| Commit | Line | Data |
|---|
| 3ed9f206 |
1 | package Switch; |
| 2 | |
| 3 | use strict; |
| 4 | use vars qw($VERSION); |
| 5 | use Carp; |
| 6 | |
| f43acd3e |
7 | $VERSION = '2.10'; |
| 3ed9f206 |
8 | |
| 9 | |
| 10 | # LOAD FILTERING MODULE... |
| 11 | use Filter::Util::Call; |
| 12 | |
| 13 | sub __(); |
| 14 | |
| 15 | # CATCH ATTEMPTS TO CALL case OUTSIDE THE SCOPE OF ANY switch |
| 16 | |
| 74a6a946 |
17 | $::_S_W_I_T_C_H = sub { croak "case/when statement not in switch/given block" }; |
| 3ed9f206 |
18 | |
| 19 | my $offset; |
| 20 | my $fallthrough; |
| 74a6a946 |
21 | my ($Perl5, $Perl6) = (0,0); |
| 3ed9f206 |
22 | |
| 23 | sub import |
| 24 | { |
| 25 | $fallthrough = grep /\bfallthrough\b/, @_; |
| 26 | $offset = (caller)[2]+1; |
| a1813bef |
27 | filter_add({}) unless @_>1 && $_[1] eq 'noimport'; |
| 3ed9f206 |
28 | my $pkg = caller; |
| 29 | no strict 'refs'; |
| 30 | for ( qw( on_defined on_exists ) ) |
| 31 | { |
| 32 | *{"${pkg}::$_"} = \&$_; |
| 33 | } |
| 34 | *{"${pkg}::__"} = \&__ if grep /__/, @_; |
| 74a6a946 |
35 | $Perl6 = 1 if grep(/Perl\s*6/i, @_); |
| 36 | $Perl5 = 1 if grep(/Perl\s*5/i, @_) || !grep(/Perl\s*6/i, @_); |
| 3ed9f206 |
37 | 1; |
| 38 | } |
| 39 | |
| 40 | sub unimport |
| 41 | { |
| 42 | filter_del() |
| 43 | } |
| 44 | |
| 45 | sub filter |
| 46 | { |
| 47 | my($self) = @_ ; |
| 48 | local $Switch::file = (caller)[1]; |
| 49 | |
| 50 | my $status = 1; |
| 51 | $status = filter_read(10_000); |
| 52 | return $status if $status<0; |
| 53 | $_ = filter_blocks($_,$offset); |
| 54 | $_ = "# line $offset\n" . $_ if $offset; undef $offset; |
| 3ed9f206 |
55 | return $status; |
| 56 | } |
| 57 | |
| 58 | use Text::Balanced ':ALL'; |
| 59 | |
| 60 | sub line |
| 61 | { |
| 62 | my ($pretext,$offset) = @_; |
| 74a6a946 |
63 | ($pretext=~tr/\n/\n/)+($offset||0); |
| 3ed9f206 |
64 | } |
| 65 | |
| 66 | sub is_block |
| 67 | { |
| 68 | local $SIG{__WARN__}=sub{die$@}; |
| 69 | local $^W=1; |
| 70 | my $ishash = defined eval 'my $hr='.$_[0]; |
| 71 | undef $@; |
| 72 | return !$ishash; |
| 73 | } |
| 74 | |
| d38ca171 |
75 | |
| 76 | my $EOP = qr/\n\n|\Z/; |
| 77 | my $CUT = qr/\n=cut.*$EOP/; |
| 78 | my $pod_or_DATA = qr/ ^=(?:head[1-4]|item) .*? $CUT |
| 79 | | ^=pod .*? $CUT |
| 80 | | ^=for .*? $EOP |
| 81 | | ^=begin \s* (\S+) .*? \n=end \s* \1 .*? $EOP |
| 82 | | ^__(DATA|END)__\n.* |
| 83 | /smx; |
| 84 | |
| 3ed9f206 |
85 | my $casecounter = 1; |
| 86 | sub filter_blocks |
| 87 | { |
| 88 | my ($source, $line) = @_; |
| 74a6a946 |
89 | return $source unless $Perl5 && $source =~ /case|switch/ |
| 90 | || $Perl6 && $source =~ /when|given/; |
| 3ed9f206 |
91 | pos $source = 0; |
| 92 | my $text = ""; |
| 93 | component: while (pos $source < length $source) |
| 94 | { |
| 3961318e |
95 | if ($source =~ m/(\G\s*use\s+Switch\b)/gc) |
| 3ed9f206 |
96 | { |
| 97 | $text .= q{use Switch 'noimport'}; |
| 98 | next component; |
| 99 | } |
| d38ca171 |
100 | my @pos = Text::Balanced::_match_quotelike(\$source,qr/\s*/,1,0); |
| 3ed9f206 |
101 | if (defined $pos[0]) |
| 102 | { |
| 52d8c818 |
103 | $text .= " " if $pos[0] < $pos[2]; |
| 104 | $text .= substr($source,$pos[2],$pos[18]-$pos[2]); |
| 3ed9f206 |
105 | next component; |
| 106 | } |
| d38ca171 |
107 | if ($source =~ m/\G\s*($pod_or_DATA)/gc) { |
| 108 | next component; |
| 109 | } |
| 3ed9f206 |
110 | @pos = Text::Balanced::_match_variable(\$source,qr/\s*/); |
| 111 | if (defined $pos[0]) |
| 112 | { |
| 52d8c818 |
113 | $text .= " " if $pos[0] < $pos[2]; |
| 114 | $text .= substr($source,$pos[0],$pos[4]-$pos[0]); |
| 3ed9f206 |
115 | next component; |
| 116 | } |
| 117 | |
| 74a6a946 |
118 | if ($Perl5 && $source =~ m/\G(\n*)(\s*)(switch)\b(?=\s*[(])/gc |
| 6596d39b |
119 | || $Perl6 && $source =~ m/\G(\n*)(\s*)(given)\b(?=\s*[(])/gc |
| 120 | || $Perl6 && $source =~ m/\G(\n*)(\s*)(given)\b(.*)(?=\{)/gc) |
| 3ed9f206 |
121 | { |
| 74a6a946 |
122 | my $keyword = $3; |
| 6596d39b |
123 | my $arg = $4; |
| 9c291939 |
124 | # print STDERR "[$arg]\n"; |
| 3ed9f206 |
125 | $text .= $1.$2.'S_W_I_T_C_H: while (1) '; |
| 6596d39b |
126 | unless ($arg) { |
| 127 | @pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\(/,qr/\)/,qr/[[{(<]/,qr/[]})>]/,undef) |
| 128 | or do { |
| 129 | die "Bad $keyword statement (problem in the parentheses?) near $Switch::file line ", line(substr($source,0,pos $source),$line), "\n"; |
| 130 | }; |
| 131 | $arg = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
| 132 | } |
| 3ed9f206 |
133 | $arg =~ s {^\s*[(]\s*%} { ( \\\%} || |
| 134 | $arg =~ s {^\s*[(]\s*m\b} { ( qr} || |
| 135 | $arg =~ s {^\s*[(]\s*/} { ( qr/} || |
| 136 | $arg =~ s {^\s*[(]\s*qw} { ( \\qw}; |
| 137 | @pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef) |
| 138 | or do { |
| 74a6a946 |
139 | die "Bad $keyword statement (problem in the code block?) near $Switch::file line ", line(substr($source,0, pos $source), $line), "\n"; |
| 3ed9f206 |
140 | }; |
| 141 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
| 142 | $code =~ s/{/{ local \$::_S_W_I_T_C_H; Switch::switch $arg;/; |
| 143 | $text .= $code . 'continue {last}'; |
| 144 | next component; |
| 145 | } |
| 74a6a946 |
146 | elsif ($Perl5 && $source =~ m/\G(\s*)(case\b)(?!\s*=>)/gc |
| 147 | || $Perl6 && $source =~ m/\G(\s*)(when\b)(?!\s*=>)/gc) |
| 3ed9f206 |
148 | { |
| 74a6a946 |
149 | my $keyword = $2; |
| 3ed9f206 |
150 | $text .= $1."if (Switch::case"; |
| 151 | if (@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef)) { |
| 152 | my $code = substr($source,$pos[0],$pos[4]-$pos[0]); |
| 52d8c818 |
153 | $text .= " " if $pos[0] < $pos[2]; |
| 154 | $text .= "sub " if is_block $code; |
| 155 | $text .= filter_blocks($code,line(substr($source,0,$pos[0]),$line)) . ")"; |
| 3ed9f206 |
156 | } |
| 157 | elsif (@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/[[(]/,qr/[])]/,qr/[[({]/,qr/[])}]/,undef)) { |
| 158 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
| 159 | $code =~ s {^\s*[(]\s*%} { ( \\\%} || |
| 160 | $code =~ s {^\s*[(]\s*m\b} { ( qr} || |
| 161 | $code =~ s {^\s*[(]\s*/} { ( qr/} || |
| 162 | $code =~ s {^\s*[(]\s*qw} { ( \\qw}; |
| 52d8c818 |
163 | $text .= " " if $pos[0] < $pos[2]; |
| 164 | $text .= "$code)"; |
| 3ed9f206 |
165 | } |
| 74a6a946 |
166 | elsif ($Perl6 && do{@pos = Text::Balanced::_match_variable(\$source,qr/\s*/)}) { |
| 167 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
| 168 | $code =~ s {^\s*%} { \%} || |
| 169 | $code =~ s {^\s*@} { \@}; |
| 52d8c818 |
170 | $text .= " " if $pos[0] < $pos[2]; |
| 171 | $text .= "$code)"; |
| 74a6a946 |
172 | } |
| d38ca171 |
173 | elsif ( @pos = Text::Balanced::_match_quotelike(\$source,qr/\s*/,1,0)) { |
| 3ed9f206 |
174 | my $code = substr($source,$pos[2],$pos[18]-$pos[2]); |
| 175 | $code = filter_blocks($code,line(substr($source,0,$pos[2]),$line)); |
| 176 | $code =~ s {^\s*m} { qr} || |
| 177 | $code =~ s {^\s*/} { qr/} || |
| 178 | $code =~ s {^\s*qw} { \\qw}; |
| 52d8c818 |
179 | $text .= " " if $pos[0] < $pos[2]; |
| 180 | $text .= "$code)"; |
| 3ed9f206 |
181 | } |
| 74a6a946 |
182 | elsif ($Perl5 && $source =~ m/\G\s*(([^\$\@{])[^\$\@{]*)(?=\s*{)/gc |
| 6596d39b |
183 | || $Perl6 && $source =~ m/\G\s*([^;{]*)()/gc) { |
| 3ed9f206 |
184 | my $code = filter_blocks($1,line(substr($source,0,pos $source),$line)); |
| 185 | $text .= ' \\' if $2 eq '%'; |
| 186 | $text .= " $code)"; |
| 187 | } |
| 188 | else { |
| 74a6a946 |
189 | die "Bad $keyword statement (invalid $keyword value?) near $Switch::file line ", line(substr($source,0,pos $source), $line), "\n"; |
| 3ed9f206 |
190 | } |
| 191 | |
| 6596d39b |
192 | die "Missing opening brace or semi-colon after 'when' value near $Switch::file line ", line(substr($source,0,pos $source), $line), "\n" |
| 193 | unless !$Perl6 || $source =~ m/\G(\s*)(?=;|\{)/gc; |
| 74a6a946 |
194 | |
| 195 | do{@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef)} |
| 3ed9f206 |
196 | or do { |
| 197 | if ($source =~ m/\G\s*(?=([};]|\Z))/gc) { |
| 198 | $casecounter++; |
| 199 | next component; |
| 200 | } |
| 74a6a946 |
201 | die "Bad $keyword statement (problem in the code block?) near $Switch::file line ", line(substr($source,0,pos $source),$line), "\n"; |
| 3ed9f206 |
202 | }; |
| 203 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); |
| 204 | $code =~ s/}(?=\s*\Z)/;last S_W_I_T_C_H }/ |
| 205 | unless $fallthrough; |
| 206 | $text .= "{ while (1) $code continue { goto C_A_S_E_$casecounter } last S_W_I_T_C_H; C_A_S_E_$casecounter: }"; |
| 207 | $casecounter++; |
| 208 | next component; |
| 209 | } |
| 210 | |
| d38ca171 |
211 | $source =~ m/\G(\s*(-[sm]\s+|\w+|#.*\n|\W))/gc; |
| 3ed9f206 |
212 | $text .= $1; |
| 213 | } |
| 214 | $text; |
| 215 | } |
| 216 | |
| 217 | |
| 218 | |
| 219 | sub in |
| 220 | { |
| 221 | my ($x,$y) = @_; |
| 222 | my @numy; |
| 223 | for my $nextx ( @$x ) |
| 224 | { |
| a1813bef |
225 | my $numx = ref($nextx) || defined $nextx && (~$nextx&$nextx) eq 0; |
| 3ed9f206 |
226 | for my $j ( 0..$#$y ) |
| 227 | { |
| 228 | my $nexty = $y->[$j]; |
| a1813bef |
229 | push @numy, ref($nexty) || defined $nexty && (~$nexty&$nexty) eq 0 |
| 3ed9f206 |
230 | if @numy <= $j; |
| 231 | return 1 if $numx && $numy[$j] && $nextx==$nexty |
| 232 | || $nextx eq $nexty; |
| 233 | |
| 234 | } |
| 235 | } |
| 236 | return ""; |
| 237 | } |
| 238 | |
| 239 | sub on_exists |
| 240 | { |
| 241 | my $ref = @_==1 && ref($_[0]) eq 'HASH' ? $_[0] : { @_ }; |
| 242 | [ keys %$ref ] |
| 243 | } |
| 244 | |
| 245 | sub on_defined |
| 246 | { |
| 247 | my $ref = @_==1 && ref($_[0]) eq 'HASH' ? $_[0] : { @_ }; |
| 248 | [ grep { defined $ref->{$_} } keys %$ref ] |
| 249 | } |
| 250 | |
| 251 | sub switch(;$) |
| 252 | { |
| 253 | my ($s_val) = @_ ? $_[0] : $_; |
| 254 | my $s_ref = ref $s_val; |
| 255 | |
| 256 | if ($s_ref eq 'CODE') |
| 257 | { |
| 258 | $::_S_W_I_T_C_H = |
| 259 | sub { my $c_val = $_[0]; |
| 260 | return $s_val == $c_val if ref $c_val eq 'CODE'; |
| 261 | return $s_val->(@$c_val) if ref $c_val eq 'ARRAY'; |
| 262 | return $s_val->($c_val); |
| 263 | }; |
| 264 | } |
| a1813bef |
265 | elsif ($s_ref eq "" && defined $s_val && (~$s_val&$s_val) eq 0) # NUMERIC SCALAR |
| 3ed9f206 |
266 | { |
| 267 | $::_S_W_I_T_C_H = |
| 268 | sub { my $c_val = $_[0]; |
| 269 | my $c_ref = ref $c_val; |
| 270 | return $s_val == $c_val if $c_ref eq "" |
| a1813bef |
271 | && defined $c_val |
| 3ed9f206 |
272 | && (~$c_val&$c_val) eq 0; |
| 273 | return $s_val eq $c_val if $c_ref eq ""; |
| 274 | return in([$s_val],$c_val) if $c_ref eq 'ARRAY'; |
| 275 | return $c_val->($s_val) if $c_ref eq 'CODE'; |
| 276 | return $c_val->call($s_val) if $c_ref eq 'Switch'; |
| 277 | return scalar $s_val=~/$c_val/ |
| 278 | if $c_ref eq 'Regexp'; |
| 279 | return scalar $c_val->{$s_val} |
| 280 | if $c_ref eq 'HASH'; |
| 281 | return; |
| 282 | }; |
| 283 | } |
| 284 | elsif ($s_ref eq "") # STRING SCALAR |
| 285 | { |
| 286 | $::_S_W_I_T_C_H = |
| 287 | sub { my $c_val = $_[0]; |
| 288 | my $c_ref = ref $c_val; |
| 289 | return $s_val eq $c_val if $c_ref eq ""; |
| 290 | return in([$s_val],$c_val) if $c_ref eq 'ARRAY'; |
| 291 | return $c_val->($s_val) if $c_ref eq 'CODE'; |
| 292 | return $c_val->call($s_val) if $c_ref eq 'Switch'; |
| 293 | return scalar $s_val=~/$c_val/ |
| 294 | if $c_ref eq 'Regexp'; |
| 295 | return scalar $c_val->{$s_val} |
| 296 | if $c_ref eq 'HASH'; |
| 297 | return; |
| 298 | }; |
| 299 | } |
| 300 | elsif ($s_ref eq 'ARRAY') |
| 301 | { |
| 302 | $::_S_W_I_T_C_H = |
| 303 | sub { my $c_val = $_[0]; |
| 304 | my $c_ref = ref $c_val; |
| 305 | return in($s_val,[$c_val]) if $c_ref eq ""; |
| 306 | return in($s_val,$c_val) if $c_ref eq 'ARRAY'; |
| 307 | return $c_val->(@$s_val) if $c_ref eq 'CODE'; |
| 308 | return $c_val->call(@$s_val) |
| 309 | if $c_ref eq 'Switch'; |
| 310 | return scalar grep {$_=~/$c_val/} @$s_val |
| 311 | if $c_ref eq 'Regexp'; |
| 312 | return scalar grep {$c_val->{$_}} @$s_val |
| 313 | if $c_ref eq 'HASH'; |
| 314 | return; |
| 315 | }; |
| 316 | } |
| 317 | elsif ($s_ref eq 'Regexp') |
| 318 | { |
| 319 | $::_S_W_I_T_C_H = |
| 320 | sub { my $c_val = $_[0]; |
| 321 | my $c_ref = ref $c_val; |
| 322 | return $c_val=~/s_val/ if $c_ref eq ""; |
| 323 | return scalar grep {$_=~/s_val/} @$c_val |
| 324 | if $c_ref eq 'ARRAY'; |
| 325 | return $c_val->($s_val) if $c_ref eq 'CODE'; |
| 326 | return $c_val->call($s_val) if $c_ref eq 'Switch'; |
| 327 | return $s_val eq $c_val if $c_ref eq 'Regexp'; |
| 328 | return grep {$_=~/$s_val/ && $c_val->{$_}} keys %$c_val |
| 329 | if $c_ref eq 'HASH'; |
| 330 | return; |
| 331 | }; |
| 332 | } |
| 333 | elsif ($s_ref eq 'HASH') |
| 334 | { |
| 335 | $::_S_W_I_T_C_H = |
| 336 | sub { my $c_val = $_[0]; |
| 337 | my $c_ref = ref $c_val; |
| 338 | return $s_val->{$c_val} if $c_ref eq ""; |
| 339 | return scalar grep {$s_val->{$_}} @$c_val |
| 340 | if $c_ref eq 'ARRAY'; |
| 341 | return $c_val->($s_val) if $c_ref eq 'CODE'; |
| 342 | return $c_val->call($s_val) if $c_ref eq 'Switch'; |
| 343 | return grep {$_=~/$c_val/ && $s_val->{"$_"}} keys %$s_val |
| 344 | if $c_ref eq 'Regexp'; |
| 345 | return $s_val==$c_val if $c_ref eq 'HASH'; |
| 346 | return; |
| 347 | }; |
| 348 | } |
| 349 | elsif ($s_ref eq 'Switch') |
| 350 | { |
| 351 | $::_S_W_I_T_C_H = |
| 352 | sub { my $c_val = $_[0]; |
| 353 | return $s_val == $c_val if ref $c_val eq 'Switch'; |
| 354 | return $s_val->call(@$c_val) |
| 355 | if ref $c_val eq 'ARRAY'; |
| 356 | return $s_val->call($c_val); |
| 357 | }; |
| 358 | } |
| 359 | else |
| 360 | { |
| 361 | croak "Cannot switch on $s_ref"; |
| 362 | } |
| 363 | return 1; |
| 364 | } |
| 365 | |
| d38ca171 |
366 | sub case($) { local $SIG{__WARN__} = \&carp; |
| 367 | $::_S_W_I_T_C_H->(@_); } |
| 3ed9f206 |
368 | |
| 369 | # IMPLEMENT __ |
| 370 | |
| 371 | my $placeholder = bless { arity=>1, impl=>sub{$_[1+$_[0]]} }; |
| 372 | |
| 373 | sub __() { $placeholder } |
| 374 | |
| 375 | sub __arg($) |
| 376 | { |
| 377 | my $index = $_[0]+1; |
| 378 | bless { arity=>0, impl=>sub{$_[$index]} }; |
| 379 | } |
| 380 | |
| 381 | sub hosub(&@) |
| 382 | { |
| 383 | # WRITE THIS |
| 384 | } |
| 385 | |
| 386 | sub call |
| 387 | { |
| 388 | my ($self,@args) = @_; |
| 389 | return $self->{impl}->(0,@args); |
| 390 | } |
| 391 | |
| 392 | sub meta_bop(&) |
| 393 | { |
| 394 | my ($op) = @_; |
| 395 | sub |
| 396 | { |
| 397 | my ($left, $right, $reversed) = @_; |
| 398 | ($right,$left) = @_ if $reversed; |
| 399 | |
| 400 | my $rop = ref $right eq 'Switch' |
| 401 | ? $right |
| 402 | : bless { arity=>0, impl=>sub{$right} }; |
| 403 | |
| 404 | my $lop = ref $left eq 'Switch' |
| 405 | ? $left |
| 406 | : bless { arity=>0, impl=>sub{$left} }; |
| 407 | |
| 408 | my $arity = $lop->{arity} + $rop->{arity}; |
| 409 | |
| 410 | return bless { |
| 411 | arity => $arity, |
| 412 | impl => sub { my $start = shift; |
| 413 | return $op->($lop->{impl}->($start,@_), |
| 414 | $rop->{impl}->($start+$lop->{arity},@_)); |
| 415 | } |
| 416 | }; |
| 417 | }; |
| 418 | } |
| 419 | |
| 420 | sub meta_uop(&) |
| 421 | { |
| 422 | my ($op) = @_; |
| 423 | sub |
| 424 | { |
| 425 | my ($left) = @_; |
| 426 | |
| 427 | my $lop = ref $left eq 'Switch' |
| 428 | ? $left |
| 429 | : bless { arity=>0, impl=>sub{$left} }; |
| 430 | |
| 431 | my $arity = $lop->{arity}; |
| 432 | |
| 433 | return bless { |
| 434 | arity => $arity, |
| 435 | impl => sub { $op->($lop->{impl}->(@_)) } |
| 436 | }; |
| 437 | }; |
| 438 | } |
| 439 | |
| 440 | |
| 441 | use overload |
| 442 | "+" => meta_bop {$_[0] + $_[1]}, |
| 443 | "-" => meta_bop {$_[0] - $_[1]}, |
| 444 | "*" => meta_bop {$_[0] * $_[1]}, |
| 445 | "/" => meta_bop {$_[0] / $_[1]}, |
| 446 | "%" => meta_bop {$_[0] % $_[1]}, |
| 447 | "**" => meta_bop {$_[0] ** $_[1]}, |
| 448 | "<<" => meta_bop {$_[0] << $_[1]}, |
| 449 | ">>" => meta_bop {$_[0] >> $_[1]}, |
| 450 | "x" => meta_bop {$_[0] x $_[1]}, |
| 451 | "." => meta_bop {$_[0] . $_[1]}, |
| 452 | "<" => meta_bop {$_[0] < $_[1]}, |
| 453 | "<=" => meta_bop {$_[0] <= $_[1]}, |
| 454 | ">" => meta_bop {$_[0] > $_[1]}, |
| 455 | ">=" => meta_bop {$_[0] >= $_[1]}, |
| 456 | "==" => meta_bop {$_[0] == $_[1]}, |
| 457 | "!=" => meta_bop {$_[0] != $_[1]}, |
| 458 | "<=>" => meta_bop {$_[0] <=> $_[1]}, |
| 459 | "lt" => meta_bop {$_[0] lt $_[1]}, |
| 460 | "le" => meta_bop {$_[0] le $_[1]}, |
| 461 | "gt" => meta_bop {$_[0] gt $_[1]}, |
| 462 | "ge" => meta_bop {$_[0] ge $_[1]}, |
| 463 | "eq" => meta_bop {$_[0] eq $_[1]}, |
| 464 | "ne" => meta_bop {$_[0] ne $_[1]}, |
| 465 | "cmp" => meta_bop {$_[0] cmp $_[1]}, |
| 466 | "\&" => meta_bop {$_[0] & $_[1]}, |
| 467 | "^" => meta_bop {$_[0] ^ $_[1]}, |
| 468 | "|" => meta_bop {$_[0] | $_[1]}, |
| 469 | "atan2" => meta_bop {atan2 $_[0], $_[1]}, |
| 470 | |
| 471 | "neg" => meta_uop {-$_[0]}, |
| 472 | "!" => meta_uop {!$_[0]}, |
| 473 | "~" => meta_uop {~$_[0]}, |
| 474 | "cos" => meta_uop {cos $_[0]}, |
| 475 | "sin" => meta_uop {sin $_[0]}, |
| 476 | "exp" => meta_uop {exp $_[0]}, |
| 477 | "abs" => meta_uop {abs $_[0]}, |
| 478 | "log" => meta_uop {log $_[0]}, |
| 479 | "sqrt" => meta_uop {sqrt $_[0]}, |
| 480 | "bool" => sub { croak "Can't use && or || in expression containing __" }, |
| 481 | |
| 482 | # "&()" => sub { $_[0]->{impl} }, |
| 483 | |
| 484 | # "||" => meta_bop {$_[0] || $_[1]}, |
| 485 | # "&&" => meta_bop {$_[0] && $_[1]}, |
| 486 | # fallback => 1, |
| 487 | ; |
| 488 | 1; |
| 489 | |
| 490 | __END__ |
| 491 | |
| 492 | |
| 493 | =head1 NAME |
| 494 | |
| 495 | Switch - A switch statement for Perl |
| 496 | |
| 497 | =head1 VERSION |
| 498 | |
| 218ab4da |
499 | This document describes version 2.09 of Switch, |
| 500 | released June 12, 2002. |
| 3ed9f206 |
501 | |
| 502 | =head1 SYNOPSIS |
| 503 | |
| 504 | use Switch; |
| 505 | |
| 506 | switch ($val) { |
| 507 | |
| 508 | case 1 { print "number 1" } |
| 509 | case "a" { print "string a" } |
| 510 | case [1..10,42] { print "number in list" } |
| 511 | case (@array) { print "number in list" } |
| 512 | case /\w+/ { print "pattern" } |
| 513 | case qr/\w+/ { print "pattern" } |
| 514 | case (%hash) { print "entry in hash" } |
| 515 | case (\%hash) { print "entry in hash" } |
| 516 | case (\&sub) { print "arg to subroutine" } |
| 517 | else { print "previous case not true" } |
| 518 | } |
| 519 | |
| 520 | =head1 BACKGROUND |
| 521 | |
| 522 | [Skip ahead to L<"DESCRIPTION"> if you don't care about the whys |
| 523 | and wherefores of this control structure] |
| 524 | |
| 525 | In seeking to devise a "Swiss Army" case mechanism suitable for Perl, |
| 526 | it is useful to generalize this notion of distributed conditional |
| 527 | testing as far as possible. Specifically, the concept of "matching" |
| 528 | between the switch value and the various case values need not be |
| 529 | restricted to numeric (or string or referential) equality, as it is in other |
| 530 | languages. Indeed, as Table 1 illustrates, Perl |
| 531 | offers at least eighteen different ways in which two values could |
| 532 | generate a match. |
| 533 | |
| 534 | Table 1: Matching a switch value ($s) with a case value ($c) |
| 535 | |
| 536 | Switch Case Type of Match Implied Matching Code |
| 537 | Value Value |
| 538 | ====== ===== ===================== ============= |
| 539 | |
| 540 | number same numeric or referential match if $s == $c; |
| 541 | or ref equality |
| 542 | |
| 543 | object method result of method call match if $s->$c(); |
| 544 | ref name match if defined $s->$c(); |
| 545 | or ref |
| 546 | |
| 547 | other other string equality match if $s eq $c; |
| 548 | non-ref non-ref |
| 549 | scalar scalar |
| 550 | |
| 551 | string regexp pattern match match if $s =~ /$c/; |
| 552 | |
| 553 | array scalar array entry existence match if 0<=$c && $c<@$s; |
| 554 | ref array entry definition match if defined $s->[$c]; |
| 555 | array entry truth match if $s->[$c]; |
| 556 | |
| 557 | array array array intersection match if intersects(@$s, @$c); |
| 558 | ref ref (apply this table to |
| 559 | all pairs of elements |
| 560 | $s->[$i] and |
| 561 | $c->[$j]) |
| 562 | |
| 563 | array regexp array grep match if grep /$c/, @$s; |
| 564 | ref |
| 565 | |
| 566 | hash scalar hash entry existence match if exists $s->{$c}; |
| 567 | ref hash entry definition match if defined $s->{$c}; |
| 568 | hash entry truth match if $s->{$c}; |
| 569 | |
| 570 | hash regexp hash grep match if grep /$c/, keys %$s; |
| 571 | ref |
| 572 | |
| 573 | sub scalar return value defn match if defined $s->($c); |
| 574 | ref return value truth match if $s->($c); |
| 575 | |
| 576 | sub array return value defn match if defined $s->(@$c); |
| 577 | ref ref return value truth match if $s->(@$c); |
| 578 | |
| 579 | |
| 580 | In reality, Table 1 covers 31 alternatives, because only the equality and |
| 581 | intersection tests are commutative; in all other cases, the roles of |
| 582 | the C<$s> and C<$c> variables could be reversed to produce a |
| 583 | different test. For example, instead of testing a single hash for |
| 584 | the existence of a series of keys (C<match if exists $s-E<gt>{$c}>), |
| 585 | one could test for the existence of a single key in a series of hashes |
| 586 | (C<match if exists $c-E<gt>{$s}>). |
| 587 | |
| 588 | As L<perltodo> observes, a Perl case mechanism must support all these |
| 589 | "ways to do it". |
| 590 | |
| 591 | |
| 592 | =head1 DESCRIPTION |
| 593 | |
| 594 | The Switch.pm module implements a generalized case mechanism that covers |
| 595 | the numerous possible combinations of switch and case values described above. |
| 596 | |
| 597 | The module augments the standard Perl syntax with two new control |
| 598 | statements: C<switch> and C<case>. The C<switch> statement takes a |
| 599 | single scalar argument of any type, specified in parentheses. |
| 600 | C<switch> stores this value as the |
| 601 | current switch value in a (localized) control variable. |
| 602 | The value is followed by a block which may contain one or more |
| 603 | Perl statements (including the C<case> statement described below). |
| 604 | The block is unconditionally executed once the switch value has |
| 605 | been cached. |
| 606 | |
| 607 | A C<case> statement takes a single scalar argument (in mandatory |
| 608 | parentheses if it's a variable; otherwise the parens are optional) and |
| 609 | selects the appropriate type of matching between that argument and the |
| 610 | current switch value. The type of matching used is determined by the |
| 611 | respective types of the switch value and the C<case> argument, as |
| 612 | specified in Table 1. If the match is successful, the mandatory |
| 613 | block associated with the C<case> statement is executed. |
| 614 | |
| 615 | In most other respects, the C<case> statement is semantically identical |
| 616 | to an C<if> statement. For example, it can be followed by an C<else> |
| 617 | clause, and can be used as a postfix statement qualifier. |
| 618 | |
| 619 | However, when a C<case> block has been executed control is automatically |
| 620 | transferred to the statement after the immediately enclosing C<switch> |
| 621 | block, rather than to the next statement within the block. In other |
| 622 | words, the success of any C<case> statement prevents other cases in the |
| 623 | same scope from executing. But see L<"Allowing fall-through"> below. |
| 624 | |
| 625 | Together these two new statements provide a fully generalized case |
| 626 | mechanism: |
| 627 | |
| 628 | use Switch; |
| 629 | |
| 630 | # AND LATER... |
| 631 | |
| 632 | %special = ( woohoo => 1, d'oh => 1 ); |
| 633 | |
| 634 | while (<>) { |
| 635 | switch ($_) { |
| 636 | |
| 74a6a946 |
637 | case (%special) { print "homer\n"; } # if $special{$_} |
| 638 | case /a-z/i { print "alpha\n"; } # if $_ =~ /a-z/i |
| 639 | case [1..9] { print "small num\n"; } # if $_ in [1..9] |
| 3ed9f206 |
640 | |
| 641 | case { $_[0] >= 10 } { # if $_ >= 10 |
| 642 | my $age = <>; |
| 643 | switch (sub{ $_[0] < $age } ) { |
| 644 | |
| 645 | case 20 { print "teens\n"; } # if 20 < $age |
| 646 | case 30 { print "twenties\n"; } # if 30 < $age |
| 647 | else { print "history\n"; } |
| 648 | } |
| 649 | } |
| 650 | |
| 651 | print "must be punctuation\n" case /\W/; # if $_ ~= /\W/ |
| 652 | } |
| 653 | |
| 654 | Note that C<switch>es can be nested within C<case> (or any other) blocks, |
| 655 | and a series of C<case> statements can try different types of matches |
| 656 | -- hash membership, pattern match, array intersection, simple equality, |
| 657 | etc. -- against the same switch value. |
| 658 | |
| 659 | The use of intersection tests against an array reference is particularly |
| 660 | useful for aggregating integral cases: |
| 661 | |
| 662 | sub classify_digit |
| 663 | { |
| 664 | switch ($_[0]) { case 0 { return 'zero' } |
| 665 | case [2,4,6,8] { return 'even' } |
| 666 | case [1,3,4,7,9] { return 'odd' } |
| 667 | case /[A-F]/i { return 'hex' } |
| 668 | } |
| 669 | } |
| 670 | |
| 671 | |
| 672 | =head2 Allowing fall-through |
| 673 | |
| 674 | Fall-though (trying another case after one has already succeeded) |
| 675 | is usually a Bad Idea in a switch statement. However, this |
| 676 | is Perl, not a police state, so there I<is> a way to do it, if you must. |
| 677 | |
| 678 | If a C<case> block executes an untargetted C<next>, control is |
| 679 | immediately transferred to the statement I<after> the C<case> statement |
| 680 | (i.e. usually another case), rather than out of the surrounding |
| 681 | C<switch> block. |
| 682 | |
| 683 | For example: |
| 684 | |
| 685 | switch ($val) { |
| 686 | case 1 { handle_num_1(); next } # and try next case... |
| 687 | case "1" { handle_str_1(); next } # and try next case... |
| 688 | case [0..9] { handle_num_any(); } # and we're done |
| 689 | case /\d/ { handle_dig_any(); next } # and try next case... |
| 690 | case /.*/ { handle_str_any(); next } # and try next case... |
| 691 | } |
| 692 | |
| 693 | If $val held the number C<1>, the above C<switch> block would call the |
| 694 | first three C<handle_...> subroutines, jumping to the next case test |
| 695 | each time it encountered a C<next>. After the thrid C<case> block |
| 696 | was executed, control would jump to the end of the enclosing |
| 697 | C<switch> block. |
| 698 | |
| 699 | On the other hand, if $val held C<10>, then only the last two C<handle_...> |
| 700 | subroutines would be called. |
| 701 | |
| 702 | Note that this mechanism allows the notion of I<conditional fall-through>. |
| 703 | For example: |
| 704 | |
| 705 | switch ($val) { |
| 706 | case [0..9] { handle_num_any(); next if $val < 7; } |
| 707 | case /\d/ { handle_dig_any(); } |
| 708 | } |
| 709 | |
| 710 | If an untargetted C<last> statement is executed in a case block, this |
| 711 | immediately transfers control out of the enclosing C<switch> block |
| 712 | (in other words, there is an implicit C<last> at the end of each |
| 713 | normal C<case> block). Thus the previous example could also have been |
| 714 | written: |
| 715 | |
| 716 | switch ($val) { |
| 717 | case [0..9] { handle_num_any(); last if $val >= 7; next; } |
| 718 | case /\d/ { handle_dig_any(); } |
| 719 | } |
| 720 | |
| 721 | |
| 722 | =head2 Automating fall-through |
| 723 | |
| 724 | In situations where case fall-through should be the norm, rather than an |
| 725 | exception, an endless succession of terminal C<next>s is tedious and ugly. |
| 726 | Hence, it is possible to reverse the default behaviour by specifying |
| 727 | the string "fallthrough" when importing the module. For example, the |
| 728 | following code is equivalent to the first example in L<"Allowing fall-through">: |
| 729 | |
| 730 | use Switch 'fallthrough'; |
| 731 | |
| 732 | switch ($val) { |
| 733 | case 1 { handle_num_1(); } |
| 734 | case "1" { handle_str_1(); } |
| 735 | case [0..9] { handle_num_any(); last } |
| 736 | case /\d/ { handle_dig_any(); } |
| 737 | case /.*/ { handle_str_any(); } |
| 738 | } |
| 739 | |
| 740 | Note the explicit use of a C<last> to preserve the non-fall-through |
| 741 | behaviour of the third case. |
| 742 | |
| 743 | |
| 744 | |
| 74a6a946 |
745 | =head2 Alternative syntax |
| 746 | |
| 747 | Perl 6 will provide a built-in switch statement with essentially the |
| 748 | same semantics as those offered by Switch.pm, but with a different |
| 693b9afd |
749 | pair of keywords. In Perl 6 C<switch> will be spelled C<given>, and |
| 74a6a946 |
750 | C<case> will be pronounced C<when>. In addition, the C<when> statement |
| 6596d39b |
751 | will not require switch or case values to be parenthesized. |
| 74a6a946 |
752 | |
| 6596d39b |
753 | This future syntax is also (largely) available via the Switch.pm module, by |
| 74a6a946 |
754 | importing it with the argument C<"Perl6">. For example: |
| 755 | |
| 756 | use Switch 'Perl6'; |
| 757 | |
| 758 | given ($val) { |
| 6596d39b |
759 | when 1 { handle_num_1(); } |
| 760 | when ($str1) { handle_str_1(); } |
| 761 | when [0..9] { handle_num_any(); last } |
| 762 | when /\d/ { handle_dig_any(); } |
| 763 | when /.*/ { handle_str_any(); } |
| 74a6a946 |
764 | } |
| 765 | |
| 6596d39b |
766 | Note that scalars still need to be parenthesized, since they would be |
| 767 | ambiguous in Perl 5. |
| 768 | |
| 769 | Note too that you can mix and match both syntaxes by importing the module |
| 74a6a946 |
770 | with: |
| 771 | |
| 772 | use Switch 'Perl5', 'Perl6'; |
| 773 | |
| 774 | |
| 3ed9f206 |
775 | =head2 Higher-order Operations |
| 776 | |
| 777 | One situation in which C<switch> and C<case> do not provide a good |
| 778 | substitute for a cascaded C<if>, is where a switch value needs to |
| 779 | be tested against a series of conditions. For example: |
| 780 | |
| 781 | sub beverage { |
| 782 | switch (shift) { |
| 783 | |
| 784 | case sub { $_[0] < 10 } { return 'milk' } |
| 785 | case sub { $_[0] < 20 } { return 'coke' } |
| 786 | case sub { $_[0] < 30 } { return 'beer' } |
| 787 | case sub { $_[0] < 40 } { return 'wine' } |
| 788 | case sub { $_[0] < 50 } { return 'malt' } |
| 789 | case sub { $_[0] < 60 } { return 'Moet' } |
| 790 | else { return 'milk' } |
| 791 | } |
| 792 | } |
| 793 | |
| 794 | The need to specify each condition as a subroutine block is tiresome. To |
| 795 | overcome this, when importing Switch.pm, a special "placeholder" |
| 796 | subroutine named C<__> [sic] may also be imported. This subroutine |
| 797 | converts (almost) any expression in which it appears to a reference to a |
| 798 | higher-order function. That is, the expression: |
| 799 | |
| 800 | use Switch '__'; |
| 801 | |
| 802 | __ < 2 + __ |
| 803 | |
| 804 | is equivalent to: |
| 805 | |
| 806 | sub { $_[0] < 2 + $_[1] } |
| 807 | |
| 808 | With C<__>, the previous ugly case statements can be rewritten: |
| 809 | |
| 810 | case __ < 10 { return 'milk' } |
| 811 | case __ < 20 { return 'coke' } |
| 812 | case __ < 30 { return 'beer' } |
| 813 | case __ < 40 { return 'wine' } |
| 814 | case __ < 50 { return 'malt' } |
| 815 | case __ < 60 { return 'Moet' } |
| 816 | else { return 'milk' } |
| 817 | |
| 818 | The C<__> subroutine makes extensive use of operator overloading to |
| 819 | perform its magic. All operations involving __ are overloaded to |
| 820 | produce an anonymous subroutine that implements a lazy version |
| 821 | of the original operation. |
| 822 | |
| 823 | The only problem is that operator overloading does not allow the |
| 824 | boolean operators C<&&> and C<||> to be overloaded. So a case statement |
| 825 | like this: |
| 826 | |
| 827 | case 0 <= __ && __ < 10 { return 'digit' } |
| 828 | |
| 829 | doesn't act as expected, because when it is |
| 830 | executed, it constructs two higher order subroutines |
| 831 | and then treats the two resulting references as arguments to C<&&>: |
| 832 | |
| 833 | sub { 0 <= $_[0] } && sub { $_[0] < 10 } |
| 834 | |
| 835 | This boolean expression is inevitably true, since both references are |
| 836 | non-false. Fortunately, the overloaded C<'bool'> operator catches this |
| 837 | situation and flags it as a error. |
| 838 | |
| 839 | =head1 DEPENDENCIES |
| 840 | |
| 841 | The module is implemented using Filter::Util::Call and Text::Balanced |
| 842 | and requires both these modules to be installed. |
| 843 | |
| 844 | =head1 AUTHOR |
| 845 | |
| 846 | Damian Conway (damian@conway.org) |
| 847 | |
| 848 | =head1 BUGS |
| 849 | |
| 850 | There are undoubtedly serious bugs lurking somewhere in code this funky :-) |
| 851 | Bug reports and other feedback are most welcome. |
| 852 | |
| d38ca171 |
853 | =head1 LIMITATION |
| 854 | |
| 855 | Due to the heuristic nature of Switch.pm's source parsing, the presence |
| 856 | of regexes specified with raw C<?...?> delimiters may cause mysterious |
| 857 | errors. The workaround is to use C<m?...?> instead. |
| 858 | |
| 3ed9f206 |
859 | =head1 COPYRIGHT |
| 860 | |
| 55a1c97c |
861 | Copyright (c) 1997-2001, Damian Conway. All Rights Reserved. |
| 862 | This module is free software. It may be used, redistributed |
| 863 | and/or modified under the same terms as Perl itself. |
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