2021-09-20 19:08 AEST

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IDProjectCategoryView StatusLast Update
0000534mercuryBugpublic2021-05-28 07:32
Reporteremacstheviking 
Assigned To 
PrioritynormalSeveritycrashReproducibilityalways
StatusnewResolutionopen 
PlatformAppleOSCatalinaOS Version10.15.7
Product Version 
Target VersionFixed in Version 
Summary0000534: Uncaught Mercury exception when using try[] on predicate optimsied away to true?
DescriptionWhilst trying to use try/catch, I was calling a predicate that attempted to abstract away the perceived repetition of using trace[]. I created a local predicate, atrace, which then calls a more common code ftrace, the intent was to be able to abstract out the check for an environment variable being present and then only cause output to happen of the debug level of that variable was past a given threshold.

Zoltan says all three predicates are effectively useless, which I can almost understand, but nonetheless it caused the compiler to choke on my awful code.

Thank you.
Steps To ReproduceThis code:
on_lexer(Lx, AST) :-
    AST = astcon,
    list.filter_map(promote, lexer.tokens(Lx), ATokens),
    atrace("after promotion: %s\n\n--", [s(string(ATokens))]),
    (
        try []
            ast([], Tree, ATokens, Rest)
        then
            atrace("then block, Rest: %s\n", [s(string(Rest))])
        else
            atrace("else block\n", [])
        catch syntax_error(Pos, Why) ->
            atrace("oops: %s at %s", [s(Why), s(string(Pos))])
    ).

coupled with the following implementation of atrace and ftrace gave rise to the issue.

:- pred atrace(string::in, list(string.poly_type)::in) is det.
atrace(Format, Args) :-
    atrace(0, Format, Args).
:- pred atrace(int::in, string::in, list(string.poly_type)::in) is det.
atrace(Level, Format, Args) :-
    utils.ftrace(Level, "FELT_AST", "\n", Format, Args).

and

:- pred ftrace(
    int::in, string::in, string::in, string::in, list(string.poly_type)::in) is det.
ftrace(Level, Flag, Prefix, Format, Args) :-
    trace[io(!Dbg)] (
        utils.get_env_int(Flag, 0, N, !Dbg),
        (if N >= Level then
            io.print(Prefix, !Dbg),
            io.format(Format, Args, !Dbg)
        else true)
    ).
Additional InformationMercury Compiler, version 20.06.1, on x86_64-apple-darwin19.6.0
Copyright (C) 1993-2012 The University of Melbourne
Copyright (C) 2013-2020 The Mercury team
Usage: mmc [<options>] <arguments>
Use `mmc --help' for more information.

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Date Modified Username Field Change
2021-05-28 07:32 emacstheviking New Issue
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