[m-users.] Useful predicates for loops of IO actions

[Volker Wysk]

Am Dienstag, dem 21.12.2021 um 16:28 +0000 schrieb Sean Charles (emacstheviking):
> Hi Volker, I use code like this all the time for !IO and folding,
> run_info(Options, !IO) :-
>     aio.format("@cy:Environment variables:@-\n", [], !IO),
> 
> 
>     list.foldl(
>         (pred(S::in, !.IO::di, !:IO::uo) is det :-
>             get_env_str(S, "", ENV, !IO),
>             aio.format("@yl:%15s:@- %s\n",
>                 [s(S), s(ENV)],
>                 !IO)
>         ), ["FELT_INST", "FELT_DOCS", "FELT_PAGER", "FELT_EDITOR",
>             "FELT_LEX",  "FELT_AST",  "FELT_TRN"],
>         !IO),
> 
> 
>     aio.format("@cy:Command line options:@-\n", [], !IO),
> 
> 
>     list.foldl(
>         (pred(K::in, !.IO::di, !:IO::uo) is det :-
>             map.lookup(Options, K, V),
>             aio.format("@yl:%15s:@- %s\n",
>                 [s(string(K)), s(string(V))],
>                 !IO)
>         ),
>         map.sorted_keys(Options),
>         !IO).
> 
> Like Zoltan says, the code practically writes itself, I’ve not found the need to for threading !IO through anything to be honest!

But that's exactly what you're doing in the example above, by using foldl.

Cheers, Volker
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