equality between functions

[Martin Mueller <mmueller@dfki.uni-sb.de>]

I am just wondering, why CAML light decided to allow for 

#let g x = x in g=g;;

to succeed with 

-: bool = true

but fail on (eg) 

#(function x -> x) = (function x -> x);;
Uncaught exception: Invalid_argument "equal: functional value"

I understand that there are reasons to avoid 
equality between functions, but then should not equality and
inequality be handled symmetrically?
For instance, SML/NJ does so and fails on 

- let fun g x= x in g=g end;

std_in:0.0-0.0 Error: operator and operand don't agree (equality type required)
  operator domain: ''Z * ''Z
  operand:         ('Y -> 'Y) * ('X -> 'X)
  in expression:
    = (g,g)


Could someone shed some light onto that issue? I would also 
be interested in pointers to the literature on that topic.
Is there a basic reference on equality types? 

-- Martin M"uller

---
Martin M"uller,   DFKI,  Stuhlsatzenhausweg 3,  D-66123 Saarbruecken,   Germany
Tel: +49 681 302-5329;   Fax: +49 681 302-5341;    Net: mmueller@dfki.uni-sb.de