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(Revisiting) Smart match in p5

by Roy Johnson (Monsignor)
on Apr 04, 2005 at 20:03 UTC ( #444780=note: print w/replies, xml ) Need Help??


in reply to Smart match in p5

As an alternative to having hacked syntax, I've written up this little package that does the most useful (in my view) smart matches in a case-ish sort of call.
#!perl =pod =head1 NAME smatch - smart matching switch construct =head1 SYNOPSIS smatch $val => [ 1, sub { print "number 1" } ], [ 'a', sub { print 'string a' } ], [ [1,10], sub { print 'number in range' } ], # strings work, to +o [ @array, 42, sub { print 'number in list' } ], [ qr/\w+/, sub { print 'pattern' } ], [ \%hash, sub { print 'entry in hash' } ], [ \&sub, sub { print 'arg to sub' } ], [ (), sub { print 'default' } ] ;
Code and comments follow
=head1 NOTES C<smatch> aliases $_ to $val and evaluates its subsequent arguments in that context. Each subsequent argument should be an arrayref, whose last element is a coderef. The coderef will be executed if any other element yields a true value after being evaluated according to this table: Input ($in) is Example Operation =============== ============= ================================= Regex qr/foo|bar/ /$in/ Number 3.14 $_ == $in coderef sub { /foo/ } $in->($_) range specifier [100,1000] $in->[0] <= $_ and $_ <= $in->[1] (arrayref) hashref \%hash $in->{$_} any other scalar 'a string' $_ eq $in =cut use strict; use warnings; package Smatch; use Regexp::Common; sub in_range { my ($n, $lo, $hi) = @_; if ($n =~ /^RE{num}{real}$/ and $lo =~ /^$RE{num}{real}$/ and $hi =~ /^$RE{num}{real}$/) { $lo <= $hi or warnings::warnif(misc => 'Invalid range $lo .. $ +hi'); return ($lo <= $n and $n <= $hi); } else { $lo le $hi or warnings::warnif(misc => 'Invalid range $lo .. $ +hi'); return ($lo le $n and $n le $hi); } } sub smatch { local *_ = \$_[0]; CASES: for my $caselist (@_[1..$#_] ) { my $coderef = pop @$caselist; if (@$caselist) { for my $case (@$caselist) { if (my $reftype = ref $case) { $coderef->(), last CASES if ($reftype eq 'Regexp' and m{$case}) or ($reftype eq 'ARRAY' and in_range($_, @$case)) o +r ($reftype eq 'HASH' and $case->{$_}) or ($reftype eq 'CODE' and $case->($_)) or $case eq $_ ; } else { $coderef->(), last CASES if ($case =~ /^$RE{num}{real}$/ and /^$RE{num}{real +}/ and $case == $_) or $case eq $_ ; } } } else { $coderef->(); last; } } } package main; my @vals = (1, 10, 'foo1', 'bar', 'leftover'); for my $val (@vals) { no warnings 'exiting'; Smatch::smatch $val => [ 1, sub { print "$_ is 1\n" } ], [ [10, 20], sub { print "$_ hit me\n"; next } ], [ 'foo1', sub { print "$_ matched foo1\n"; next} ], [ { foo1=>1 }, sub { print "$_ found in hash\n" } ], [ qr/1/, sub { print "$_ got me, too?\n" } ], [ sub { s/bar/baz/ }, sub { print "$_ satisfied code\n" } ], [ (), sub { print "$_ fell to the default\n" } ] ; print "Done smatching $val\n"; }
Note that coderefs can alter the loop variables (bar gets changed to baz in my example. Also note that use of "next" triggers fallthrough (much like Switch.pm, on which this is based) but you'll want to turn off exiting warnings as I have done here.

Caution: Contents may have been coded under pressure.

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[james28909]: it is not an absolute date like "27" or "31". sometimes it is like wednesday or friday
[james28909]: and i need to format those special instances into an absolute date instead of "yesterday"
[stevieb]: ask a question on SoPW, and include at least a half-dozen examples of the input, and at least one example of expected output
[davido]: Exactly: SoPW. This isn't going to be solved easily in the CB.
[james28909]: in need "yesterday" and so on, to be absolute like "1" or "31"
[stevieb]: ...and throw some of your existing code into the equation as well, just so readers know you've given a try at it ;)
[james28909]: ok
[stevieb]: davido thanks for the link ;) I was being the typical lazy
[davido]: date parsing is hard. The more examples you can provide of the input (within reason) and expected output, the better.
[stevieb]: agreed. That's why I said at least a half-dozen. If enough of the different formats are present, the date/time folk may not have to request more. If they do, then at least there was a decent base to start with

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