[m-users.] Unintelligible compiler message

[Volker Wysk]

Hi

I try to compile this little program:

:- module test1.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- implementation.
:- import_module list, char, string.
main(!IO) :-
    list.map(string.to_char_list, ["abc", "def"], Liste).

And get this error message from the compiler:

test1.m:010: In clause for `main(di, uo)':
test1.m:010:   mode error in conjunction. The next 2 error messages indicate
test1.m:010:   possible causes of this error.
test1.m:010:   In clause for `main(di, uo)':
test1.m:010:   in call to predicate `list.map'/3:
test1.m:010:   mode error: arguments
test1.m:010:   `TypeCtorInfo_15, TypeInfo_16, V_7, V_8, Liste' have the
test1.m:010:   following insts:
test1.m:010:     unique(<type_ctor_info for .string/0>),
test1.m:010:     bound(
test1.m:010:       type_info(
test1.m:010:         bound(
test1.m:010:           <type_ctor_info for list.list/1>
test1.m:010:         ),
test1.m:010:         bound(
test1.m:010:           <type_ctor_info for .character/0>
test1.m:010:         )
test1.m:010:       )
test1.m:010:     ),
test1.m:010:     free,
test1.m:010:     unique,
test1.m:010:     free
test1.m:010:   which does not match any of the modes for predicate
test1.m:010:   `list.map'/3.
test1.m:010:   In clause for `main(di, uo)':
test1.m:010:   in argument 1 of call to predicate `list.map'/3:
test1.m:010:   mode error in unification of `V_7' and higher-order term based
test1.m:010:   on multi-moded predicate `string.to_char_list'/2.
test1.m:010:   The modes of the argument variables match more than one of the
test1.m:010:   called predicate's modes.

I half-understand that message. But what I don't understand is, why does it 
mention five arguments (`TypeCtorInfo_15, TypeInfo_16, V_7, V_8, Liste') to 
the call of list.map? There are only three!

I'd like to understand that error message. Could anyone point me at how to 
find it in the documentation?

Bye,
Volker