Start making generated parser

ldtext/Parser.fsy

@@ -0,0 +1,38 @@
+%{
+open LDText.Ast
+// helper functions
+%}
+
+// start token
+%start start
+
+// 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
+
+// return type of parser, marked by start token
+%type <Rung option> rung
+
+%%
+
+start:
+  | instr EOF { $1 }
+
+instr:
+  | IDENTIFIER LEFT_PAREN operands RIGHT_PAREN { StepInstr { Op = $1; Args = [ $3 ] } }
+
+operands:
+  | { }
+  | operand operands { $1; $2 }
+
+operand:
+  | IDENTIFIER { OperandTag $1 }
+  | QUESTION_MARK { OperandHole }
+%%