Why must 'if' clause in Perl come with either curly brackets or nothing?

This is ok:

if ($some_var==$some_value) {}

This is ok too:

print "hello" if ($some_var==$some_value);

But this raises 开发者_开发技巧an error:

if ($some_var==$some_value) print "some_message";

Why must 'if' clause in Perl come with either curly brackets or nothing?

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To avoid the well-known problem in compiler construction known as a "dangling else". See http://en.wikipedia.org/wiki/Dangling_else

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Perl has a rather complex syntax and is rather difficult to parse. I gather that curly brackets were made mandatory following an if clause so as to remove an ambiguity and make Perl code easier to parse.

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That's how the perl syntax is defined. The if (expr) BLOCK syntax requires a block, not a statement. See perlsyn ("Compound statements" section).

Excerpt:

The if statement is straightforward. Because BLOCKs are always bounded by curly brackets, there is never any ambiguity about which if an else goes with.

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if ($some_var==$some_value); is not "ok too" when I try it (nor did I expect it to be).

Why is a BLOCK required, and a plain EXPR not allowed? Because that's how Larry wanted it.

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I don't know about the curlies, but Larry spoke mentioned that the parens could have been made optional. I believe he decided against it to keep the code readable.

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I believe it simply isn't supported, this however is: print "some_message" if($some_var == $some_value);