%{
  (* Exprpar.grm: parser specification for the simple expression language *)

  open Absyn;
%}

%token <int> CSTINT
%token <string> NAME
%token PLUS MINUS TIMES EQ
%token END IN LET
%token LPAR RPAR
%token EOF

%left MINUS PLUS        /* lowest precedence  */
%left TIMES             /* highest precedence */

%start Main
%type <Absyn.expr> Main Expr

%%

Main:
    Expr EOF                            { $1 }
;

Expr:
    NAME                                { Var $1  }
  | CSTINT                              { CstI $1 }
  | MINUS CSTINT                        { CstI (~ $2) }
  | LPAR Expr RPAR                      { $2 }
  | LET NAME EQ Expr IN Expr END        { Let($2, $4, $6) }
  | Expr TIMES Expr                     { Prim("*", [$1, $3]) }  
  | Expr PLUS  Expr                     { Prim("+", [$1, $3]) }  
  | Expr MINUS Expr                     { Prim("-", [$1, $3]) } 
;