Re: [Haskell-cafe] Re: iterative algorithms: how to do it in Haskell?

I don't know exactly what types you have as base types in your implementation, but here's a small code fragment that of what I had in mind. data Value = D Double | S String | B Bool type Stack = [Value] -- Add top stack elements plus :: Stack -> Stack plus (D x : D y : vs) = D (x+y) : vs plus ( _ : _ : _) = error "Bad operands to plus" plus _ = error "Not enough operands on stack" equal :: Stack -> Stack equal (D x : D y : vs) = B (x == y) : vs equal (S x : S y : vs) = B (x == y) : vs equal (B x : B y : vs) = B (x == y) : vs equal ( _ : _ : _) = error "Bad operands to equal" equal _ = error "Not enough operands on stack" -- Lennart On Aug 21, 2006, at 04:42 , Gene A wrote:

Lennart and all,

On 8/19/06, Lennart Augustsson wrote:

...

There are much better ways than storing strings on the stack. Like using a data type with constructors for the different types that you can store.

-- Lennart

Off topic, but .... this is important info for me! Okay then, by doing that you can define a new type that "encodes" the other types.. such that you can actually end up storing the different types such as Int, Integer,Real, String, etc into a list ..... using this new type to so that even though you are in effect storing differing types to a list.. they are actually of the same type and thus legal... without doing an explicit bunch of "read"/"show" combinations.. to actually convert.. .... like Num for example... and being able to use +,* on any of the numeric types... but can you have a list of type [Num] ?? I thought that it had to be the base types of Int, Integer, Float, Double etc.. No?

thanks, gene _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe