Re: [ats-lang-users] strange compiler error message

[Guillaume B. <gui...@gm...>]

Hi,

The type int -> int means any function taking integers to integers, possibly
non terminating, with side effects and/or raising an exception.
The type int -<> int means that all side effects are disallowed : the
function must terminate, without raising any exception, writing something on
somewhere nor modifying some reference or array.
The type int -<fun> int is the same as int -<> int, because 'fun' means that
this is a normal function (this is the default), and because tagged arrow
disallow every side effect by default.

Now you could think that your code should compile because the function id
terminate and has obviously no side effect. But when you write fun
id(x:int):int = x:int, you tell the compiler that the function id is a
normal function and can have side effects. The compiler agrees with that,
and what he remembers is that id is of type int -> int (or int -<fun1> int,
which is the same, the 1 meaning that any side effect is allowed), and
doesn’t accept it as a value for bar, because it is expected only pure and
terminating functions, and that the compiler has "forgotten" that id is pure
and terminating.

To make your code compile, you should tell the compiler that id is of type
int -<> int (is pure and terminating) by writing :
fn id (x : int) :<> int = x
(note the change of fun to fn, which means that the function is not
recursive. Without this change, the compiler would complain that the
function isn’t proved to be terminating)


And I agree with you, the error message is strange, the types do mismatch.



If I am not mistaken,

Guillaume Brunerie


2010/2/2 Matthias Berndt <mat...@gm...>

> Hi,
>
> I've been trying to compile the following code:
>
> fun id(x:int):int = x:int
> val bar:(int) -<fun> int = id
>
> However i get this strange error message:
>
> /home/matthias/ATS/atshome/bin/atsopt --output test_dats.c --dynamic
> test.dats
> /home/matthias/ATS/test.dats: 31(line=2, offs=5) -- 51(line=2, offs=25):
> error(3): mismatch of static terms (tyleq):
> The needed term is: S2Efun(fun; 0; 0; S2Ecst(int); S2Ecst(int))
> The actual term is: S2Efun(fun; 0; 0; S2Ecst(int); S2Ecst(int))
> exit(ATS): uncaught exception:
> ATS_2d0_2e1_2e7_2src_2ats_error_2esats__FatalErrorException(1002)
> exit(ATS): [ccomp_file_to_file(test.dats, test_dats.c)] failed.
>
> The types obviously match, so why does it complain? I'm using anairiats
> 0.1.7
>
> Also, i'd like to know what the difference between ->, -<> and -<fun> is.
> If I
> change -<fun> to -> in the above code, anairiats doesn't complain. It gives
> the
> same message if i use -<>.
>
>
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