= vs ->

[Frank Atanassow]

Mark Carroll wrote (on 09-10-01 20:36 -0400):
> On Tue, 9 Oct 2001, Ashley Yakeley wrote:
> 
> > At 2001-10-09 11:55, Mark Carroll wrote:
> > 
> > >What is the rationale for when Haskell demands a "=" and when it demands 
> > >a "->"?

For me, the difference is that "=" is used when the RHS (right-hand side) is
bound to a pattern (or function decl. pattern) LHS in some scope, and "->"
when the variables of the pattern on the LHS are free in the expression on the
RHS. "<-" behaves like "=".

As for "Int -> Int" vs. "\x -> x+1", though the idea of using "->" for binding
probably came from the fact that lambda abstraction introduces "->", that's
best considered an accident, i.e., you may well assume there is no relationship
between these two uses of "->". (In some type systems, they generalize to the
same thing, but not in Haskell.) In ML, they use "->" for function types but
"=>" for binding constructs.

-- 
Frank Atanassow, Information & Computing Sciences, Utrecht University
Padualaan 14, PO Box 80.089, 3508 TB Utrecht, Netherlands
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