%{
  (* Exprpar.grm: parser specification for expression language   MRH 4/11 04 *)
  open Absyn;
%}

%token <int> INT
%token <string> VAR
%token LT CONJ DISJ NEGATION
%token PLUS MINUS TIMES EQ
%token END IN LET
%token IF THEN ELSE
%token LPAR RPAR
%token EOF

%left ELSE              /* lowest precedence  */
%left MINUS PLUS        /* middle precedence  */
%left TIMES             /* highest precedence */
%left DISJ
%left CONJ
%nonassoc NEGATION

%start Main
%type <int> Main
%type <Absyn.expr> Expr
%type <(string * Absyn.expr) list> DLIST
%type <Absyn.bexpr> BExpr

%%

Main:
    Expr EOF                            { eval $1 }
;

DLIST:
    /* empty string */                  { [] }
  | VAR EQ Expr DLIST                   { ($1, $3) :: $4 } 
;

BExpr:
    Expr LT Expr                        { Lt($1, $3)   } 
  | Expr EQ Expr                        { Eq($1, $3)   } 
  | BExpr CONJ BExpr                    { Conj($1, $3) } 
  | BExpr DISJ BExpr                    { Disj($1, $3) } 
  | NEGATION BExpr                      { Negation $2  } 
  | LPAR BExpr RPAR                     { $2 }

Expr:
    VAR                                 { Var $1  }
  | INT                                 { Int $1 }
  | MINUS Expr                          { Mminus $2 }
  | LPAR Expr RPAR                      { $2 }
  | LET DLIST IN Expr END               { Let($2, $4) }
  | Expr TIMES Expr                     { Times($1, $3) }  
  | Expr PLUS  Expr                     { Plus($1, $3) }  
  | Expr MINUS Expr                     { Minus($1, $3) } 
  | IF BExpr THEN Expr ELSE Expr        { Ite($2, $4, $6) } 
;