[Haskell-cafe] State Monad

Mark Carroll mark at ixod.org
Fri Mar 4 10:42:24 EST 2005

On Fri, 4 Mar 2005, Sam G. wrote:

> Thaks a lot for your contribution, this helps me a lot, I see what I've got to do.
> However, I understand the first version (Stack.hs), but I can't get what StateM.hs is. Is
> it the same version but using state transformers, so as to be able to do IO (which I would
> need)? In fact, could you give me a simple example of how to use StackM.hs, a simple

Yes, it is. Perhaps there was a more conventional way to name it.

> example that pushes some ints and add the toppest two.

Enclosed is a programme that asks for two ints from standard input, adds
them along with a random number from 1 to 10, then prints the answer. I
hope that it helps you.

> PS: In fact I'm trying to implement a simple RPN "calculator". So at first I need +, push,
> pop and view which shows the whole list. Attached is what I started to do before I get
> your mail.

Ah, that's interesting! You've made a good start.

Thinking of stacks, I've often wondered if Haskell would be a good
language for implementing a PostScript interpreter.

All the best,

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