I am writing my first Ocamllex and Ocamlyacc program by following this tutorial
My dune file looks like
(executable
(public_name Calculator)
(name main))
(ocamllex lexer)
(ocamlyacc parser)
My lexer.mll file is
{
open Parser
}
rule read = parse
| eof { EOF }
And parser.mly file is
%token EOF
%start <unit> prog
%%
prog:
| EOF { () }
;
My main.ml file is
type expr = unit
(** [parse s] parses string [s] into an AST. *)
let parse (s: string): expr =
let lexbuf = Lexing.from_string s in
let ast = Parser.prog Lexer.read lexbuf in
ast
(** [interp s] interprets [s] by Lexing and parsing it,
evaluating it, and converting the result into string *)
let interp (s: string) : string =
failwith "unimplemented"
When I say dune build I just get an error
File "bin/parser.mly", line 3: syntax error
%start <unit> prog
However the tutorial I am following (linked above) the same code compiles and runs. and it shows how to parse and empty string. I don't know much about this error because its not tell me what the syntax error is. I have written the code exactly as shown in the video.
I think ocamlyacc doesn’t have that %start <type> symbol syntax. You should separately specify the type using %type:
%type <unit> prog
%start prog