[Haskell-beginners] Forcing evalation in the IO Monad

[Philip Scott]

Hi folks,

This question is so trivial it must have been answered before, but I 
have been googling all morning to no avail so please bear with me. I've 
been wading through mires of $! and seq, deepSeq, $!! etc.. and I have 
leaned a lot of useful stuff about lazy evaluation - but I haven't been 
able to solve my problem.. What I would like to do is to force an 
expression to be fully evaluated to normal form, from inside the IO 
monad, right there and then.

For example, in GHCI, calling putStrLn does just what I want:

Debug.Trace Prelude> let a = trace "Hello" 42
Debug.Trace Prelude> putStrLn $ show a
Hello
42

Except that it only takes showable things, and it puts an annoying 
message on the screen.

What I want is something like putStrLn that doesn't print anything, and 
takes any type as its input, evaluates it to normal form and then does 
nothing else. It might be called something like 'evaluate' have a type 
like this

evaluate :: a -> IO()

It _must_ exist - and it _must_ be easier to find this sort of thing 
than I am making it, or else how did all you haskell gurus attain your 
status? Am I missing something :)

All the best,

Philip