ghci has some crazy defaulting rules for expressions at the top level.
In particular, it tries to unify those expressions with a few
different types, including IO.
On the other hand, the let-expression is typed like regular Haskell
and you run into the monomorphism restriction.
-- ryan
On Tue, Sep 2, 2008 at 1:25 PM, Henry Laxen
Dear Group,
When I fire up ghci and define:
increment x = return (x+1)
I can say: Main> increment 1
and ghci dutifully replies 2. Also as expected, the type signature of increment is: (Num a, Monad m) => a -> m a
However, if I say:
Main> let a = increment 1
I get:
<interactive>:1:8: Ambiguous type variable `m' in the constraint: `Monad m' arising from a use of `increment' at <interactive>:1:8-18 Probable fix: add a type signature that fixes these type variable(s)
Have I, like Monsier Jourdain, been running in the IO monad all my life, and didn't even know it?
Thanks, Henry Laxen
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe