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

%%

stmt:
      %name IFTHEN
      IF expr THEN stmt
    | %name IFTHENELSE
      IF expr THEN stmt ELSE stmt
    | OTHERSTMT 
;
expr:
      EXPR 
;

%%