I have this dcg code: program([Node|Rest]) --> item(Node), (program(Rest) | {Rest = []}). item(Node) --> lit(Node) | quote(Node) | pat_obj(Node) | word(Node). %| word_def(Node). lit(num(N, L)) --> [lit(N, L)], {number(N)}. lit(str(S, L)) --> [lit(S, L)], {string(S)}. lit(true(L)) --> [word_s("t",…

[image] JosephOziel: ?- pparse("( |> )"). What is pparse/1? It’s difficult to help you if we can’t run your program. :slight_smile: If you don’t want backtracking, you can do something like this: item(Node) --> lit(Node), !. item(Node) --> quote(Node), !. item(Node) --> pat_obj(Node), !. it…

[image] JosephOziel: I want it to fail if it can’t match a pat_obj, not backtrack As a hint, the usual code for this is: !, fail. fail/0 means the same as false/0 - it just has slightly more relevant connotations in English.

I will try to figure out where to put this. Thanks

Hm. I added this clause to the ends of the pat clauses, and it still doesn’t want to fail pat(_) --> !, {fail}.

Hm. I added this clause to the ends of the pat clauses, and it still doesn’t want to fail pat(_) --> !, {fail}.? It seems for prolog it is persistent and finds one solution that works, and the next one fails. How can I make it so it would ONLY fail.

A Minimal reproducible example - Wikipedia would be nicer for people (e.g. me) to look at.

[image] brebs: A Minimal reproducible example This post has some other details of note. [image] Minimal and reproducible working examples Wiki How to create a Minimal, Reproducible Example When asking for help with code that is not working, people will be better ab…

Thank you for your help, I will try these out and let you know. For further context, here is the code for the lexer and parser currently (didn’t make your changes yet) Noise/frontend at main · JosephOziel/Noise Deque based concatenative language for MIDI music. - JosephOziel/Noise …

Preventing Backtracking with DCGs

Help!

EricGT May 1, 2024, 10:38am 7

This post has some other details of note.

Topic		Replies	Views
Controlling backtracking in a DCG grammar? Help!	10	1240	July 11, 2019
Adding error detection to DCG rules Algorithm	18	1924	May 7, 2020
DCG look ahead, how its done? General	47	509	August 13, 2024
Is there a preferred way to check for valid characters when using DCG? Help!	5	874	March 12, 2019
Go an exception when aborting DCG processing .. but is anyone interested in these? Tools bug	11	1197	July 6, 2020

Preventing Backtracking with DCGs

Related topics