Odd probable cause given by type checker

[heatsink]

In the following code, a function has been applied to zero arguments, which the type checker suggests is too many.

Prelude> foldr (>>=) [] []

<interactive>:1:6:
    Occurs check: cannot construct the infinite type: b = a -> b
    Probable cause: `>>=' is applied to too many arguments
    In the first argument of `foldr', namely `(>>=)'
    In the expression: foldr (>>=) [] []

[igloo]

Thanks for the example

[simonpj]

I'm probably the right person to look at this, but not before 6.10.

Simon

[guest]

7.4.1 gives

Prelude> foldr (>>=) [] []

<interactive>:2:13:
    Couldn't match expected type `a0 -> a0 -> b0'
                with actual type `[a1]'
    In the second argument of `foldr', namely `[]'
    In the expression: foldr (>>=) [] []
    In an equation for `it': it = foldr (>>=) [] []

I don't know whether the problem was fixed properly, but at least it does not manifest for this case.

[simonpj]

The new constraint-solving type inference algorithm does indeed do a better job here. I'll a regression test and close.

Simon