Ambiguous parsing

[egormkn]

Problem I found a bug in lama parser, that is somehow connected to ambiguous grammar rules for case expression and infix operators.

Example code

infix | at ++ (lhs, rhs) {
  lhs ++ rhs
}

infix -> at ++ (lhs, rhs) {
  lhs ++ rhs
}

(* Prints "WAT" *)
printf ("%s\n", 
  case "?" of
    "?" -> "W" 
  | "A" -> "T"
  esac.string
);

(* Prints W *)
printf ("%s\n", 
  case "?" of
    "?" -> "W" 
  | "A" -> "T"
  esac
)

Expected behaviour Both outputs are quite reasonable but they should be the same for both expressions.

Environment

• lamac: v1.0 (Version master, e4b34a3ec, Sat Mar 21 13:05:14 2020 +0300)
• ostap: v0.4 (https://github.com/dboulytchev/ostap/commit/6565c87a643318f4182f810518c94ae7208fc074)

[dboulytchev]

https://github.com/JetBrains-Research/Lama/issues/5#issuecomment-600263002