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The switch Expression

This is much like the familiar switch, except the case-clauses have been replaced with match-clauses, and there's no longer a need for that irritating break to prevent fall-through. (There is also no longer the ability to fall through, but this seems like a good trade.) The specimen-expression is evaluated once, and the resulting value is matched against each pattern from top to bottom until a match is found. On the first match, the corresponding body-expression is evaluated, and its outcome is the outcome of the switch. If no patterns match, a to-be-specified*** exception is thrown.

To say the equivalent of "case constant" use "match ==constant", since the "==" pattern only matches if the specimen is the same as the expression on the right. To say the equivalent of "default", use "match _ " as the last matcher, since it will match everything not previously matched.

*** forget the expansion, or rather, postpone to appendix

Switch is precicely defined by this expansion to Kernel E:

{
    def temp := specimen-expression
    if (temp =~ pattern1) {
        body-expression1
    } else if (temp =~ pattern2) {
        body-expression2
    } ... {
        ...
    } else {
        throw(...) #Exception to be specified
}

but implementations are encouraged to optimize those uses equivalent to "case constant" and "default".