module FRIST-SYNTAX

  imports BOOL

  syntax Expr ::= Expr "+" Expr [left, strict]
                | "(" Expr ")" [bracket]
                | Ident

  syntax Ident ::= "x" | "y" | "z"

endmodule

module FRIST

  imports FRIST-SYNTAX

  rule X + Y => Y + X [anywhere]

  rule X + (Y + Z) => (X + Y) + Z [anywhere]

  rule (X + Y) + Z => X + (Y + Z) [anywhere]

endmodule



# kompile frist.k
[WARNING] Running as root is not recommended
File "realdef.ml", line 629, characters 289-296:
Error: This variant expression is expected to have type bool
       The constructor KApply1 does not belong to type bool
[Error] Critical: ocamlopt returned nonzero exit code: 2
Examine output to see errors.