NAME

HOI::Match - Higher-Order Imperative "Re"features in Perl

SYNOPSIS

  use HOI::Match;

  sub point_extract {
      HOI::Match::pmatch(
          "point (x _) :: r" => sub { my %args = @_; $args{x} + point_extract($args{r}) },
          "nil" => sub { 0 }
      )->(@_)
  }

  point_extract(
      [ 
          {"type" => "point", "val" => [ 1, 2 ]},
          {"type" => "point", "val" => [ 2, 4 ]},
          {"type" => "point", "val" => [ 3, 6 ]},
      ]
  ) # we will get 6

DESCRIPTION

HOI::Match offers Erlang-like pattern matching in function parameters. Currently only wildcard symbols, lists and algebraic-data-type like hashrefs are supported.

A wildcard symbol ([A-Za-z_][A-Za-z0-9_]*) matches exactly one argument. A list is represented as an array reference. An algebraic-data-typed object is represented as an hashref with two keys, namely "type", which gives its typename, and "val", which is an array reference containing zero or more wildcard symbols, lists, or algebraic-data-typed objects.

The BNF used to define the pattern grammar is given below:

Types: Type | Type COMMA Types

Type: IDENT | Type CONCAT Type | NIL | IDENT LPAREN Typelist RPAREN

Typelist: <eps> | Type Typelist

where

IDENT = [A-Za-z_][A-Za-z0-9_]*

CONCAT = ::

NIL = nil

LPAREN = (

RPAREN = )

COMMA = ,

are tokens.

pmatch

The function pmatch takes an hash-formed array, which contains pattern- subroutine pairs, where patterns are strings, sequently.

The patterns will be matched sequently. That is,

    "x, y"
    "point (_ x), y"

on arguments ( { "type" => "point", "val" => [ 1, 2 ] }, 3 ) will be successfully matched with pattern "x, y" instead of "point (_ x), y".

On a successful match, the values corresponding to identifiers in the pattern will be passed to the subroutine in a hash. You can access them as named arguments with

    my %args = @_;

Identifiers that begin with an underscore ('_') will be ignored. They will not be passed to the subroutine.

AUTHOR

withering <withering@cpan.org>

COPYRIGHT AND LICENSE

Copyright (C) 2014 by withering

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.18.2 or, at your option, any later version of Perl 5 you may have available.

cpanm HOI::Match

perl -MCPAN -e shell
install HOI::Match