mlyacc/examples/calc/calc.grm

   1 (* Sample interactive calculator for ML-Yacc *)
   2
   3 fun lookup "bogus" = 10000
   4   | lookup s = 0
   5
   6 %%
   7
   8 %eop EOF SEMI
   9
  10 (* %pos declares the type of positions for terminals.
  11    Each symbol has an associated left and right position. *)
  12
  13 %pos int
  14
  15 %left SUB PLUS
  16 %left TIMES DIV
  17 %right CARAT
  18
  19 %term ID of string | NUM of int | PLUS | TIMES | PRINT |
  20       SEMI | EOF | CARAT | DIV | SUB
  21 %nonterm EXP of int | START of int option
  22
  23 %name Calc
  24
  25 %subst PRINT for ID
  26 %prefer PLUS TIMES DIV SUB
  27 %keyword PRINT SEMI
  28
  29 %noshift EOF
  30 %value ID ("bogus")
  31 %verbose
  32 %%
  33
  34 (* the parser returns the value associated with the expression *)
  35
  36   START : PRINT EXP (print (Int.toString EXP);
  37                      print "\n";
  38                      SOME EXP)
  39         | EXP (SOME EXP)
  40         | (NONE)
  41   EXP : NUM             (NUM)
  42       | ID              (lookup ID)
  43       | EXP PLUS EXP    (EXP1+EXP2)
  44       | EXP TIMES EXP   (EXP1*EXP2)
  45       | EXP DIV EXP     (EXP1 div EXP2)
  46       | EXP SUB EXP     (EXP1-EXP2)
  47       | EXP CARAT EXP   (let fun e (m,0) = 1
  48                                 | e (m,l) = m*e(m,l-1)
  49                          in e (EXP1,EXP2)
  50                          end)