Re: [Haskell-cafe] Do expression definition

On Mon, 13 Sep 2010, Alexander Kotelnikov wrote:

Hello.

http://www.haskell.org/onlinereport/exps.html#sect3.14 a obscure (to me) note which says

"As indicated by the translation of do, variables bound by let have fully polymorphic types while those defined by <- are lambda bound and are thus monomorphic."

What actually does it mean?

It means that variables bound by let, may be instantiated to different types later.

And, also, would it make any difference if

do {p <- e; stmts} = let ok p = do {stmts} ok _ = fail "..." in e >>= ok

is redefined as "e >>= (\p -> do {stmts})"?

It would not make a difference because the (>>=)-expression is what the do-expression is expanded to.