example parsing string to AST

.ocamlformat

@@ -0,0 +1 @@
+margin=100

bin/main.ml

@@ -1,4 +1,9 @@
-open Flan
+open Flan.Parse
 
 let () =
-  Example.print_greeting "mate"
+  let source_str = Flan.Examples.let_bind_int in
+  let lexbuf = Lexing.from_string source_str in
+  Printf.printf "Convert source \"%s\" ->\n" source_str;
+  match parse_program lexbuf with
+  | Ok ast -> print_ast ast
+  | Error msg -> print_endline ("ERROR: \n" ^ msg)

dune-project

@@ -1,4 +1,5 @@
 (lang dune 3.15)
+(using menhir 3.0)
 
 (name flan)
 
@@ -19,7 +20,7 @@
  (name flan)
  (synopsis "A short synopsis")
  (description "A longer description")
- (depends ocaml dune)
+ (depends ocaml dune menhir)
  (tags
   (topics "to describe" your project)))
 

flan.opam

@@ -12,6 +12,7 @@ bug-reports: "https://github.com/username/reponame/issues"
 depends: [
   "ocaml"
   "dune" {>= "3.15"}
+  "menhir"
   "odoc" {with-doc}
 ]
 build: [

lib/dune

@@ -1,2 +1,7 @@
 (library
  (name flan))
+
+(menhir
+ (modules oflan))
+
+(ocamllex olexer)

lib/example.ml

@@ -1 +0,0 @@
-let print_greeting name = print_endline ("G'day, " ^ name)

lib/examples.ml

@@ -0,0 +1,4 @@
+(** Examples of syntax / programs as strings that can be imported and tested *)
+
+let let_bind_int = "let x = 10"
+let let_bind_str = "let s = \"hello\" "

lib/oflan.mly

@@ -0,0 +1,42 @@
+/* Declarations */
+
+%{
+  open Omniflan.Ast
+%}
+
+%token Eof
+%token Newline
+%token Let
+
+%token False
+%token True
+%token <string> Ident
+%token <int> Int
+%token <float> F32
+
+%token Equal
+%token LParen
+%token RParen
+
+%start <Omniflan.Ast.program> prog
+
+%%
+/* Grammar */
+
+expr:
+  | i = Int; { Int i }
+
+stmt:
+  | Let; var_name = Ident; Equal; bound_expr = expr
+    { Let { 
+        loc = $startpos;
+        var_name = var_name;
+        bindee = bound_expr 
+      } 
+    }
+
+toplevel_item:
+  | stmt = stmt { Stmt stmt }
+
+prog:
+  | prog = separated_list(Newline, toplevel_item); Eof { prog }

lib/olexer.mll

@@ -0,0 +1,35 @@
+{
+  open Lexing
+  open Oflan
+
+  exception SyntaxError of string
+
+  let next_line lexbuf =
+    let pos = lexbuf.lex_curr_p in
+    lexbuf.lex_curr_p <-
+      { pos with pos_bol = lexbuf.lex_curr_pos;
+                pos_lnum = pos.pos_lnum + 1
+      }
+}
+
+let digit = ['0'-'9']
+let digits =  digit*
+let alpha = ['a'-'z' 'A'-'Z']
+let ident = (alpha) (alpha|digit|'_')* (* regex for identifier *)
+let whitespace = [' ' '\t']+
+let newline = '\r' | '\n' | "\r\n"
+
+let int = digits
+
+rule read =
+  parse
+  | whitespace { read lexbuf }
+  | newline { next_line lexbuf; read lexbuf }
+  | int { Int (int_of_string (Lexing.lexeme lexbuf))}
+  | "let" { Let }
+  | ident { Ident (Lexing.lexeme lexbuf) }
+  | '=' { Equal }
+  | '(' { LParen }
+  | 'R' { RParen }
+  | eof { Eof }
+  | _ { raise (SyntaxError ("Unexpected char: " ^ Lexing.lexeme lexbuf)) }

lib/omniflan.ml

@@ -1,22 +1,29 @@
+(*
+Notes
 
-type binary_opt =
+For now everything will be split into modules inside this one big file while prototyping.
-  | Add
+*)
-  | Subtract
-  | Multiply
-  | Divide
 
-type expr =
+module Ast = struct
-  | Let of { name: string; bindee: expr }
+  type loc = Lexing.position
-  | Binary of { lhs: expr; rhs: expr; operator: binary_opt }
+  type unary_op = Negate
-  | IfElse of { condition: expr }
+  type binary_op = Add | Subtract | Multiply | Divide
+  type literal = Int of int
 
-type builtin_type =
+  type expr = Int of int
-  | I32
+  (* | Literal of literal *)
-  | F32
+  (* | BinaryOp of { lhs: expr; rhs: expr; operator: binary_op } *)
-  | Bool
+  (* | IfElse of { condition: expr; if_expr: expr; else_expr: expr } *)
-  | Char
 
-module Examples = struct
+  and stmt =
-  let let_bind_int = "let x = 10"
+    | Let of { loc : loc; var_name : string; bindee : expr } (* Let binding "let x = 5" *)
-  let let_bind_str = "let s = \"hello\" "
+    | FuncDecl (* TODO: arguments *)
+
+  and toplevel_item = Stmt of stmt
+
+  type builtin_type = I32 | F32 | Bool | Char
+  type program = toplevel_item list
 end
+
+module Typer = struct end
+(** This module helps take an untyped AST and produce a typed AST *)

lib/parse.ml

@@ -0,0 +1,31 @@
+open Lexing
+
+exception SyntaxError of string
+
+(* Prints the line number and character number where the error occurred.*)
+let print_error_position lexbuf =
+  let pos = lexbuf.lex_curr_p in
+  Printf.sprintf "Line:%d Position:%d" pos.pos_lnum (pos.pos_cnum - pos.pos_bol + 1)
+
+let parse_program lexbuf =
+  try Ok (Oflan.prog Olexer.read lexbuf) with
+  | SyntaxError msg ->
+      let error_msg = Printf.sprintf "%s: %s\n" (print_error_position lexbuf) msg in
+      Error error_msg
+  | Oflan.Error ->
+      let error_msg = Printf.sprintf "%s: syntax error\n" (print_error_position lexbuf) in
+      Error error_msg
+
+open Omniflan.Ast
+
+let string_of_expr expr = match expr with Int i -> "Int " ^ string_of_int i
+
+let string_of_stmt stmt =
+  match stmt with
+  | Let s -> Printf.sprintf "(%d) Let %s = %s" s.loc.pos_lnum s.var_name (string_of_expr s.bindee)
+  | FuncDecl -> failwith "TODO"
+
+let print_ast prog =
+  List.iter
+    (fun toplevel -> match toplevel with Stmt stmt -> print_endline (string_of_stmt stmt))
+    prog