%{
=head1 SYNOPSIS

This grammar deals with the famous ambiguous PL/I phrase:

                if then=if then if=then

The (partial) solution uses C<YYExpect> in the lexical analyzer to predict the token
that fulfills the parser expectatives.

Compile it with:

               eyapp -C PL_I_conflictWithLexical.eyp

Run it with:

               ./PL_I_conflictWithLexical.pm -t -c 'if if=then then then=if'

for more detail:

               ./PL_I_conflictWithLexical.pm -deb -t -c 'if if=then then then=if'

and also

               ./PL_I_conflictWithLexical.pm -t -i -c 'if then=if then if=then'

Also try:

                ./PL_I_conflictWithLexical.pm -t -c 'if then=if then if a=b then c=d'

=cut

%}

%strict

%token then =  { $self->expects('then') and /\Gthen\b/gc     and return ('then', 'then'); }
%token if   =  { $self->expects('if')   and /\Gif(?!\s*=)/gc and return ('if', 'if'); }
%token ID  = /([a-zA-Z_]\w*)/

%tree bypass
%%
stmt: 
    ifstmt 
  | assignstmt
;

ifstmt: 
     %name IF
    if expr then stmt
;

assignstmt: 
    %name ASSIGN
    id '=' expr
;

expr:
    %name EQ
    id '=' id
  | id
;

id: 
    %name ID
    ID
;

%%