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The C# code from C# ‘pragma foreign_proc’ declarations will be placed in the bodies of static member functions of an automatically generated C# class. Since such C# code will become part of a static member function, it must not refer to the this keyword. It may however refer to static member variables or static member functions declared with ‘pragma foreign_code’.

The input and output variables for a C# ‘pragma foreign_proc’ will have C# types corresponding to their Mercury types. The exact rules for mapping Mercury types to C# types are described in C# data passing conventions.

C# code in a pragma foreign_proc declaration for any procedure whose determinism indicates that it can fail must assign a value of type bool to the variable SUCCESS_INDICATOR. For example:

:- pred string.contains_char(string, character).
:- mode string.contains_char(in, in) is semidet.

:- pragma foreign_proc("C#",
    string.contains_char(Str::in, Ch::in),
    [will_not_call_mercury, promise_pure],
    SUCCESS_INDICATOR = (Str.IndexOf(Ch) != -1);

C# code for procedures whose determinism indicates that they cannot fail should not access SUCCESS_INDICATOR.

Arguments whose mode is input will have their values set by the Mercury implementation on entry to the C# code. If the procedure succeeds, the C# code must set the values of all output arguments. If the procedure fails, the C# code need only set SUCCESS_INDICATOR to false.