[Haskell-cafe] foldl and space problems

Gracjan Polak gracjan at acchsh.com
Mon Jun 13 09:29:21 EDT 2005

Bernard Pope wrote:
> Perhaps you could post the definition of the state type? Or even better,
> a small example of code that runs badly.

I still don't know where old code had problems, but after rewriting 
everything it seems to run smoothly now :) Thanks for all ideas, btw.

I "invented" something like this:

type RestAndState = (MyState -> [MyData]) -> MyState -> [MyData]

this is the type of funtions that take current state and continuation as 
parameters. Example:

putValues v1 v2 v3 rest state =
	[v1,v2,v3] ++ rest state

there is a bit of syntactic ugliness when state chages:

putValueEx v1 rest state =
	let newstate = state { ... } in
         [v1] ++ rest nstate

good thing is that function can be composed quite easily with ($):

putV v1 v2 v3 v4 rest = -- state skipped here :)
	putValue v1 v2 v3 $
	putValueEx v4 rest

It works as I want it to. But I have strange feeling that there must be 
a better way to "compose" foldr and state... Does anybody have any idea 
how to put monad into this?


More information about the Haskell-Cafe mailing list