test.m

:- module test.                                                                                                                                                                                                    
:- interface.                                                                                                                                                                                                      
:- import_module io.                                                                                                                                                                                               
:- pred main(io::di, io::uo) is det.                                                                                                                                                                               
:- implementation.                                                                                                                                                                                                 
                                                                                                                                                                                                                   
main(!IO) :-                                                                                                                                                                                                       
    io.write_string("Hello, world!\n", !IO).                                                                                                                                                                       
                                                                                                                                                                                                                   
:- import_module list.                                                                                                                                                                                             
:- func length(list(T)) = int.                                                                                                                                                                                     
length([])        = 0.                                                                                                                                                                                             
length([_ | Xs])  = 1 + length(Xs).
  
%$ mmc --make test
%Making Mercury/int3s/test.int3
%Making Mercury/ints/test.int
%Making Mercury/cs/test.c
%test.m:012: In clause for function `length'/1:
%test.m:012:   in function result term of clause head:
%test.m:012:   error: undefined symbol `+/2'.
%** Error making `Mercury/cs/test.c'.