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From: ark@alice.UucP (Andrew Koenig)
Newsgroups: net.lang.apl
Subject: Re: APL structure
Message-ID: <5575@alice.uUCp>
Date: Mon, 2-Jun-86 11:33:51 EDT
Article-I.D.: alice.5575
Posted: Mon Jun  2 11:33:51 1986
Date-Received: Wed, 4-Jun-86 07:33:59 EDT
References: <1517@mmintl.UUCP>
Organization: Bell Labs, Murray Hill
Lines: 25

>Could you explain what you mean by this?  What is "direct definition"?

Direct definition is where you type

	identifier: expression

and that defines a function named "identifier."  Any variables
assigned in the expression are made local.  Arguments are referred
to by the alpha and omega symbols for left and right arguments,
respectively.  For a monadic function you can use all alpha or all
omega.  So:

	SQRT:alpha*0.5

You can also write

	identifier: e1 : e2 : e3

where e1, e2, e3 are expressions.  This means the value of the function
is e1 unless e2 is true, in which case it's e3.  Thus:

	FACT: alpha x FACT alpha-1 : alpha=0 : 1

Note that colon is not a function -- it effectively has lower precedence
than function symbols.