On Tue, 2008-09-02 at 20:25 +0000, Henry Laxen 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?
Yes. This is a peculiarity of GHCi (and ghc -e) --- IO actions at top-level are executed by default, while non-IO values are simply printed out. jcc _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
