym(8))
+				d.FieldUTF8NullFixedLen("uid", 8, scalar.StrUintToSym(8))
+				d.FieldUTF8NullFixedLen("gid", 8, scalar.StrUintToSym(8))
+				sizeS := d.FieldScalarUTF8NullFixedLen("size", 12, scalar.StrUintToSym(8))
 				if sizeS.Sym == nil {
 					d.Fatalf("could not decode size")
 				}
 				size := int64(sizeS.SymU()) * 8
-				d.FieldUTF8NullFixedLen("mtime", 12, mapOctStrToSymU)
-				d.FieldUTF8NullFixedLen("chksum", 8, mapOctStrToSymU)
+				d.FieldUTF8NullFixedLen("mtime", 12, scalar.StrUintToSym(8))
+				d.FieldUTF8NullFixedLen("chksum", 8, scalar.StrUintToSym(8))
 				d.FieldUTF8("typeflag", 1, mapTrimSpaceNull)
 				d.FieldUTF8("linkname", 100, mapTrimSpaceNull)
 				d.FieldUTF8("magic", 6, mapTrimSpaceNull, d.AssertStr("ustar"))
-				d.FieldUTF8NullFixedLen("version", 2, mapOctStrToSymU)
+				d.FieldUTF8NullFixedLen("version", 2, scalar.StrUintToSym(8))
 				d.FieldUTF8("uname", 32, mapTrimSpaceNull)
 				d.FieldUTF8("gname", 32, mapTrimSpaceNull)
-				d.FieldUTF8NullFixedLen("devmajor", 8, mapOctStrToSymU)
-				d.FieldUTF8NullFixedLen("devminor", 8, mapOctStrToSymU)
+				d.FieldUTF8NullFixedLen("devmajor", 8, scalar.StrUintToSym(8))
+				d.FieldUTF8NullFixedLen("devminor", 8, scalar.StrUintToSym(8))
 				d.FieldUTF8("prefix", 155, mapTrimSpaceNull)
 				d.FieldRawLen("header_block_padding", blockPadding(d), d.BitBufIsZero())
 
diff --git a/pkg/scalar/scalar.go b/pkg/scalar/scalar.go
index 315a3a21..dd93521f 100644
--- a/pkg/scalar/scalar.go
+++ b/pkg/scalar/scalar.go
@@ -8,6 +8,7 @@ package scalar
 import (
 	"bytes"
 	"fmt"
+	"strconv"
 	"strings"
 
 	"github.com/wader/fq/pkg/bitio"
@@ -113,6 +114,32 @@ var TrimSpace = Fn(func(s S) (S, error) {
 	return s, nil
 })
 
+func strMapToSym(fn func(s string) (interface{}, error)) Mapper {
+	return Fn(func(s S) (S, error) {
+		ts := strings.TrimSpace(s.ActualStr())
+		if ts != "" {
+			n, err := fn(ts)
+			if err != nil {
+				return s, err
+			}
+			s.Sym = n
+		}
+		return s, nil
+	})
+}
+
+func StrUintToSym(base int) Mapper {
+	return strMapToSym(func(s string) (interface{}, error) { return strconv.ParseUint(s, base, 64) })
+}
+
+func StrIntToSym(base int) Mapper {
+	return strMapToSym(func(s string) (interface{}, error) { return strconv.ParseInt(s, base, 64) })
+}
+
+func StrFToSym(base int) Mapper {
+	return strMapToSym(func(s string) (interface{}, error) { return strconv.ParseFloat(s, base) })
+}
+
 //nolint:unparam
 func rawSym(s S, nBytes int, fn func(b []byte) string) (S, error) {
 	bb, ok := s.Actual.(*bitio.Buffer)