Coincidentally, I got annoyed at getting an exception from format/2 on incorrect “n placeholder”/“m arguments” matching if “n > m” and used this annoyance to look at what other systems are doing. [David Tonhofer] Can I make Prolog's "format/x" family behave leniently? prin…

While I have been following the thread at StackOverflow, perhaps you could add more details into your post for those here. When I read the details on StackOverflow it appeared to me you were looking for a change to the code or pointing out a bug that could be fixed. When I read your post here I get…

Typically format/3 takes a format and a fixed list of arguments that should match by type and length, If you are not sure about the type there is always ~w and similar generic write predicates that will always do the job. That is already a lot more relaxed than e.g., C where a wrong argument type…

Yup - almost every time where a format/{2,3} call was wrong, it manifested itself by there not being some information I wanted, so I needed to re-run anyway. And when format/{2,3} didn’t complain about extra args, I often thought “there should be more output … where is it? … oh, yeah, the args don’t…

Very briefly: First, my original post was only because of the inconsistency between the two symmetrical cases: a) too many arguments and b) not enough arguments. One was an error and the other one was swallowed silently. You got now several suggestions as to how to make format/2,3 behave leniently…

user_error correspond to STDERR, right? Then definitely there. That’s why it exists. Observe the perl program mentioned above: What’s on STDERR: $ perl -e 'printf "%d %s %s %s %s\n", "x", "a", "b", "c"; printf "Ok, Buddy!\n";' >/dev/null Argument "x" isn't numeric in printf at test.pl line 3. Mi…

I agree, I agree. But: it all depends on “how big is the mistake” and should it really block me or the CI pipeline etc. In effect, there should be a setting going from “picky/crash” to “whatever/I’ll print something”, to be set on the in-program context (maybe scoped to the procedure, or the module,…

(SWI-)Prolog’s I/O indeed has some old flavor to it. It isn’t too bad though: For quick and dirty output for debugging purposes, use debug/3. That is by default silent, so your application won’t crash. If you enable a message channel you probably want to see the output. Still, debug/3 ultima…

None of this provides good support for logging. See SWI-Prolog package: log4p Note: Prolog packages may not have good documentation and or support, so caveat emptor

Can I make Prolog's "format/x" family behave leniently?

Split Topic

EricGT January 26, 2020, 4:05pm 11

See recent changes regarding format/2 format/3 in this post.

Topic		Replies	Views
Too many arguments to format/2 General	12	3144	January 25, 2020
Sharing prolog-fmt: authorative Prolog formatter General software	13	161	June 22, 2026
Unintuitive debug/3 - format/2 interaction Help! printing , terminal	7	120	July 1, 2026
Inconsistent number of digits in exponents when printing float numbers Help!	0	504	February 22, 2022
Making format/2;3 deterministic when formatting numbers Help!	5	573	April 1, 2021

Can I make Prolog's "format/x" family behave leniently?

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