[Haskell-cafe] Monad strictness

[Wolfgang Jeltsch]

Am Montag, 21. November 2005 16:09 schrieb Roberto Zunino:
> Yitzchak Gale wrote:
> > In the following, why does testA work and testB diverge?
> > Where is the strictness coming from?
>
> My guess: from strict pattern matching in (>>=).

This is a problem I came across some months ago.  State uses lazy pattern 
matching (implicitely via a let expression) while StateT uses strict pattern 
matching (inside a do statement).  Both should definitely use lazy pattern 
matching, in my opinion.

> [...]

> The following StateT variant uses lazy (irrefutable) pattern match instead.

Good! :-)

> Regards,
> Roberto Zunino.

> [...]

Best wishes,
Wolfgang