Deal with under-defined functions

[edsko]

The C specification allows to underspecify function signatures in two ways:

• The parameter list can be entirely omitted:

  void foo();

  Note that this is not the same as

  void foo(void);

  which declares a function with no argument (the former declares a function with an unspecified number of arguments).
• (Prior to C99) the number of arguments can be specified, without their types (using a separate "parameter list").

My understanding is that in both cases, function calls are subject to "default argument promotions"; see section 6.5.2.2, "Function calls" of the spec, or the section 24.3, "Argument Promotions" of the gcc manual.

The Haskell report talks about promotion in the FFI chapter.