%{
  (* WHILEpar.grm: parser specification for a simple WHILE language *)

  open Absyn;

%}

%token <int> INT
%token <string> VAR
%token TRUE FALSE
%token PLUS MINUS TIMES EQ LT
%token NEG AND
%token ASS SKIP SEMI IF THEN ELSE WHILE DO
%token LPAR RPAR
%token EOF

%left SEMI             /* lowest precedence  */
%left AND               
%nonassoc NEG 
%left LE EQ             
%left MINUS PLUS       
%left TIMES             /* highest precedence */
%nonassoc HIGHEST

%start Main
%type <Absyn.aExp> AExp
%type <Absyn.bExp> BExp
%type <Absyn.stm> Main Stm

%%

Main:
    Stm EOF                            { $1 }
;

Stm:
    VAR ASS AExp                              { <-($1,$3) }
  | SKIP                                      { Skip     }
  | LPAR Stm RPAR                             { $2 }
  | Stm SEMI Stm                              { ^^($1,$3) }
  | IF BExp THEN Stm ELSE Stm  %prec HIGHEST  { ITE($2,$4,$6) }
  | WHILE BExp DO Stm          %prec HIGHEST  { While($2,$4) }
;
    
AExp:
    VAR                                 { V $1  }
  | INT                                 { N $1 }
  | LPAR AExp RPAR                      { $2 }
  | AExp PLUS  AExp                     { ++($1,$3) } 
  | AExp TIMES AExp                     { **($1,$3) }  
  | AExp MINUS AExp                     { --($1,$3) } 
;

BExp:
    TRUE                                 { TT }
  | FALSE                                { FF }
  | AExp EQ AExp                         { ==($1,$3) } 
  | AExp LT AExp                         { <<($1,$3) } 
  | LPAR BExp RPAR                       { $2 }
  | NEG BExp                             { !! $2 } 
  | BExp AND BExp                        { &&($1,$3) }  
;