NAME

    Syntax::Keyword::Match - a match/case syntax for perl

SYNOPSIS

       use v5.14;
       use Syntax::Keyword::Match;
    
       my $n = ...;
    
       match($n : ==) {
          case(1) { say "It's one" }
          case(2) { say "It's two" }
          case(3) { say "It's three" }
          default { say "It's something else" }
       }

DESCRIPTION

    This module provides a syntax plugin that implements a control-flow
    block called match/case, which executes at most one of a choice of
    different blocks depending on the value of its controlling expression.

    This is similar to C's switch/case syntax (copied into many other
    languages), or syntax provided by Switch::Plain.

    This is an initial, experimental implementation. Furthermore, it is
    built as a non-trivial example use-case on top of XS::Parse::Keyword,
    which is also experimental. No API or compatbility guarantees are made
    at this time.

KEYWORDS

 match

       match( EXPR : OP ) {
          ...
       }

    A match statement provides the controlling expression, comparison
    operator, and set of case statements for a match operation. The
    expression is evaluated to yield a scalar value, which is then
    compared, using the comparison operator, against each of the case
    labels. If a match is found then the body of the labelled block is
    executed. If no label matches but a default block is present, that will
    be executed instead. After a single inner block has been executed, no
    further tests are performed and execution continues from the statement
    following the match statement.

    The comparison operator must be either eq (to compare cases as strings)
    or == (to compare them as numbers).

    The braces following the match block must only contain case or default
    statements. Arbitrary code is not supported here.

    Even though a match statement is a full statement and not an
    expression, it can still yield a value if it appears as the final
    statment in its containing sub or do block. For example:

       my $result = do {
          match( $topic : == ) {
             case(1) { ... }
          }
       };

 case

       case(CONST) { STATEMENTS... }

    A case statement must only appear inside the braces of a match. It
    provides a block of code to run if the controlling expression's value
    matches the given constant in the case statement, according to the
    comparison operator.

    The CONST expression must be a compile-time constant giving a single
    scalar. Runtime expressions (such as variables or function calls) are
    not supported, nor are lists of values.

 default

    A default statement must only appear inside the braces of a match. If
    present, it must be the final choice, and there must only be one of
    them. It provides a block of code to run if the controlling
    expression's value did not match any of the given case labels.

TODO

    This is clearly an early experimental work. There are many features to
    add, and design decisions to make. Rather than attempt to list them all
    here it would be best to check the RT bug queue at

    https://rt.cpan.org/Dist/Display.html?Name=Syntax-Keyword-Match

AUTHOR

    Paul Evans <leonerd@leonerd.org.uk>