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51 lines
1.5 KiB
Mathematica
51 lines
1.5 KiB
Mathematica
%---------------------------------------------------------------------------%
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% vim: ts=4 sw=4 et ft=mercury
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%---------------------------------------------------------------------------%
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:- module mode_selection.
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:- interface.
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:- import_module io.
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:- pred main(io::di, io::uo) is det.
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:- implementation.
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:- import_module require.
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% Currently (May 2001) we don't pass this test case,
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% because the compiler's expression flattening puts
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% the sub-goals in top-down order, rather than
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% (as the language reference manual requires)
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% ordering them bottom-up. This means that the call to
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% func2 gets flattened as
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% { V_1 = func2(In, V_2) },
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% { V_2 = In },
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% { print(V_1) }
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% rather than as
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% { V_1 = func2(In, V_2) },
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% { V_2 = In },
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% { print(V_1) }
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% which causes mode analysis to select the wrong mode in the
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% call to func2, which in turn causes a determinism error.
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%
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% The rationale for keeping the current behaviour is that
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% the naive fix of just flattening to bottom-up order
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% causes performance problems in type checking, in particular
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% when compiling compiler/options.m.
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% Eventually we ought to change the type checker to use
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% a different algorithm that doesn't have this performance
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% problem, then we can fix flattening, and this test case
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% will then pass.
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main(!IO) :-
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In = 42,
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io.print_line(func2(In, In), !IO).
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:- func func2(int, int) = string.
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:- mode func2(in, in) = out is det.
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:- mode func2(in, out) = out is det.
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:- mode func2(out, in) = out is det.
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:- mode func2(out, out) = out is det.
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func2(_, _) = _ :-
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error("called func2/2").
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