ddc: Bad code generated for statement containing nothing but a curried function.

[Tac-Tics]

With the following code:

foo :: () -> ()
foo () = ()

main () = do 
  foo 
  ()

The compiler panics with:

~/Desktop$ ddc Main.ds
[1 of 1] Compiling Main
cc1: warnings being treated as errors
./Main.ddc.c: In function ‘Main_main’:
./Main.ddc.c:67: error: implicit declaration of function ‘_curry0’
ddc: PANIC in Main.Invoke
        invokeSeaCompiler: compilation of C file failed.
            pathC = ./Main.ddc.c
        
        Please report this bug to the maintainers at:
            http://trac.haskell.org/ddc
            or by emailing disciple-cafe@googlegroups.com

~/Desktop$ 

[Tac-Tics]

It looks like it only occurs for top-level definitions. Making 'foo' local compiles and runs without a problem:

main () = do 
  foo :: () -> ()
  foo () = ()
  foo 
  ()

[Tac-Tics]

The problem appears to be a missing case statement in src/Sea/Thunk.hs.

As far as I can tell, the XCurry constructor is intended to be an intermediary form of the final C tree. All instances of XCurry must be removed from the tree by the end or the outputted C code will fail to compile.

The case on line 83 of src/Sea/Thunk.hs is the only case where XCurry are mentioned, and thus, the only place where they might be removed. However, they are only removed when they appear as a child of an SAssign constructor. When a top-level function appears on a line by itself, this must not be the case, and so the default case on line 118 catches it instead. The default case passes the value along untouched, including the maligning XCurry constructor.

[erikd]

Changing the code to this:

foo :: () -> ()
foo () = ()

main ()
 = do	x = foo
	()

fixes the problem. Thats a clue.

In the original problem code the first line of main() is a statement (ie no assignment) consisting of a curried function. Since there is no assignment (ie to a variable) the curried function cannot be be used. Therefore the statement can just be droppped.

[erikd]

Fixed in:

Sun May  2 21:47:24 EST 2010  Erik de Castro Lopo <erikd@mega-nerd.com>
* Fix #179 : Bad code for statement containing nothing but a curried function.