Código de CalcSimple.eyp

pl@nereida:~/LEyapp/examples$ cat -n CalcSimple.eyp
 1  # CalcSimple.eyp
 2  %right  '='
 3  %left   '-' '+'
 4  %left   '*' '/'
 5  %left   NEG
 6  %right  '^'
 7  %{
 8  my %s;
 9  %}
10
11  %%
12  start: input { [ $_[1], \%s] }
13  ;
14
15  input:
16      /* empty */     { [] }
17    | input line  { push(@{$_[1]},$_[2]) if defined($_[2]); $_[1] }
18  ;
19
20  line:
21    '\n'         { undef }
22    | $exp '\n'  { print "$exp\n"; $exp }
23    | error '\n' { $_[0]->YYErrok; undef }
24  ;
25
26  exp:
27      NUM
28    | $VAR                    { $s{$VAR} }
29    | VAR.x '=' exp.y         { $s{$x} = $y }
30    | exp.x '+' exp.y         { $x + $y }
31    | exp.x '-' exp.y         { $x - $y }
32    | exp.x '*' exp.y         { $x * $y }
33    | exp.x '^' exp.y         { $x ** $y }
34    | exp.x '/' exp.y
35      {
36        my $parser = shift;
37
38             $y and return($x / $y);
39         $parser->YYData->{ERRMSG}
40           =   "Illegal division by zero.\n";
41         $parser->YYError;
42         undef
43      }
44    |   '-' $exp %prec NEG
45      { -$exp }
46    |   '(' $exp ')'
47      { $exp }
48  ;
49
50  %%
51
52  sub _Error {
53    my $private = $_[0]->YYData;
54
55        exists $private->{ERRMSG}
56    and do {
57        print $private->{ERRMSG};
58        delete $private->{ERRMSG};
59        return;
60    };
61    print "Syntax error.\n";
62  }
63
64  my $input;
65
66  sub _Lexer {
67    my($parser)=shift;
68
69    # topicalize $input
70    for ($input) {
71      s/^[ \t]//;      # skip whites
72      return('',undef) unless $_;
73      return('NUM',$1) if s{^([0-9]+(?:\.[0-9]+)?)}{};
74      return('VAR',$1) if s/^([A-Za-z][A-Za-z0-9_]*)//;
75      return($1,$1)    if s/^(.)//s;
76    }
77
78    return('',undef);
79  }
80
81  sub Run {
82      my($self)=shift;
83
84      $input = shift;
85      return $self->YYParse( yylex => \&_Lexer, yyerror => \&_Error,
86                             #yydebug => 0xF
87                           );
88  }