/*
$ eyapp -C dummytoken.eyp 
$ ./dummytoken.pm -t -i --dot t.png -m 1 -c 'if e then if e then o else o'

IFTHEN(
  TERMINAL[e],
  IFTHENELSE(
    TERMINAL[e],
    TERMINAL[o],
    TERMINAL[o]
  )
)
Also have a look at the t.png output file

The following execution gives an error:

$ ./dummytoken.pm -c 'TUTU'

*/
%syntactic token IF        = /(?i:if)/
%syntactic token ELSE      = /(?i:else)/
%syntactic token THEN      = /(?i:then)/
%token EXPR      = /(?i:(e))/
%token OTHERSTMT = /(?i:(o))/

# A dummy token is never generated by the lexical analyzer
%dummy token TUTU

%left TUTU
%left ELSE

%tree bypass
%%
stmt:
          %name IFTHEN
          IF expr THEN stmt %prec TUTU
        | %name IFTHENELSE
          IF expr THEN stmt ELSE stmt
        | OTHERSTMT
        | TUTU  # will be rejected. The input 'TUTU' produces an error, since the token isn't generated
        ;
expr: 
       EXPR
    ;
   
%%