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 <[EMAIL PROTECTED]> wrote: > 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 > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
