| 1 | package Switch;
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| 2 |
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| 3 | use strict;
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| 4 | use vars qw($VERSION);
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| 5 | use Carp;
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| 6 |
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| 7 | $VERSION = '2.10_01';
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| 8 |
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| 9 |
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| 10 | # LOAD FILTERING MODULE...
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| 11 | use Filter::Util::Call;
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| 12 |
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| 13 | sub __();
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| 14 |
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| 15 | # CATCH ATTEMPTS TO CALL case OUTSIDE THE SCOPE OF ANY switch
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| 16 |
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| 17 | $::_S_W_I_T_C_H = sub { croak "case/when statement not in switch/given block" };
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| 18 |
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| 19 | my $offset;
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| 20 | my $fallthrough;
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| 21 | my ($Perl5, $Perl6) = (0,0);
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| 22 |
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| 23 | sub import
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| 24 | {
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| 25 | $fallthrough = grep /\bfallthrough\b/, @_;
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| 26 | $offset = (caller)[2]+1;
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| 27 | filter_add({}) unless @_>1 && $_[1] eq 'noimport';
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| 28 | my $pkg = caller;
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| 29 | no strict 'refs';
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| 30 | for ( qw( on_defined on_exists ) )
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| 31 | {
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| 32 | *{"${pkg}::$_"} = \&$_;
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| 33 | }
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| 34 | *{"${pkg}::__"} = \&__ if grep /__/, @_;
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| 35 | $Perl6 = 1 if grep(/Perl\s*6/i, @_);
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| 36 | $Perl5 = 1 if grep(/Perl\s*5/i, @_) || !grep(/Perl\s*6/i, @_);
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| 37 | 1;
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| 38 | }
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| 39 |
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| 40 | sub unimport
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| 41 | {
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| 42 | filter_del()
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| 43 | }
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| 44 |
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| 45 | sub filter
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| 46 | {
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| 47 | my($self) = @_ ;
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| 48 | local $Switch::file = (caller)[1];
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| 49 |
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| 50 | my $status = 1;
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| 51 | $status = filter_read(1_000_000);
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| 52 | return $status if $status<0;
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| 53 | $_ = filter_blocks($_,$offset);
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| 54 | $_ = "# line $offset\n" . $_ if $offset; undef $offset;
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| 55 | return $status;
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| 56 | }
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| 57 |
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| 58 | use Text::Balanced ':ALL';
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| 59 |
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| 60 | sub line
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| 61 | {
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| 62 | my ($pretext,$offset) = @_;
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| 63 | ($pretext=~tr/\n/\n/)+($offset||0);
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| 64 | }
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| 65 |
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| 66 | sub is_block
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| 67 | {
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| 68 | local $SIG{__WARN__}=sub{die$@};
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| 69 | local $^W=1;
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| 70 | my $ishash = defined eval 'my $hr='.$_[0];
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| 71 | undef $@;
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| 72 | return !$ishash;
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| 73 | }
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| 74 |
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| 75 |
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| 76 | my $EOP = qr/\n\n|\Z/;
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| 77 | my $CUT = qr/\n=cut.*$EOP/;
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| 78 | my $pod_or_DATA = qr/ ^=(?:head[1-4]|item) .*? $CUT
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| 79 | | ^=pod .*? $CUT
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| 80 | | ^=for .*? $EOP
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| 81 | | ^=begin \s* (\S+) .*? \n=end \s* \1 .*? $EOP
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| 82 | | ^__(DATA|END)__\n.*
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| 83 | /smx;
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| 84 |
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| 85 | my $casecounter = 1;
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| 86 | sub filter_blocks
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| 87 | {
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| 88 | my ($source, $line) = @_;
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| 89 | return $source unless $Perl5 && $source =~ /case|switch/
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| 90 | || $Perl6 && $source =~ /when|given|default/;
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| 91 | pos $source = 0;
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| 92 | my $text = "";
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| 93 | component: while (pos $source < length $source)
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| 94 | {
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| 95 | if ($source =~ m/(\G\s*use\s+Switch\b)/gc)
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| 96 | {
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| 97 | $text .= q{use Switch 'noimport'};
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| 98 | next component;
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| 99 | }
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| 100 | my @pos = Text::Balanced::_match_quotelike(\$source,qr/\s*/,1,0);
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| 101 | if (defined $pos[0])
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| 102 | {
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| 103 | my $pre = substr($source,$pos[0],$pos[1]); # matched prefix
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| 104 | $text .= $pre . substr($source,$pos[2],$pos[18]-$pos[2]);
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| 105 | next component;
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| 106 | }
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| 107 | if ($source =~ m/\G\s*($pod_or_DATA)/gc) {
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| 108 | next component;
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| 109 | }
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| 110 | @pos = Text::Balanced::_match_variable(\$source,qr/\s*/);
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| 111 | if (defined $pos[0])
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| 112 | {
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| 113 | $text .= " " if $pos[0] < $pos[2];
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| 114 | $text .= substr($source,$pos[0],$pos[4]-$pos[0]);
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| 115 | next component;
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| 116 | }
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| 117 |
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| 118 | if ($Perl5 && $source =~ m/\G(\n*)(\s*)(switch)\b(?=\s*[(])/gc
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| 119 | || $Perl6 && $source =~ m/\G(\n*)(\s*)(given)\b(?=\s*[(])/gc
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| 120 | || $Perl6 && $source =~ m/\G(\n*)(\s*)(given)\b(.*)(?=\{)/gc)
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| 121 | {
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| 122 | my $keyword = $3;
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| 123 | my $arg = $4;
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| 124 | $text .= $1.$2.'S_W_I_T_C_H: while (1) ';
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| 125 | unless ($arg) {
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| 126 | @pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\(/,qr/\)/,qr/[[{(<]/,qr/[]})>]/,undef)
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| 127 | or do {
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| 128 | die "Bad $keyword statement (problem in the parentheses?) near $Switch::file line ", line(substr($source,0,pos $source),$line), "\n";
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| 129 | };
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| 130 | $arg = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line));
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| 131 | }
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| 132 | $arg =~ s {^\s*[(]\s*%} { ( \\\%} ||
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| 133 | $arg =~ s {^\s*[(]\s*m\b} { ( qr} ||
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| 134 | $arg =~ s {^\s*[(]\s*/} { ( qr/} ||
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| 135 | $arg =~ s {^\s*[(]\s*qw} { ( \\qw};
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| 136 | @pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef)
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| 137 | or do {
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| 138 | die "Bad $keyword statement (problem in the code block?) near $Switch::file line ", line(substr($source,0, pos $source), $line), "\n";
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| 139 | };
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| 140 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line));
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| 141 | $code =~ s/{/{ local \$::_S_W_I_T_C_H; Switch::switch $arg;/;
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| 142 | $text .= $code . 'continue {last}';
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| 143 | next component;
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| 144 | }
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| 145 | elsif ($Perl5 && $source =~ m/\G(\s*)(case\b)(?!\s*=>)/gc
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| 146 | || $Perl6 && $source =~ m/\G(\s*)(when\b)(?!\s*=>)/gc
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| 147 | || $Perl6 && $source =~ m/\G(\s*)(default\b)(?=\s*\{)/gc)
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| 148 | {
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| 149 | my $keyword = $2;
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| 150 | $text .= $1 . ($keyword eq "default"
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| 151 | ? "if (1)"
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| 152 | : "if (Switch::case");
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| 153 |
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| 154 | if ($keyword eq "default") {
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| 155 | # Nothing to do
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| 156 | }
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| 157 | elsif (@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef)) {
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| 158 | my $code = substr($source,$pos[0],$pos[4]-$pos[0]);
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| 159 | $text .= " " if $pos[0] < $pos[2];
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| 160 | $text .= "sub " if is_block $code;
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| 161 | $text .= filter_blocks($code,line(substr($source,0,$pos[0]),$line)) . ")";
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| 162 | }
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| 163 | elsif (@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/[[(]/,qr/[])]/,qr/[[({]/,qr/[])}]/,undef)) {
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| 164 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line));
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| 165 | $code =~ s {^\s*[(]\s*%} { ( \\\%} ||
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| 166 | $code =~ s {^\s*[(]\s*m\b} { ( qr} ||
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| 167 | $code =~ s {^\s*[(]\s*/} { ( qr/} ||
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| 168 | $code =~ s {^\s*[(]\s*qw} { ( \\qw};
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| 169 | $text .= " " if $pos[0] < $pos[2];
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| 170 | $text .= "$code)";
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| 171 | }
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| 172 | elsif ($Perl6 && do{@pos = Text::Balanced::_match_variable(\$source,qr/\s*/)}) {
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| 173 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line));
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| 174 | $code =~ s {^\s*%} { \%} ||
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| 175 | $code =~ s {^\s*@} { \@};
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| 176 | $text .= " " if $pos[0] < $pos[2];
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| 177 | $text .= "$code)";
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| 178 | }
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| 179 | elsif ( @pos = Text::Balanced::_match_quotelike(\$source,qr/\s*/,1,0)) {
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| 180 | my $code = substr($source,$pos[2],$pos[18]-$pos[2]);
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| 181 | $code = filter_blocks($code,line(substr($source,0,$pos[2]),$line));
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| 182 | $code =~ s {^\s*m} { qr} ||
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| 183 | $code =~ s {^\s*/} { qr/} ||
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| 184 | $code =~ s {^\s*qw} { \\qw};
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| 185 | $text .= " " if $pos[0] < $pos[2];
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| 186 | $text .= "$code)";
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| 187 | }
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| 188 | elsif ($Perl5 && $source =~ m/\G\s*(([^\$\@{])[^\$\@{]*)(?=\s*{)/gc
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| 189 | || $Perl6 && $source =~ m/\G\s*([^;{]*)()/gc) {
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| 190 | my $code = filter_blocks($1,line(substr($source,0,pos $source),$line));
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| 191 | $text .= ' \\' if $2 eq '%';
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| 192 | $text .= " $code)";
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| 193 | }
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| 194 | else {
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| 195 | die "Bad $keyword statement (invalid $keyword value?) near $Switch::file line ", line(substr($source,0,pos $source), $line), "\n";
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| 196 | }
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| 197 |
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| 198 | die "Missing opening brace or semi-colon after 'when' value near $Switch::file line ", line(substr($source,0,pos $source), $line), "\n"
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| 199 | unless !$Perl6 || $source =~ m/\G(\s*)(?=;|\{)/gc;
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| 200 |
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| 201 | do{@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef)}
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| 202 | or do {
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| 203 | if ($source =~ m/\G\s*(?=([};]|\Z))/gc) {
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| 204 | $casecounter++;
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| 205 | next component;
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| 206 | }
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| 207 | die "Bad $keyword statement (problem in the code block?) near $Switch::file line ", line(substr($source,0,pos $source),$line), "\n";
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| 208 | };
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| 209 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line));
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| 210 | $code =~ s/}(?=\s*\Z)/;last S_W_I_T_C_H }/
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| 211 | unless $fallthrough;
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| 212 | $text .= "{ while (1) $code continue { goto C_A_S_E_$casecounter } last S_W_I_T_C_H; C_A_S_E_$casecounter: }";
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| 213 | $casecounter++;
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| 214 | next component;
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| 215 | }
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| 216 |
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| 217 | $source =~ m/\G(\s*(-[sm]\s+|\w+|#.*\n|\W))/gc;
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| 218 | $text .= $1;
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| 219 | }
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| 220 | $text;
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| 221 | }
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| 222 |
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| 223 |
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| 224 |
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| 225 | sub in
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| 226 | {
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| 227 | my ($x,$y) = @_;
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| 228 | my @numy;
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| 229 | for my $nextx ( @$x )
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| 230 | {
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| 231 | my $numx = ref($nextx) || defined $nextx && (~$nextx&$nextx) eq 0;
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| 232 | for my $j ( 0..$#$y )
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| 233 | {
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| 234 | my $nexty = $y->[$j];
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| 235 | push @numy, ref($nexty) || defined $nexty && (~$nexty&$nexty) eq 0
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| 236 | if @numy <= $j;
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| 237 | return 1 if $numx && $numy[$j] && $nextx==$nexty
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| 238 | || $nextx eq $nexty;
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| 239 |
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| 240 | }
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| 241 | }
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| 242 | return "";
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| 243 | }
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| 244 |
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| 245 | sub on_exists
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| 246 | {
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| 247 | my $ref = @_==1 && ref($_[0]) eq 'HASH' ? $_[0] : { @_ };
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| 248 | [ keys %$ref ]
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| 249 | }
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| 250 |
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| 251 | sub on_defined
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| 252 | {
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| 253 | my $ref = @_==1 && ref($_[0]) eq 'HASH' ? $_[0] : { @_ };
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| 254 | [ grep { defined $ref->{$_} } keys %$ref ]
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| 255 | }
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| 256 |
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| 257 | sub switch(;$)
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| 258 | {
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| 259 | my ($s_val) = @_ ? $_[0] : $_;
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| 260 | my $s_ref = ref $s_val;
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| 261 |
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| 262 | if ($s_ref eq 'CODE')
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| 263 | {
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| 264 | $::_S_W_I_T_C_H =
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| 265 | sub { my $c_val = $_[0];
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| 266 | return $s_val == $c_val if ref $c_val eq 'CODE';
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| 267 | return $s_val->(@$c_val) if ref $c_val eq 'ARRAY';
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| 268 | return $s_val->($c_val);
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| 269 | };
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| 270 | }
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| 271 | elsif ($s_ref eq "" && defined $s_val && (~$s_val&$s_val) eq 0) # NUMERIC SCALAR
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| 272 | {
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| 273 | $::_S_W_I_T_C_H =
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| 274 | sub { my $c_val = $_[0];
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| 275 | my $c_ref = ref $c_val;
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| 276 | return $s_val == $c_val if $c_ref eq ""
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| 277 | && defined $c_val
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| 278 | && (~$c_val&$c_val) eq 0;
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| 279 | return $s_val eq $c_val if $c_ref eq "";
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| 280 | return in([$s_val],$c_val) if $c_ref eq 'ARRAY';
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| 281 | return $c_val->($s_val) if $c_ref eq 'CODE';
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| 282 | return $c_val->call($s_val) if $c_ref eq 'Switch';
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| 283 | return scalar $s_val=~/$c_val/
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| 284 | if $c_ref eq 'Regexp';
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| 285 | return scalar $c_val->{$s_val}
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| 286 | if $c_ref eq 'HASH';
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| 287 | return;
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| 288 | };
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| 289 | }
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| 290 | elsif ($s_ref eq "") # STRING SCALAR
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| 291 | {
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| 292 | $::_S_W_I_T_C_H =
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| 293 | sub { my $c_val = $_[0];
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| 294 | my $c_ref = ref $c_val;
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| 295 | return $s_val eq $c_val if $c_ref eq "";
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| 296 | return in([$s_val],$c_val) if $c_ref eq 'ARRAY';
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| 297 | return $c_val->($s_val) if $c_ref eq 'CODE';
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| 298 | return $c_val->call($s_val) if $c_ref eq 'Switch';
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| 299 | return scalar $s_val=~/$c_val/
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| 300 | if $c_ref eq 'Regexp';
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| 301 | return scalar $c_val->{$s_val}
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| 302 | if $c_ref eq 'HASH';
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| 303 | return;
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| 304 | };
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| 305 | }
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| 306 | elsif ($s_ref eq 'ARRAY')
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| 307 | {
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| 308 | $::_S_W_I_T_C_H =
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| 309 | sub { my $c_val = $_[0];
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| 310 | my $c_ref = ref $c_val;
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| 311 | return in($s_val,[$c_val]) if $c_ref eq "";
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| 312 | return in($s_val,$c_val) if $c_ref eq 'ARRAY';
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| 313 | return $c_val->(@$s_val) if $c_ref eq 'CODE';
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| 314 | return $c_val->call(@$s_val)
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| 315 | if $c_ref eq 'Switch';
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| 316 | return scalar grep {$_=~/$c_val/} @$s_val
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| 317 | if $c_ref eq 'Regexp';
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| 318 | return scalar grep {$c_val->{$_}} @$s_val
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| 319 | if $c_ref eq 'HASH';
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| 320 | return;
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| 321 | };
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| 322 | }
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| 323 | elsif ($s_ref eq 'Regexp')
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| 324 | {
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| 325 | $::_S_W_I_T_C_H =
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| 326 | sub { my $c_val = $_[0];
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| 327 | my $c_ref = ref $c_val;
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| 328 | return $c_val=~/s_val/ if $c_ref eq "";
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| 329 | return scalar grep {$_=~/s_val/} @$c_val
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| 330 | if $c_ref eq 'ARRAY';
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| 331 | return $c_val->($s_val) if $c_ref eq 'CODE';
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| 332 | return $c_val->call($s_val) if $c_ref eq 'Switch';
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| 333 | return $s_val eq $c_val if $c_ref eq 'Regexp';
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| 334 | return grep {$_=~/$s_val/ && $c_val->{$_}} keys %$c_val
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| 335 | if $c_ref eq 'HASH';
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| 336 | return;
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| 337 | };
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| 338 | }
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| 339 | elsif ($s_ref eq 'HASH')
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| 340 | {
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| 341 | $::_S_W_I_T_C_H =
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| 342 | sub { my $c_val = $_[0];
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| 343 | my $c_ref = ref $c_val;
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| 344 | return $s_val->{$c_val} if $c_ref eq "";
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| 345 | return scalar grep {$s_val->{$_}} @$c_val
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| 346 | if $c_ref eq 'ARRAY';
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| 347 | return $c_val->($s_val) if $c_ref eq 'CODE';
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| 348 | return $c_val->call($s_val) if $c_ref eq 'Switch';
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| 349 | return grep {$_=~/$c_val/ && $s_val->{"$_"}} keys %$s_val
|
|---|
| 350 | if $c_ref eq 'Regexp';
|
|---|
| 351 | return $s_val==$c_val if $c_ref eq 'HASH';
|
|---|
| 352 | return;
|
|---|
| 353 | };
|
|---|
| 354 | }
|
|---|
| 355 | elsif ($s_ref eq 'Switch')
|
|---|
| 356 | {
|
|---|
| 357 | $::_S_W_I_T_C_H =
|
|---|
| 358 | sub { my $c_val = $_[0];
|
|---|
| 359 | return $s_val == $c_val if ref $c_val eq 'Switch';
|
|---|
| 360 | return $s_val->call(@$c_val)
|
|---|
| 361 | if ref $c_val eq 'ARRAY';
|
|---|
| 362 | return $s_val->call($c_val);
|
|---|
| 363 | };
|
|---|
| 364 | }
|
|---|
| 365 | else
|
|---|
| 366 | {
|
|---|
| 367 | croak "Cannot switch on $s_ref";
|
|---|
| 368 | }
|
|---|
| 369 | return 1;
|
|---|
| 370 | }
|
|---|
| 371 |
|
|---|
| 372 | sub case($) { local $SIG{__WARN__} = \&carp;
|
|---|
| 373 | $::_S_W_I_T_C_H->(@_); }
|
|---|
| 374 |
|
|---|
| 375 | # IMPLEMENT __
|
|---|
| 376 |
|
|---|
| 377 | my $placeholder = bless { arity=>1, impl=>sub{$_[1+$_[0]]} };
|
|---|
| 378 |
|
|---|
| 379 | sub __() { $placeholder }
|
|---|
| 380 |
|
|---|
| 381 | sub __arg($)
|
|---|
| 382 | {
|
|---|
| 383 | my $index = $_[0]+1;
|
|---|
| 384 | bless { arity=>0, impl=>sub{$_[$index]} };
|
|---|
| 385 | }
|
|---|
| 386 |
|
|---|
| 387 | sub hosub(&@)
|
|---|
| 388 | {
|
|---|
| 389 | # WRITE THIS
|
|---|
| 390 | }
|
|---|
| 391 |
|
|---|
| 392 | sub call
|
|---|
| 393 | {
|
|---|
| 394 | my ($self,@args) = @_;
|
|---|
| 395 | return $self->{impl}->(0,@args);
|
|---|
| 396 | }
|
|---|
| 397 |
|
|---|
| 398 | sub meta_bop(&)
|
|---|
| 399 | {
|
|---|
| 400 | my ($op) = @_;
|
|---|
| 401 | sub
|
|---|
| 402 | {
|
|---|
| 403 | my ($left, $right, $reversed) = @_;
|
|---|
| 404 | ($right,$left) = @_ if $reversed;
|
|---|
| 405 |
|
|---|
| 406 | my $rop = ref $right eq 'Switch'
|
|---|
| 407 | ? $right
|
|---|
| 408 | : bless { arity=>0, impl=>sub{$right} };
|
|---|
| 409 |
|
|---|
| 410 | my $lop = ref $left eq 'Switch'
|
|---|
| 411 | ? $left
|
|---|
| 412 | : bless { arity=>0, impl=>sub{$left} };
|
|---|
| 413 |
|
|---|
| 414 | my $arity = $lop->{arity} + $rop->{arity};
|
|---|
| 415 |
|
|---|
| 416 | return bless {
|
|---|
| 417 | arity => $arity,
|
|---|
| 418 | impl => sub { my $start = shift;
|
|---|
| 419 | return $op->($lop->{impl}->($start,@_),
|
|---|
| 420 | $rop->{impl}->($start+$lop->{arity},@_));
|
|---|
| 421 | }
|
|---|
| 422 | };
|
|---|
| 423 | };
|
|---|
| 424 | }
|
|---|
| 425 |
|
|---|
| 426 | sub meta_uop(&)
|
|---|
| 427 | {
|
|---|
| 428 | my ($op) = @_;
|
|---|
| 429 | sub
|
|---|
| 430 | {
|
|---|
| 431 | my ($left) = @_;
|
|---|
| 432 |
|
|---|
| 433 | my $lop = ref $left eq 'Switch'
|
|---|
| 434 | ? $left
|
|---|
| 435 | : bless { arity=>0, impl=>sub{$left} };
|
|---|
| 436 |
|
|---|
| 437 | my $arity = $lop->{arity};
|
|---|
| 438 |
|
|---|
| 439 | return bless {
|
|---|
| 440 | arity => $arity,
|
|---|
| 441 | impl => sub { $op->($lop->{impl}->(@_)) }
|
|---|
| 442 | };
|
|---|
| 443 | };
|
|---|
| 444 | }
|
|---|
| 445 |
|
|---|
| 446 |
|
|---|
| 447 | use overload
|
|---|
| 448 | "+" => meta_bop {$_[0] + $_[1]},
|
|---|
| 449 | "-" => meta_bop {$_[0] - $_[1]},
|
|---|
| 450 | "*" => meta_bop {$_[0] * $_[1]},
|
|---|
| 451 | "/" => meta_bop {$_[0] / $_[1]},
|
|---|
| 452 | "%" => meta_bop {$_[0] % $_[1]},
|
|---|
| 453 | "**" => meta_bop {$_[0] ** $_[1]},
|
|---|
| 454 | "<<" => meta_bop {$_[0] << $_[1]},
|
|---|
| 455 | ">>" => meta_bop {$_[0] >> $_[1]},
|
|---|
| 456 | "x" => meta_bop {$_[0] x $_[1]},
|
|---|
| 457 | "." => meta_bop {$_[0] . $_[1]},
|
|---|
| 458 | "<" => meta_bop {$_[0] < $_[1]},
|
|---|
| 459 | "<=" => meta_bop {$_[0] <= $_[1]},
|
|---|
| 460 | ">" => meta_bop {$_[0] > $_[1]},
|
|---|
| 461 | ">=" => meta_bop {$_[0] >= $_[1]},
|
|---|
| 462 | "==" => meta_bop {$_[0] == $_[1]},
|
|---|
| 463 | "!=" => meta_bop {$_[0] != $_[1]},
|
|---|
| 464 | "<=>" => meta_bop {$_[0] <=> $_[1]},
|
|---|
| 465 | "lt" => meta_bop {$_[0] lt $_[1]},
|
|---|
| 466 | "le" => meta_bop {$_[0] le $_[1]},
|
|---|
| 467 | "gt" => meta_bop {$_[0] gt $_[1]},
|
|---|
| 468 | "ge" => meta_bop {$_[0] ge $_[1]},
|
|---|
| 469 | "eq" => meta_bop {$_[0] eq $_[1]},
|
|---|
| 470 | "ne" => meta_bop {$_[0] ne $_[1]},
|
|---|
| 471 | "cmp" => meta_bop {$_[0] cmp $_[1]},
|
|---|
| 472 | "\&" => meta_bop {$_[0] & $_[1]},
|
|---|
| 473 | "^" => meta_bop {$_[0] ^ $_[1]},
|
|---|
| 474 | "|" => meta_bop {$_[0] | $_[1]},
|
|---|
| 475 | "atan2" => meta_bop {atan2 $_[0], $_[1]},
|
|---|
| 476 |
|
|---|
| 477 | "neg" => meta_uop {-$_[0]},
|
|---|
| 478 | "!" => meta_uop {!$_[0]},
|
|---|
| 479 | "~" => meta_uop {~$_[0]},
|
|---|
| 480 | "cos" => meta_uop {cos $_[0]},
|
|---|
| 481 | "sin" => meta_uop {sin $_[0]},
|
|---|
| 482 | "exp" => meta_uop {exp $_[0]},
|
|---|
| 483 | "abs" => meta_uop {abs $_[0]},
|
|---|
| 484 | "log" => meta_uop {log $_[0]},
|
|---|
| 485 | "sqrt" => meta_uop {sqrt $_[0]},
|
|---|
| 486 | "bool" => sub { croak "Can't use && or || in expression containing __" },
|
|---|
| 487 |
|
|---|
| 488 | # "&()" => sub { $_[0]->{impl} },
|
|---|
| 489 |
|
|---|
| 490 | # "||" => meta_bop {$_[0] || $_[1]},
|
|---|
| 491 | # "&&" => meta_bop {$_[0] && $_[1]},
|
|---|
| 492 | # fallback => 1,
|
|---|
| 493 | ;
|
|---|
| 494 | 1;
|
|---|
| 495 |
|
|---|
| 496 | __END__
|
|---|
| 497 |
|
|---|
| 498 |
|
|---|
| 499 | =head1 NAME
|
|---|
| 500 |
|
|---|
| 501 | Switch - A switch statement for Perl
|
|---|
| 502 |
|
|---|
| 503 | =head1 VERSION
|
|---|
| 504 |
|
|---|
| 505 | This document describes version 2.10 of Switch,
|
|---|
| 506 | released Dec 29, 2003.
|
|---|
| 507 |
|
|---|
| 508 | =head1 SYNOPSIS
|
|---|
| 509 |
|
|---|
| 510 | use Switch;
|
|---|
| 511 |
|
|---|
| 512 | switch ($val) {
|
|---|
| 513 |
|
|---|
| 514 | case 1 { print "number 1" }
|
|---|
| 515 | case "a" { print "string a" }
|
|---|
| 516 | case [1..10,42] { print "number in list" }
|
|---|
| 517 | case (@array) { print "number in list" }
|
|---|
| 518 | case /\w+/ { print "pattern" }
|
|---|
| 519 | case qr/\w+/ { print "pattern" }
|
|---|
| 520 | case (%hash) { print "entry in hash" }
|
|---|
| 521 | case (\%hash) { print "entry in hash" }
|
|---|
| 522 | case (\&sub) { print "arg to subroutine" }
|
|---|
| 523 | else { print "previous case not true" }
|
|---|
| 524 | }
|
|---|
| 525 |
|
|---|
| 526 | =head1 BACKGROUND
|
|---|
| 527 |
|
|---|
| 528 | [Skip ahead to L<"DESCRIPTION"> if you don't care about the whys
|
|---|
| 529 | and wherefores of this control structure]
|
|---|
| 530 |
|
|---|
| 531 | In seeking to devise a "Swiss Army" case mechanism suitable for Perl,
|
|---|
| 532 | it is useful to generalize this notion of distributed conditional
|
|---|
| 533 | testing as far as possible. Specifically, the concept of "matching"
|
|---|
| 534 | between the switch value and the various case values need not be
|
|---|
| 535 | restricted to numeric (or string or referential) equality, as it is in other
|
|---|
| 536 | languages. Indeed, as Table 1 illustrates, Perl
|
|---|
| 537 | offers at least eighteen different ways in which two values could
|
|---|
| 538 | generate a match.
|
|---|
| 539 |
|
|---|
| 540 | Table 1: Matching a switch value ($s) with a case value ($c)
|
|---|
| 541 |
|
|---|
| 542 | Switch Case Type of Match Implied Matching Code
|
|---|
| 543 | Value Value
|
|---|
| 544 | ====== ===== ===================== =============
|
|---|
| 545 |
|
|---|
| 546 | number same numeric or referential match if $s == $c;
|
|---|
| 547 | or ref equality
|
|---|
| 548 |
|
|---|
| 549 | object method result of method call match if $s->$c();
|
|---|
| 550 | ref name match if defined $s->$c();
|
|---|
| 551 | or ref
|
|---|
| 552 |
|
|---|
| 553 | other other string equality match if $s eq $c;
|
|---|
| 554 | non-ref non-ref
|
|---|
| 555 | scalar scalar
|
|---|
| 556 |
|
|---|
| 557 | string regexp pattern match match if $s =~ /$c/;
|
|---|
| 558 |
|
|---|
| 559 | array scalar array entry existence match if 0<=$c && $c<@$s;
|
|---|
| 560 | ref array entry definition match if defined $s->[$c];
|
|---|
| 561 | array entry truth match if $s->[$c];
|
|---|
| 562 |
|
|---|
| 563 | array array array intersection match if intersects(@$s, @$c);
|
|---|
| 564 | ref ref (apply this table to
|
|---|
| 565 | all pairs of elements
|
|---|
| 566 | $s->[$i] and
|
|---|
| 567 | $c->[$j])
|
|---|
| 568 |
|
|---|
| 569 | array regexp array grep match if grep /$c/, @$s;
|
|---|
| 570 | ref
|
|---|
| 571 |
|
|---|
| 572 | hash scalar hash entry existence match if exists $s->{$c};
|
|---|
| 573 | ref hash entry definition match if defined $s->{$c};
|
|---|
| 574 | hash entry truth match if $s->{$c};
|
|---|
| 575 |
|
|---|
| 576 | hash regexp hash grep match if grep /$c/, keys %$s;
|
|---|
| 577 | ref
|
|---|
| 578 |
|
|---|
| 579 | sub scalar return value defn match if defined $s->($c);
|
|---|
| 580 | ref return value truth match if $s->($c);
|
|---|
| 581 |
|
|---|
| 582 | sub array return value defn match if defined $s->(@$c);
|
|---|
| 583 | ref ref return value truth match if $s->(@$c);
|
|---|
| 584 |
|
|---|
| 585 |
|
|---|
| 586 | In reality, Table 1 covers 31 alternatives, because only the equality and
|
|---|
| 587 | intersection tests are commutative; in all other cases, the roles of
|
|---|
| 588 | the C<$s> and C<$c> variables could be reversed to produce a
|
|---|
| 589 | different test. For example, instead of testing a single hash for
|
|---|
| 590 | the existence of a series of keys (C<match if exists $s-E<gt>{$c}>),
|
|---|
| 591 | one could test for the existence of a single key in a series of hashes
|
|---|
| 592 | (C<match if exists $c-E<gt>{$s}>).
|
|---|
| 593 |
|
|---|
| 594 | As L<perltodo> observes, a Perl case mechanism must support all these
|
|---|
| 595 | "ways to do it".
|
|---|
| 596 |
|
|---|
| 597 |
|
|---|
| 598 | =head1 DESCRIPTION
|
|---|
| 599 |
|
|---|
| 600 | The Switch.pm module implements a generalized case mechanism that covers
|
|---|
| 601 | the numerous possible combinations of switch and case values described above.
|
|---|
| 602 |
|
|---|
| 603 | The module augments the standard Perl syntax with two new control
|
|---|
| 604 | statements: C<switch> and C<case>. The C<switch> statement takes a
|
|---|
| 605 | single scalar argument of any type, specified in parentheses.
|
|---|
| 606 | C<switch> stores this value as the
|
|---|
| 607 | current switch value in a (localized) control variable.
|
|---|
| 608 | The value is followed by a block which may contain one or more
|
|---|
| 609 | Perl statements (including the C<case> statement described below).
|
|---|
| 610 | The block is unconditionally executed once the switch value has
|
|---|
| 611 | been cached.
|
|---|
| 612 |
|
|---|
| 613 | A C<case> statement takes a single scalar argument (in mandatory
|
|---|
| 614 | parentheses if it's a variable; otherwise the parens are optional) and
|
|---|
| 615 | selects the appropriate type of matching between that argument and the
|
|---|
| 616 | current switch value. The type of matching used is determined by the
|
|---|
| 617 | respective types of the switch value and the C<case> argument, as
|
|---|
| 618 | specified in Table 1. If the match is successful, the mandatory
|
|---|
| 619 | block associated with the C<case> statement is executed.
|
|---|
| 620 |
|
|---|
| 621 | In most other respects, the C<case> statement is semantically identical
|
|---|
| 622 | to an C<if> statement. For example, it can be followed by an C<else>
|
|---|
| 623 | clause, and can be used as a postfix statement qualifier.
|
|---|
| 624 |
|
|---|
| 625 | However, when a C<case> block has been executed control is automatically
|
|---|
| 626 | transferred to the statement after the immediately enclosing C<switch>
|
|---|
| 627 | block, rather than to the next statement within the block. In other
|
|---|
| 628 | words, the success of any C<case> statement prevents other cases in the
|
|---|
| 629 | same scope from executing. But see L<"Allowing fall-through"> below.
|
|---|
| 630 |
|
|---|
| 631 | Together these two new statements provide a fully generalized case
|
|---|
| 632 | mechanism:
|
|---|
| 633 |
|
|---|
| 634 | use Switch;
|
|---|
| 635 |
|
|---|
| 636 | # AND LATER...
|
|---|
| 637 |
|
|---|
| 638 | %special = ( woohoo => 1, d'oh => 1 );
|
|---|
| 639 |
|
|---|
| 640 | while (<>) {
|
|---|
| 641 | switch ($_) {
|
|---|
| 642 |
|
|---|
| 643 | case (%special) { print "homer\n"; } # if $special{$_}
|
|---|
| 644 | case /a-z/i { print "alpha\n"; } # if $_ =~ /a-z/i
|
|---|
| 645 | case [1..9] { print "small num\n"; } # if $_ in [1..9]
|
|---|
| 646 |
|
|---|
| 647 | case { $_[0] >= 10 } { # if $_ >= 10
|
|---|
| 648 | my $age = <>;
|
|---|
| 649 | switch (sub{ $_[0] < $age } ) {
|
|---|
| 650 |
|
|---|
| 651 | case 20 { print "teens\n"; } # if 20 < $age
|
|---|
| 652 | case 30 { print "twenties\n"; } # if 30 < $age
|
|---|
| 653 | else { print "history\n"; }
|
|---|
| 654 | }
|
|---|
| 655 | }
|
|---|
| 656 |
|
|---|
| 657 | print "must be punctuation\n" case /\W/; # if $_ ~= /\W/
|
|---|
| 658 | }
|
|---|
| 659 |
|
|---|
| 660 | Note that C<switch>es can be nested within C<case> (or any other) blocks,
|
|---|
| 661 | and a series of C<case> statements can try different types of matches
|
|---|
| 662 | -- hash membership, pattern match, array intersection, simple equality,
|
|---|
| 663 | etc. -- against the same switch value.
|
|---|
| 664 |
|
|---|
| 665 | The use of intersection tests against an array reference is particularly
|
|---|
| 666 | useful for aggregating integral cases:
|
|---|
| 667 |
|
|---|
| 668 | sub classify_digit
|
|---|
| 669 | {
|
|---|
| 670 | switch ($_[0]) { case 0 { return 'zero' }
|
|---|
| 671 | case [2,4,6,8] { return 'even' }
|
|---|
| 672 | case [1,3,4,7,9] { return 'odd' }
|
|---|
| 673 | case /[A-F]/i { return 'hex' }
|
|---|
| 674 | }
|
|---|
| 675 | }
|
|---|
| 676 |
|
|---|
| 677 |
|
|---|
| 678 | =head2 Allowing fall-through
|
|---|
| 679 |
|
|---|
| 680 | Fall-though (trying another case after one has already succeeded)
|
|---|
| 681 | is usually a Bad Idea in a switch statement. However, this
|
|---|
| 682 | is Perl, not a police state, so there I<is> a way to do it, if you must.
|
|---|
| 683 |
|
|---|
| 684 | If a C<case> block executes an untargeted C<next>, control is
|
|---|
| 685 | immediately transferred to the statement I<after> the C<case> statement
|
|---|
| 686 | (i.e. usually another case), rather than out of the surrounding
|
|---|
| 687 | C<switch> block.
|
|---|
| 688 |
|
|---|
| 689 | For example:
|
|---|
| 690 |
|
|---|
| 691 | switch ($val) {
|
|---|
| 692 | case 1 { handle_num_1(); next } # and try next case...
|
|---|
| 693 | case "1" { handle_str_1(); next } # and try next case...
|
|---|
| 694 | case [0..9] { handle_num_any(); } # and we're done
|
|---|
| 695 | case /\d/ { handle_dig_any(); next } # and try next case...
|
|---|
| 696 | case /.*/ { handle_str_any(); next } # and try next case...
|
|---|
| 697 | }
|
|---|
| 698 |
|
|---|
| 699 | If $val held the number C<1>, the above C<switch> block would call the
|
|---|
| 700 | first three C<handle_...> subroutines, jumping to the next case test
|
|---|
| 701 | each time it encountered a C<next>. After the thrid C<case> block
|
|---|
| 702 | was executed, control would jump to the end of the enclosing
|
|---|
| 703 | C<switch> block.
|
|---|
| 704 |
|
|---|
| 705 | On the other hand, if $val held C<10>, then only the last two C<handle_...>
|
|---|
| 706 | subroutines would be called.
|
|---|
| 707 |
|
|---|
| 708 | Note that this mechanism allows the notion of I<conditional fall-through>.
|
|---|
| 709 | For example:
|
|---|
| 710 |
|
|---|
| 711 | switch ($val) {
|
|---|
| 712 | case [0..9] { handle_num_any(); next if $val < 7; }
|
|---|
| 713 | case /\d/ { handle_dig_any(); }
|
|---|
| 714 | }
|
|---|
| 715 |
|
|---|
| 716 | If an untargeted C<last> statement is executed in a case block, this
|
|---|
| 717 | immediately transfers control out of the enclosing C<switch> block
|
|---|
| 718 | (in other words, there is an implicit C<last> at the end of each
|
|---|
| 719 | normal C<case> block). Thus the previous example could also have been
|
|---|
| 720 | written:
|
|---|
| 721 |
|
|---|
| 722 | switch ($val) {
|
|---|
| 723 | case [0..9] { handle_num_any(); last if $val >= 7; next; }
|
|---|
| 724 | case /\d/ { handle_dig_any(); }
|
|---|
| 725 | }
|
|---|
| 726 |
|
|---|
| 727 |
|
|---|
| 728 | =head2 Automating fall-through
|
|---|
| 729 |
|
|---|
| 730 | In situations where case fall-through should be the norm, rather than an
|
|---|
| 731 | exception, an endless succession of terminal C<next>s is tedious and ugly.
|
|---|
| 732 | Hence, it is possible to reverse the default behaviour by specifying
|
|---|
| 733 | the string "fallthrough" when importing the module. For example, the
|
|---|
| 734 | following code is equivalent to the first example in L<"Allowing fall-through">:
|
|---|
| 735 |
|
|---|
| 736 | use Switch 'fallthrough';
|
|---|
| 737 |
|
|---|
| 738 | switch ($val) {
|
|---|
| 739 | case 1 { handle_num_1(); }
|
|---|
| 740 | case "1" { handle_str_1(); }
|
|---|
| 741 | case [0..9] { handle_num_any(); last }
|
|---|
| 742 | case /\d/ { handle_dig_any(); }
|
|---|
| 743 | case /.*/ { handle_str_any(); }
|
|---|
| 744 | }
|
|---|
| 745 |
|
|---|
| 746 | Note the explicit use of a C<last> to preserve the non-fall-through
|
|---|
| 747 | behaviour of the third case.
|
|---|
| 748 |
|
|---|
| 749 |
|
|---|
| 750 |
|
|---|
| 751 | =head2 Alternative syntax
|
|---|
| 752 |
|
|---|
| 753 | Perl 6 will provide a built-in switch statement with essentially the
|
|---|
| 754 | same semantics as those offered by Switch.pm, but with a different
|
|---|
| 755 | pair of keywords. In Perl 6 C<switch> will be spelled C<given>, and
|
|---|
| 756 | C<case> will be pronounced C<when>. In addition, the C<when> statement
|
|---|
| 757 | will not require switch or case values to be parenthesized.
|
|---|
| 758 |
|
|---|
| 759 | This future syntax is also (largely) available via the Switch.pm module, by
|
|---|
| 760 | importing it with the argument C<"Perl6">. For example:
|
|---|
| 761 |
|
|---|
| 762 | use Switch 'Perl6';
|
|---|
| 763 |
|
|---|
| 764 | given ($val) {
|
|---|
| 765 | when 1 { handle_num_1(); }
|
|---|
| 766 | when ($str1) { handle_str_1(); }
|
|---|
| 767 | when [0..9] { handle_num_any(); last }
|
|---|
| 768 | when /\d/ { handle_dig_any(); }
|
|---|
| 769 | when /.*/ { handle_str_any(); }
|
|---|
| 770 | default { handle anything else; }
|
|---|
| 771 | }
|
|---|
| 772 |
|
|---|
| 773 | Note that scalars still need to be parenthesized, since they would be
|
|---|
| 774 | ambiguous in Perl 5.
|
|---|
| 775 |
|
|---|
| 776 | Note too that you can mix and match both syntaxes by importing the module
|
|---|
| 777 | with:
|
|---|
| 778 |
|
|---|
| 779 | use Switch 'Perl5', 'Perl6';
|
|---|
| 780 |
|
|---|
| 781 |
|
|---|
| 782 | =head2 Higher-order Operations
|
|---|
| 783 |
|
|---|
| 784 | One situation in which C<switch> and C<case> do not provide a good
|
|---|
| 785 | substitute for a cascaded C<if>, is where a switch value needs to
|
|---|
| 786 | be tested against a series of conditions. For example:
|
|---|
| 787 |
|
|---|
| 788 | sub beverage {
|
|---|
| 789 | switch (shift) {
|
|---|
| 790 |
|
|---|
| 791 | case sub { $_[0] < 10 } { return 'milk' }
|
|---|
| 792 | case sub { $_[0] < 20 } { return 'coke' }
|
|---|
| 793 | case sub { $_[0] < 30 } { return 'beer' }
|
|---|
| 794 | case sub { $_[0] < 40 } { return 'wine' }
|
|---|
| 795 | case sub { $_[0] < 50 } { return 'malt' }
|
|---|
| 796 | case sub { $_[0] < 60 } { return 'Moet' }
|
|---|
| 797 | else { return 'milk' }
|
|---|
| 798 | }
|
|---|
| 799 | }
|
|---|
| 800 |
|
|---|
| 801 | The need to specify each condition as a subroutine block is tiresome. To
|
|---|
| 802 | overcome this, when importing Switch.pm, a special "placeholder"
|
|---|
| 803 | subroutine named C<__> [sic] may also be imported. This subroutine
|
|---|
| 804 | converts (almost) any expression in which it appears to a reference to a
|
|---|
| 805 | higher-order function. That is, the expression:
|
|---|
| 806 |
|
|---|
| 807 | use Switch '__';
|
|---|
| 808 |
|
|---|
| 809 | __ < 2 + __
|
|---|
| 810 |
|
|---|
| 811 | is equivalent to:
|
|---|
| 812 |
|
|---|
| 813 | sub { $_[0] < 2 + $_[1] }
|
|---|
| 814 |
|
|---|
| 815 | With C<__>, the previous ugly case statements can be rewritten:
|
|---|
| 816 |
|
|---|
| 817 | case __ < 10 { return 'milk' }
|
|---|
| 818 | case __ < 20 { return 'coke' }
|
|---|
| 819 | case __ < 30 { return 'beer' }
|
|---|
| 820 | case __ < 40 { return 'wine' }
|
|---|
| 821 | case __ < 50 { return 'malt' }
|
|---|
| 822 | case __ < 60 { return 'Moet' }
|
|---|
| 823 | else { return 'milk' }
|
|---|
| 824 |
|
|---|
| 825 | The C<__> subroutine makes extensive use of operator overloading to
|
|---|
| 826 | perform its magic. All operations involving __ are overloaded to
|
|---|
| 827 | produce an anonymous subroutine that implements a lazy version
|
|---|
| 828 | of the original operation.
|
|---|
| 829 |
|
|---|
| 830 | The only problem is that operator overloading does not allow the
|
|---|
| 831 | boolean operators C<&&> and C<||> to be overloaded. So a case statement
|
|---|
| 832 | like this:
|
|---|
| 833 |
|
|---|
| 834 | case 0 <= __ && __ < 10 { return 'digit' }
|
|---|
| 835 |
|
|---|
| 836 | doesn't act as expected, because when it is
|
|---|
| 837 | executed, it constructs two higher order subroutines
|
|---|
| 838 | and then treats the two resulting references as arguments to C<&&>:
|
|---|
| 839 |
|
|---|
| 840 | sub { 0 <= $_[0] } && sub { $_[0] < 10 }
|
|---|
| 841 |
|
|---|
| 842 | This boolean expression is inevitably true, since both references are
|
|---|
| 843 | non-false. Fortunately, the overloaded C<'bool'> operator catches this
|
|---|
| 844 | situation and flags it as a error.
|
|---|
| 845 |
|
|---|
| 846 | =head1 DEPENDENCIES
|
|---|
| 847 |
|
|---|
| 848 | The module is implemented using Filter::Util::Call and Text::Balanced
|
|---|
| 849 | and requires both these modules to be installed.
|
|---|
| 850 |
|
|---|
| 851 | =head1 AUTHOR
|
|---|
| 852 |
|
|---|
| 853 | Damian Conway ([email protected]). The maintainer of this module is now Rafael
|
|---|
| 854 | Garcia-Suarez ([email protected]).
|
|---|
| 855 |
|
|---|
| 856 | =head1 BUGS
|
|---|
| 857 |
|
|---|
| 858 | There are undoubtedly serious bugs lurking somewhere in code this funky :-)
|
|---|
| 859 | Bug reports and other feedback are most welcome.
|
|---|
| 860 |
|
|---|
| 861 | =head1 LIMITATIONS
|
|---|
| 862 |
|
|---|
| 863 | Due to the heuristic nature of Switch.pm's source parsing, the presence
|
|---|
| 864 | of regexes specified with raw C<?...?> delimiters may cause mysterious
|
|---|
| 865 | errors. The workaround is to use C<m?...?> instead.
|
|---|
| 866 |
|
|---|
| 867 | Due to the way source filters work in Perl, you can't use Switch inside
|
|---|
| 868 | an string C<eval>.
|
|---|
| 869 |
|
|---|
| 870 | If your source file is longer then 1 million characters and you have a
|
|---|
| 871 | switch statement that crosses the 1 million (or 2 million, etc.)
|
|---|
| 872 | character boundary you will get mysterious errors. The workaround is to
|
|---|
| 873 | use smaller source files.
|
|---|
| 874 |
|
|---|
| 875 | =head1 COPYRIGHT
|
|---|
| 876 |
|
|---|
| 877 | Copyright (c) 1997-2003, Damian Conway. All Rights Reserved.
|
|---|
| 878 | This module is free software. It may be used, redistributed
|
|---|
| 879 | and/or modified under the same terms as Perl itself.
|
|---|
