I forgot reason why end_of_file is returned by ‘term_string’ for the null string. Is this widely accepted in Prolog community ? Certainly, it seems difficult to define a term for the string “” other than the end_of_file. ?- term_string("", R). R = "\"\"". % ?- term_string(A, ''). %@ A = end_of…

An error can give more information, such as where the syntax error was detected. And an error can be easily converted to failure, using catch/3.

Yes, but even better is to not have to jump through those hoops in the first place, when they don’t add significant benefit :wink:

[image] peter.ludemann: An error can give more information, such as where the syntax error was detected That could just be the same predicate with a different arity, to add a variable indicating syntax error and where. To be used when the program cares about such details. I suppose my point …

[image] brebs: shouldn’t exceptions be the last choice rather than the first choice, in Prolog? I suppose it boils down to whether you think a predicate is something that can either succeed (possibly multiple times) or fail; or is it a predicate that should always succeed (there are a few oth…

[image] brebs: Why not just simple failure of term_string(T, "") because there is no valid term. In the same way that e.g. between(4, 3, N) returns failure rather than an exception “3 is not in the domain of 4 or above” :grinning: Exceptions seem more awkward. Failure seems perfectly logical, n…

[image] Errors considered harmful Request For Comments Interesting discussion on Picat extensions and cuts and I’d like to add my own personal pet peeve with “standard” Prolog. I don’t think there would be much opposition to the topic title. After all (unhandled) errors r…

[image] brebs: I suppose my point boils down to: shouldn’t exceptions be the last choice rather than the first choice, in Prolog? That depends IMO. In this case, term_string/2 already raises a syntax error if the string is not valid Prolog syntax. That is, for larger terms, pretty usefu…

[image] jan: The current GIT version raises a syntax_error(end_of_string) exception. Thanks. As your analysis, syntax error is better than failure for this case because there might be possible serious error other than syntax error .

[image] jan: write failure driven loops processing a lot of strings. A failure will silently omit the invalid strings. Quiet unexpected failures are probably the biggest debugging problem I have in Prolog. Features such as SSU and the det/1 directive have helped a lot with that; which is why …

To hopefully make both camps content: how about adding a variant which has an additional options argument, so we could have: term_string(T, "a(", options([fail_silently])) This makes it explicit that the programmer is taking responsibility for the errors. The default would be to raise an exceptio…

`term_string/2` returns `end_of_file` with null string at the second arg

General

Boris April 28, 2024, 6:37am 12

the thread that @peter.ludemann meant, most probably

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`term_string/2` returns `end_of_file` with null string at the second arg

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