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From: augustss@cs.chalmers.se (Lennart Augustsson)
Newsgroups: comp.lang.misc
Subject: Re: Dynamic typing -- To Have and Have Not
Message-ID: <1991Mar14.203404.1444@mathrt0.math.chalmers.se>
Date: 14 Mar 91 20:34:04 GMT
References: <628@optima.cs.arizona.edu>
Sender: news@mathrt0.math.chalmers.se (Evald Nyhetsson)
Organization: Dep of Computer Sciences, Chalmers, Gothenburg
Lines: 28

In article <628@optima.cs.arizona.edu> gudeman@cs.arizona.edu (David Gudeman) writes:
>Statically typed languages without declarations are a step in the
>right direction, but not far enough for my taste.  You are still too
>restricted in the sorts of expressions you are allowed to write (not
>to mention that for non-toy languages, compilation is slow as a
>beejeeber).
I don't know what implementations you have tried, I don't think ML style
type inference is particularely slow (except on pathological examples).

>]  tree_insert Null         x         = Node x Null Null
>]  tree_insert (Node y l r) x | x < y = Node (tree_insert l x) r
>]  tree_insert (Node y l r) x         = Node l (tree_insert r x)
>]The compiler infers the type (i.e. you don't have to write it!)
>]  tree_insert :: (Ord a) => Tree a -> a -> Tree a
>]which means that tree_insert will work on any type of data that is a
>]member of class Ord (i.e. has < defined).
>
>Can you use this function to insert different types in the same tree?
>If so, how is it different from dynamic typing?
No, one particular tree can only contain values of one type.  I know
you find this too restrictive, I was just trying to point out that compile
time type checking does not imply that you have to declare the type
of the functions you define.



	-- Lennart Augustsson
[This signature is intentionally left blank.]