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From: "Richard O'Keefe" <o...@cs.otago.ac.nz>
To: Serge Aleynikov <sal...@gmail.com>
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Date: Wed, 19 Nov 2008 10:52:24 +1300
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Cc: erlang-questi...@erlang.org
Subject: Re: [erlang-questions] conditional expressions
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On 18 Nov 2008, at 4:38 pm, Serge Aleynikov wrote:

> Your 'must' statement is not entirely accurate.

Was there any doubt about what I meant?
Let's try again:
    both 'andalso' and 'orelse' in Erlang have the
    following properties:
	the first operand must either return 'true' or 'false'
	or raise an exception;
	the second operand, if executed, must either return
	'true' or 'false' or raise an exception;
	the Dialyzer will complain if either operand looks
	as if it will return something other than 'false' or 'true';
    and above all:
	you CANNOT use them to get the same effect as
	Lisp's (OR - -) and (AND - -) or Python's similar
	operators, which allow a normal result from the
	second operand to be anything at all.

I have in fact complained about this, not because I particularly
want non-Boolean results from these operators, but because the
code that's inserted to check makes them non-tail-recursive.

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