On 06/01/11 16:07, Peter Michaux wrote:
Could some of JavaScript's statements also be allowed as expressions?
In Perl there is the common idiom when opening a file
open F, "< $f" or die "Can't open $f : $!";
In JavaScript could "throw" be an expression?
f() || throw 'f failed';
Could JavaScript's "if" become an expression? (I know JavaScript the
?: operator but this is just a for example.)
Could a Block statement also be an expression like Scheme's "begin"?
Peter
Theoretically it's possible to allow statements as expressions, but you run
into a number of practical problems:
- Precedence inversion:
a = if (b) c
So far so good. However, the substatement of an if can also be a comma
expression, which causes trouble:
a = if (b) c, d
Also, what should be stored in a if b is false? You can argue between false,
null, and undefined.
- Conflict between blocks and statements:
a = {x: while (x) { ... break x;}}
is either an object initializer or a block containing a labeled while statement.
- Semicolon insertion:
return
if (longcondition) {
...
} else {
...
}
will not do what you want. The entire if is dead code.
Waldemar
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