@@ -6,7 +6,7 @@ module Ur.Deconstructor exposing
66 , int, signedInt, bigint
77 , float32, float64
88 , cord, tape
9− , bytes, sig, ignore, tar, lazy
9+ , bytes, sig, ignore, tar, lazy, debug
1010 )
1111
1212{-| This module provides an API to deconstruct `Noun`s into arbitrary Elm data structures.
@@ -55,7 +55,7 @@ You would parse a `[%edit @ cord]` like this:
5555
5656# Miscellaneous
5757
58−@docs bytes, sig, ignore, tar, lazy
58+@docs bytes, sig, ignore, tar, lazy, debug
5959
6060-}
6161
@@ -66,7 +66,7 @@ import Bytes exposing (Bytes, Endianness(..))
6666import Bytes.Decode as BD
6767import Bytes.Encode as BE
6868import Bytes.Extra
69−import Ur.Jam exposing (cue)
69+import Ur.Jam exposing (cue, isSig)
7070import Ur.Types exposing (..)
7171
7272
@@ -337,3 +337,42 @@ Always succeeds.
337337tar : Deconstructor Noun
338338tar =
339339 Just
340+
341+
342+{-| Debug a deconstructor.
343+If the deconstructor from the second argument fails then the failed nock will be printed to the console.
344+-}
345+debug : (String -> String) -> Deconstructor a -> Deconstructor a
346+debug log f noun =
347+ case f noun of
348+ Just x ->
349+ Just x
350+
351+ Nothing ->
352+ let
353+ _ =
354+ log (prettyNoun noun)
355+ in
356+ Nothing
357+
358+
359+prettyNoun : Noun -> String
360+prettyNoun noun =
361+ let
362+ go isRhs n =
363+ case n of
364+ Atom a ->
365+ if isSig a then
366+ "~"
367+
368+ else
369+ "@"
370+
371+ Cell ( lhs, rhs ) ->
372+ if isRhs then
373+ go False lhs ++ " " ++ go True rhs
374+
375+ else
376+ "[" ++ go False lhs ++ " " ++ go True rhs ++ "]"
377+ in
378+ go False noun