%{
open LDText.Ast
open FSharp.Text.Lexing
%}

// tokens, used by lexer
%token <string> IDENTIFIER
%token LEFT_PAREN
%token RIGHT_PAREN
%token LEFT_BRACKET
%token RIGHT_BRACKET
%token COMMA
%token SEMICOLON
%token QUESTION_MARK
%token EOF

// start token
%start rung

// return type of parser, marked by start token
%type <Rung> rung

%%

rung:
  | steps SEMICOLON EOF { Rung $1 }

steps:
  | steps_reversed { List.rev $1 }

steps_reversed:
  | { [] }
  | steps_reversed instr { StepInstr $2 :: $1 }
  | steps_reversed branch { StepBranch $2 :: $1 }

branch:
  | LEFT_BRACKET branch_arms RIGHT_BRACKET { Branch $2 }

branch_arms:
  | branch_arms_reversed { List.rev $1 }

branch_arms_reversed:
  | { [] }
  | branch_arms_reversed COMMA steps { BranchArm $3 :: $1}
  | steps { [ BranchArm $1 ] }

instr:
  | IDENTIFIER LEFT_PAREN operands RIGHT_PAREN { { Op = $1; Args = $3 } }

operands:
  | operands_reversed { List.rev $1 }

operands_reversed:
  | { [] }
  | operands_reversed COMMA operand { $3 :: $1 }
  | operand { [ $1 ] }

operand:
  | IDENTIFIER { OperandTag $1 }
  | QUESTION_MARK { OperandHole }
%%