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From: kurt@fluke.UUCP
Newsgroups: net.lang
Subject: Re: compound statements
Message-ID: <361@dragon.fluke.UUCP>
Date: Fri, 11-Jul-86 12:15:17 EDT
Article-I.D.: dragon.361
Posted: Fri Jul 11 12:15:17 1986
Date-Received: Tue, 15-Jul-86 06:48:18 EDT
References: <5281@topaz.RUTGERS.EDU> <2296@umcp-cs.UUCP>
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 39

Q:  Why do many languages require the statement that is the body of a
    function to be a compound statement?

A1: Languages which permit the null statement are ambiguous in a serious
    and not intuitively resolvable way.  (This was pointed out previously).

A2: Using a statement block delimits the function.  This is important
    visually and syntactically.  Just because it is *possible* to parse a
    single statement as the statement block does not make it a good idea.
    Consider the problem of parser error recovery.  Good error recovery is
    more probable when there is a good chance of finding the block/function
    delimiting END statement.  If this statement is not available, error
    recovery actions may eat into the following declaration, with confusing
    and comical results.

    As mentioned in another article, the visual delimitation is helpful in
    reading the code.  The original claim was that it was easier to read if
    the function body was a single statement.  This is possibly true, but we
    can't write parsers that say, "If the function body is only a couple of
    lines, it may be a single statement.  Otherwise it must be a block."

A3: Some recent languages use a "comb" syntactic structure to evade this
    problme altogether.  Consider this obviously psudo-code

    integer function factorial (x) is
	integer x

	if x = 1 then
	    return 1
	else
	    return x * factorial (x)
	end if
    end factorial

    The function is delimited on top and bottom.  So is the if statement.
    Ada has this approximate structure.  A 1-line body is possible, and the
    statement doesn't have to be enclosed in a block.  In fact, blocks are
    completely unnecessary in such languages, although they are often
    provided to delimit scope for local variable definition.