Scryer-prolog: keysort/2 wrong type errors

[UWN]

prolog> ?- keysort([a-1],[X|b]).
false.                                                         % expected: type_error(list,[_|b])
prolog> ?- keysort([a],L).
error: exception thrown: error(type_error(callable, a), _12)  % expected: type_error(pair,a)

[UWN]

Further error:

prolog> ?- keysort([], L).
error: exception thrown: error(type_error(list, []), _10) % Expected: L = []

[UWN]

You really need some more systematic type testing. In general, you need

• a test for the (fully) instantiated type which produces an instantiation error or a type error. This is used for input arguments

• a test just for the type which is not associated with a instantiation error. This is typically used for output arguments.

It seem (I did not look into the code, though) that you have some more ad hoc testing implemented

[triska]

I recommend to implement such checks with a Prolog predicate like must_be/2. It is easier to reason about types on the Prolog level.

[mthom]

Is must_be/2 documented somewhere that's not the SWI site?

[triska]

SICStus Prolog provides a similar and more general version of this predicate in library(types), please see the documentation for more information:

https://sicstus.sics.se/sicstus/docs/latest4/html/sicstus.html/lib_002dtypes.html#lib_002dtypes

[UWN]

@mthom: Please note that must_be/2 is quite inconsistent. It's OK for must_be(list, Xs) but not for everything else.

[UWN]

@triska: These tests are needed on an internal level, too.