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root |
1.1 |
package Switch; |
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use strict; |
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use vars qw($VERSION); |
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use Carp; |
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$VERSION = '2.10'; |
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# LOAD FILTERING MODULE... |
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use Filter::Util::Call; |
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sub __(); |
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# CATCH ATTEMPTS TO CALL case OUTSIDE THE SCOPE OF ANY switch |
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$::_S_W_I_T_C_H = sub { croak "case/when statement not in switch/given block" }; |
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my $offset; |
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my $fallthrough; |
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my ($Perl5, $Perl6) = (0,0); |
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sub import |
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{ |
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$fallthrough = grep /\bfallthrough\b/, @_; |
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$offset = (caller)[2]+1; |
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filter_add({}) unless @_>1 && $_[1] eq 'noimport'; |
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my $pkg = caller; |
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no strict 'refs'; |
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for ( qw( on_defined on_exists ) ) |
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{ |
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*{"${pkg}::$_"} = \&$_; |
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} |
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*{"${pkg}::__"} = \&__ if grep /__/, @_; |
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$Perl6 = 1 if grep(/Perl\s*6/i, @_); |
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$Perl5 = 1 if grep(/Perl\s*5/i, @_) || !grep(/Perl\s*6/i, @_); |
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1; |
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} |
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sub unimport |
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{ |
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filter_del() |
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} |
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sub filter |
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{ |
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my($self) = @_ ; |
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local $Switch::file = (caller)[1]; |
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my $status = 1; |
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$status = filter_read(1_000_000); |
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return $status if $status<0; |
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$_ = filter_blocks($_,$offset); |
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$_ = "# line $offset\n" . $_ if $offset; undef $offset; |
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return $status; |
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} |
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use Text::Balanced ':ALL'; |
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sub line |
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{ |
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my ($pretext,$offset) = @_; |
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($pretext=~tr/\n/\n/)+($offset||0); |
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} |
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sub is_block |
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{ |
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local $SIG{__WARN__}=sub{die$@}; |
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local $^W=1; |
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my $ishash = defined eval 'my $hr='.$_[0]; |
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undef $@; |
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return !$ishash; |
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} |
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my $EOP = qr/\n\n|\Z/; |
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my $CUT = qr/\n=cut.*$EOP/; |
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my $pod_or_DATA = qr/ ^=(?:head[1-4]|item) .*? $CUT |
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| ^=pod .*? $CUT |
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| ^=for .*? $EOP |
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| ^=begin \s* (\S+) .*? \n=end \s* \1 .*? $EOP |
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| ^__(DATA|END)__\n.* |
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/smx; |
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my $casecounter = 1; |
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sub filter_blocks |
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{ |
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my ($source, $line) = @_; |
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return $source unless $Perl5 && $source =~ /case|switch/ |
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|| $Perl6 && $source =~ /when|given|default/; |
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pos $source = 0; |
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my $text = ""; |
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component: while (pos $source < length $source) |
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{ |
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if ($source =~ m/(\G\s*use\s+Switch\b)/gc) |
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{ |
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$text .= q{use Switch 'noimport'}; |
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next component; |
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} |
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my @pos = Text::Balanced::_match_quotelike(\$source,qr/\s*/,1,0); |
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if (defined $pos[0]) |
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{ |
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my $pre = substr($source,$pos[0],$pos[1]); # matched prefix |
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$text .= $pre . substr($source,$pos[2],$pos[18]-$pos[2]); |
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next component; |
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} |
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if ($source =~ m/\G\s*($pod_or_DATA)/gc) { |
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next component; |
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} |
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@pos = Text::Balanced::_match_variable(\$source,qr/\s*/); |
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if (defined $pos[0]) |
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{ |
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$text .= " " if $pos[0] < $pos[2]; |
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$text .= substr($source,$pos[0],$pos[4]-$pos[0]); |
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next component; |
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} |
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if ($Perl5 && $source =~ m/\G(\n*)(\s*)(switch)\b(?=\s*[(])/gc |
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|| $Perl6 && $source =~ m/\G(\n*)(\s*)(given)\b(?=\s*[(])/gc |
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|| $Perl6 && $source =~ m/\G(\n*)(\s*)(given)\b(.*)(?=\{)/gc) |
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{ |
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my $keyword = $3; |
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my $arg = $4; |
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$text .= $1.$2.'S_W_I_T_C_H: while (1) '; |
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unless ($arg) { |
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@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\(/,qr/\)/,qr/[[{(<]/,qr/[]})>]/,undef) |
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or do { |
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die "Bad $keyword statement (problem in the parentheses?) near $Switch::file line ", line(substr($source,0,pos $source),$line), "\n"; |
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}; |
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$arg = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
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} |
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$arg =~ s {^\s*[(]\s*%} { ( \\\%} || |
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$arg =~ s {^\s*[(]\s*m\b} { ( qr} || |
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$arg =~ s {^\s*[(]\s*/} { ( qr/} || |
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$arg =~ s {^\s*[(]\s*qw} { ( \\qw}; |
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@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef) |
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or do { |
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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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}; |
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my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
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$code =~ s/{/{ local \$::_S_W_I_T_C_H; Switch::switch $arg;/; |
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$text .= $code . 'continue {last}'; |
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next component; |
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} |
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elsif ($Perl5 && $source =~ m/\G(\s*)(case\b)(?!\s*=>)/gc |
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|| $Perl6 && $source =~ m/\G(\s*)(when\b)(?!\s*=>)/gc |
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|| $Perl6 && $source =~ m/\G(\s*)(default\b)(?=\s*\{)/gc) |
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{ |
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my $keyword = $2; |
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$text .= $1 . ($keyword eq "default" |
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? "if (1)" |
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: "if (Switch::case"); |
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if ($keyword eq "default") { |
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# Nothing to do |
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} |
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elsif (@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef)) { |
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my $code = substr($source,$pos[0],$pos[4]-$pos[0]); |
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$text .= " " if $pos[0] < $pos[2]; |
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$text .= "sub " if is_block $code; |
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$text .= filter_blocks($code,line(substr($source,0,$pos[0]),$line)) . ")"; |
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} |
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elsif (@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/[[(]/,qr/[])]/,qr/[[({]/,qr/[])}]/,undef)) { |
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my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
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$code =~ s {^\s*[(]\s*%} { ( \\\%} || |
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$code =~ s {^\s*[(]\s*m\b} { ( qr} || |
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$code =~ s {^\s*[(]\s*/} { ( qr/} || |
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$code =~ s {^\s*[(]\s*qw} { ( \\qw}; |
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$text .= " " if $pos[0] < $pos[2]; |
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$text .= "$code)"; |
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} |
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elsif ($Perl6 && do{@pos = Text::Balanced::_match_variable(\$source,qr/\s*/)}) { |
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my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
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$code =~ s {^\s*%} { \%} || |
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$code =~ s {^\s*@} { \@}; |
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$text .= " " if $pos[0] < $pos[2]; |
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$text .= "$code)"; |
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} |
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elsif ( @pos = Text::Balanced::_match_quotelike(\$source,qr/\s*/,1,0)) { |
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my $code = substr($source,$pos[2],$pos[18]-$pos[2]); |
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$code = filter_blocks($code,line(substr($source,0,$pos[2]),$line)); |
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$code =~ s {^\s*m} { qr} || |
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$code =~ s {^\s*/} { qr/} || |
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$code =~ s {^\s*qw} { \\qw}; |
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$text .= " " if $pos[0] < $pos[2]; |
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$text .= "$code)"; |
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} |
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elsif ($Perl5 && $source =~ m/\G\s*(([^\$\@{])[^\$\@{]*)(?=\s*{)/gc |
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|| $Perl6 && $source =~ m/\G\s*([^;{]*)()/gc) { |
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my $code = filter_blocks($1,line(substr($source,0,pos $source),$line)); |
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$text .= ' \\' if $2 eq '%'; |
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$text .= " $code)"; |
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} |
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else { |
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die "Bad $keyword statement (invalid $keyword value?) near $Switch::file line ", line(substr($source,0,pos $source), $line), "\n"; |
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} |
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die "Missing opening brace or semi-colon after 'when' value near $Switch::file line ", line(substr($source,0,pos $source), $line), "\n" |
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unless !$Perl6 || $source =~ m/\G(\s*)(?=;|\{)/gc; |
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do{@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef)} |
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or do { |
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if ($source =~ m/\G\s*(?=([};]|\Z))/gc) { |
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$casecounter++; |
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next component; |
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} |
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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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}; |
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my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
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$code =~ s/}(?=\s*\Z)/;last S_W_I_T_C_H }/ |
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unless $fallthrough; |
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$text .= "{ while (1) $code continue { goto C_A_S_E_$casecounter } last S_W_I_T_C_H; C_A_S_E_$casecounter: }"; |
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$casecounter++; |
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next component; |
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} |
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$source =~ m/\G(\s*(-[sm]\s+|\w+|#.*\n|\W))/gc; |
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$text .= $1; |
| 219 |
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} |
| 220 |
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$text; |
| 221 |
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} |
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sub in |
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{ |
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my ($x,$y) = @_; |
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my @numy; |
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for my $nextx ( @$x ) |
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{ |
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my $numx = ref($nextx) || defined $nextx && (~$nextx&$nextx) eq 0; |
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for my $j ( 0..$#$y ) |
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{ |
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my $nexty = $y->[$j]; |
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push @numy, ref($nexty) || defined $nexty && (~$nexty&$nexty) eq 0 |
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if @numy <= $j; |
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return 1 if $numx && $numy[$j] && $nextx==$nexty |
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|| $nextx eq $nexty; |
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| 240 |
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} |
| 241 |
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} |
| 242 |
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return ""; |
| 243 |
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} |
| 244 |
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| 245 |
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sub on_exists |
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{ |
| 247 |
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my $ref = @_==1 && ref($_[0]) eq 'HASH' ? $_[0] : { @_ }; |
| 248 |
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[ keys %$ref ] |
| 249 |
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} |
| 250 |
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| 251 |
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sub on_defined |
| 252 |
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{ |
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my $ref = @_==1 && ref($_[0]) eq 'HASH' ? $_[0] : { @_ }; |
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[ grep { defined $ref->{$_} } keys %$ref ] |
| 255 |
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} |
| 256 |
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| 257 |
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sub switch(;$) |
| 258 |
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{ |
| 259 |
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my ($s_val) = @_ ? $_[0] : $_; |
| 260 |
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my $s_ref = ref $s_val; |
| 261 |
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| 262 |
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if ($s_ref eq 'CODE') |
| 263 |
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{ |
| 264 |
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$::_S_W_I_T_C_H = |
| 265 |
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sub { my $c_val = $_[0]; |
| 266 |
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return $s_val == $c_val if ref $c_val eq 'CODE'; |
| 267 |
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return $s_val->(@$c_val) if ref $c_val eq 'ARRAY'; |
| 268 |
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return $s_val->($c_val); |
| 269 |
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}; |
| 270 |
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} |
| 271 |
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elsif ($s_ref eq "" && defined $s_val && (~$s_val&$s_val) eq 0) # NUMERIC SCALAR |
| 272 |
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{ |
| 273 |
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$::_S_W_I_T_C_H = |
| 274 |
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sub { my $c_val = $_[0]; |
| 275 |
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my $c_ref = ref $c_val; |
| 276 |
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return $s_val == $c_val if $c_ref eq "" |
| 277 |
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&& defined $c_val |
| 278 |
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&& (~$c_val&$c_val) eq 0; |
| 279 |
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return $s_val eq $c_val if $c_ref eq ""; |
| 280 |
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return in([$s_val],$c_val) if $c_ref eq 'ARRAY'; |
| 281 |
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return $c_val->($s_val) if $c_ref eq 'CODE'; |
| 282 |
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return $c_val->call($s_val) if $c_ref eq 'Switch'; |
| 283 |
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return scalar $s_val=~/$c_val/ |
| 284 |
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if $c_ref eq 'Regexp'; |
| 285 |
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return scalar $c_val->{$s_val} |
| 286 |
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if $c_ref eq 'HASH'; |
| 287 |
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return; |
| 288 |
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}; |
| 289 |
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} |
| 290 |
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elsif ($s_ref eq "") # STRING SCALAR |
| 291 |
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{ |
| 292 |
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$::_S_W_I_T_C_H = |
| 293 |
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sub { my $c_val = $_[0]; |
| 294 |
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my $c_ref = ref $c_val; |
| 295 |
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return $s_val eq $c_val if $c_ref eq ""; |
| 296 |
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return in([$s_val],$c_val) if $c_ref eq 'ARRAY'; |
| 297 |
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return $c_val->($s_val) if $c_ref eq 'CODE'; |
| 298 |
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return $c_val->call($s_val) if $c_ref eq 'Switch'; |
| 299 |
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return scalar $s_val=~/$c_val/ |
| 300 |
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if $c_ref eq 'Regexp'; |
| 301 |
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return scalar $c_val->{$s_val} |
| 302 |
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if $c_ref eq 'HASH'; |
| 303 |
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return; |
| 304 |
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}; |
| 305 |
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} |
| 306 |
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elsif ($s_ref eq 'ARRAY') |
| 307 |
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{ |
| 308 |
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$::_S_W_I_T_C_H = |
| 309 |
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sub { my $c_val = $_[0]; |
| 310 |
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my $c_ref = ref $c_val; |
| 311 |
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return in($s_val,[$c_val]) if $c_ref eq ""; |
| 312 |
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return in($s_val,$c_val) if $c_ref eq 'ARRAY'; |
| 313 |
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return $c_val->(@$s_val) if $c_ref eq 'CODE'; |
| 314 |
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return $c_val->call(@$s_val) |
| 315 |
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if $c_ref eq 'Switch'; |
| 316 |
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return scalar grep {$_=~/$c_val/} @$s_val |
| 317 |
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if $c_ref eq 'Regexp'; |
| 318 |
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return scalar grep {$c_val->{$_}} @$s_val |
| 319 |
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if $c_ref eq 'HASH'; |
| 320 |
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return; |
| 321 |
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}; |
| 322 |
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} |
| 323 |
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elsif ($s_ref eq 'Regexp') |
| 324 |
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{ |
| 325 |
|
|
$::_S_W_I_T_C_H = |
| 326 |
|
|
sub { my $c_val = $_[0]; |
| 327 |
|
|
my $c_ref = ref $c_val; |
| 328 |
|
|
return $c_val=~/s_val/ if $c_ref eq ""; |
| 329 |
|
|
return scalar grep {$_=~/s_val/} @$c_val |
| 330 |
|
|
if $c_ref eq 'ARRAY'; |
| 331 |
|
|
return $c_val->($s_val) if $c_ref eq 'CODE'; |
| 332 |
|
|
return $c_val->call($s_val) if $c_ref eq 'Switch'; |
| 333 |
|
|
return $s_val eq $c_val if $c_ref eq 'Regexp'; |
| 334 |
|
|
return grep {$_=~/$s_val/ && $c_val->{$_}} keys %$c_val |
| 335 |
|
|
if $c_ref eq 'HASH'; |
| 336 |
|
|
return; |
| 337 |
|
|
}; |
| 338 |
|
|
} |
| 339 |
|
|
elsif ($s_ref eq 'HASH') |
| 340 |
|
|
{ |
| 341 |
|
|
$::_S_W_I_T_C_H = |
| 342 |
|
|
sub { my $c_val = $_[0]; |
| 343 |
|
|
my $c_ref = ref $c_val; |
| 344 |
|
|
return $s_val->{$c_val} if $c_ref eq ""; |
| 345 |
|
|
return scalar grep {$s_val->{$_}} @$c_val |
| 346 |
|
|
if $c_ref eq 'ARRAY'; |
| 347 |
|
|
return $c_val->($s_val) if $c_ref eq 'CODE'; |
| 348 |
|
|
return $c_val->call($s_val) if $c_ref eq 'Switch'; |
| 349 |
|
|
return grep {$_=~/$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 untargetted 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 $val < 7; } |
| 713 |
|
|
case /\d/ { handle_dig_any(); } |
| 714 |
|
|
} |
| 715 |
|
|
|
| 716 |
|
|
If an untargetted C<last> statement is executed in a case block, this |
| 717 |
|
|
immediately transfers control out of the enclosing C<switch> block |
| 718 |
|
|
(in other words, there is an implicit C<last> at the end of each |
| 719 |
|
|
normal C<case> block). Thus the previous example could also have been |
| 720 |
|
|
written: |
| 721 |
|
|
|
| 722 |
|
|
switch ($val) { |
| 723 |
|
|
case [0..9] { handle_num_any(); last if $val >= 7; next; } |
| 724 |
|
|
case /\d/ { handle_dig_any(); } |
| 725 |
|
|
} |
| 726 |
|
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|
| 727 |
|
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|
| 728 |
|
|
=head2 Automating fall-through |
| 729 |
|
|
|
| 730 |
|
|
In situations where case fall-through should be the norm, rather than an |
| 731 |
|
|
exception, an endless succession of terminal C<next>s is tedious and ugly. |
| 732 |
|
|
Hence, it is possible to reverse the default behaviour by specifying |
| 733 |
|
|
the string "fallthrough" when importing the module. For example, the |
| 734 |
|
|
following code is equivalent to the first example in L<"Allowing fall-through">: |
| 735 |
|
|
|
| 736 |
|
|
use Switch 'fallthrough'; |
| 737 |
|
|
|
| 738 |
|
|
switch ($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 |
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|
|
| 749 |
|
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|
| 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 (damian@conway.org). The maintainer of this module is now Rafael |
| 854 |
|
|
Garcia-Suarez (rgarciasuarez@free.fr). |
| 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. |
