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From: sestoft@diku.dk (Peter Sestoft)
Newsgroups: comp.lang.functional
Subject: Re: Miranda FTP sites
Message-ID: <1991Jan11.100048.3121@odin.diku.dk>
Date: 11 Jan 91 10:00:48 GMT
References: <22307@rouge.usl.edu> <1991Jan10.111559.12440@odin.diku.dk> <27793.278c3bb0@kuhub.cc.ukans.edu>
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Organization: Institute of Computer Science, U of Copenhagen
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kinnersley@kuhub.cc.ukans.edu (Bill Kinnersley) writes:

>What makes a language Miranda-like?

The main difference between Miranda (TM) and Lazy ML is the syntax.
In Miranda the program lay-out has semantics: the off-side rule
determines where an expression ends, whereas (Lazy) ML has more
Pascal-like conventions, using semicolons similar punctuation.  (The
off-side rule was suggested by Peter Landin in the sixties).  This,
and the "list comprehension" notation makes (small) Miranda programs
very beautiful.  On the other hand, Miranda lacks the modules
(structures) and functors of Standard ML.  Also, Miranda is
implemented by compilation to a fixed set of combinators which are
then interpreted, and therefore execution is very slow.  But the
compiler gives much better (more comprehensible) type error messages
than the Chalmers Lazy ML compiler.

The off-side rule determines that the definition of g is a local to f in

	f x = g z
	      where z = 5
		    g y = 7

but global in

	f x = g z
	      where z = 5
	g y = 7

List comprehensions allow one to write concisely things that would
have to be expressed with combinations of map, filter, and concat,
otherwise.  Thus 
	[f x | xs <- xss; x <- xs; p x]
corresponds to
	concat (map ((map f) . (filter p)) xss)
which is less comprehensible (to me, at least).

Peter

-- 
Peter Sestoft  *  sestoft@diku.dk   *   DIKU,  Department of Computer Science
University of Copenhagen, Universitetsparken 1, DK-2100 Copenhagen O, Denmark
Tel: +45 31 39 64 66  *  Direct: +45 31 39 33 11/406  *  Fax: +45 31 39 02 21