more work on the parser

lib/error.ml

@@ -4,15 +4,24 @@ type lexer_error = { pos : code_pos; msg : string }
 module LexerError = struct
   type t = lexer_error
 
-  let make (pos : code_pos) (msg : string) : lexer_error =
-    (* let pos = { line; col } in *)
-    { pos; msg }
+  let make (pos : code_pos) (msg : string) : lexer_error = { pos; msg }
 
   let print (e : lexer_error) =
     Printf.printf "LexerError at line %d, column %d: %s\n" e.pos.line e.pos.col e.msg
 end
 
-type lox_error = LexerError of lexer_error list
+type parser_error = { pos : code_pos; msg : string }
+
+module ParserError = struct
+  type t = parser_error
+
+  let make (pos : code_pos) (msg : string) : parser_error = { pos; msg }
+
+  let print (e : parser_error) =
+    Printf.printf "ParserError at line %d, column %d: %s\n" e.pos.line e.pos.col e.msg
+end
+
+type lox_error = LexerError of lexer_error list | ParserError of parser_error list
 
 let print_error (e : lox_error) =
   match e with
@@ -22,5 +31,12 @@ let print_error (e : lox_error) =
       Printf.printf "found %d %s:\n" num_errors
         (if num_errors = 1 then "LexerError" else "LexerErrors");
       List.iter LexerError.print es
+  | ParserError es ->
+      let num_errors = List.length es in
+      assert (num_errors != 0);
+      Printf.printf "found %d %s:\n" num_errors
+        (if num_errors = 1 then "ParserError" else "ParserErrors");
+      List.iter ParserError.print es
 
 let of_lexer_error e = Result.map_error (fun e -> LexerError e) e
+let of_parser_error e = Result.map_error (fun e -> ParserError e) e

lib/expr.ml

@@ -0,0 +1,36 @@
+type literal = String of string | Number of float | Bool of bool | Nil
+(* [@@deriving show { with_path = false }] *)
+
+let show_literal literal =
+  match literal with
+  | String s -> s
+  | Number x -> string_of_float x
+  | Bool b -> string_of_bool b
+  | Nil -> "nil"
+
+type binary_op = Plus | Minus | Mul | Div | Equal | Less | Greater | LessEqual | GreaterEqual
+[@@deriving show { with_path = false }]
+
+type unary_op = Neg | Not [@@deriving show { with_path = false }]
+
+type expr =
+  | Literal of literal
+  | BinaryExpr of { op : binary_op; left : expr; right : expr }
+  | UnaryExpr of { op : unary_op; expr : expr }
+(* [@@deriving show { with_path = false }] *)
+
+let rec show_expr ?(indent = 0) expr =
+  let show_indented = show_expr ~indent:(indent + 2) in
+  let ident_s = String.make indent ' ' in
+  match expr with
+  | Literal literal -> ident_s ^ show_literal literal
+  | BinaryExpr { op; left; right } ->
+      ident_s ^ show_binary_op op ^ "\n" ^ show_indented left ^ "\n" ^ show_indented right
+  | UnaryExpr { op; expr } -> ident_s ^ show_unary_op op ^ "\n" ^ show_indented expr
+
+let make_string (s : string) = Literal (String s)
+let make_number (x : float) = Literal (Number x)
+let make_bool (b : bool) = Literal (Bool b)
+let make_nil () = Literal Nil
+let make_binary (op : binary_op) (left : expr) (right : expr) = BinaryExpr { op; left; right }
+let make_unary (op : unary_op) (expr : expr) = UnaryExpr { op; expr }

lib/lexer.ml

@@ -56,7 +56,7 @@ type state = {
 }
 
 module State = struct
-  type t = state
+  (* type t = state *)
 
   let is_digit c = match c with '0' .. '9' -> true | _ -> false
   let is_alpha c = match c with 'a' .. 'z' | 'A' .. 'Z' -> true | _ -> false
@@ -95,10 +95,6 @@ module State = struct
     | Some c when f c -> advance_while f (snd (advance state))
     | _ -> state (* EOF or no match *)
 
-  let last_char (state : state) : char =
-    assert (state.cur_pos > 0);
-    state.source.[state.cur_pos - 1]
-
   let append_token (pos : code_pos) (token_type : token_type) (state : state) : state =
     (* let pos = { line = state.line; col = state.col } in *)
     { state with tokens_rev = { token_type; pos } :: state.tokens_rev }
@@ -208,5 +204,6 @@ let tokenize (source : string) : lexer_result =
       { source; start_pos = 0; cur_pos = 0; tokens_rev = []; errors_rev = []; line = 1; col = 0 }
   in
   (* reverse the reversed tokens/errors *)
-  if List.length state.errors_rev = 0 then Ok (List.rev state.tokens_rev)
-  else Error (List.rev state.errors_rev)
+  (* if List.length state.errors_rev = 0 then Ok (List.rev state.tokens_rev)
+     else Error (List.rev state.errors_rev) *)
+  match state.errors_rev with [] -> Ok (List.rev state.tokens_rev) | es -> Error (List.rev es)

lib/lexer.mli

@@ -0,0 +1,85 @@
+type token_type =
+  | LeftParen
+  | RightParen
+  | LeftBrace
+  | RightBrace
+  | Plus
+  | Minus
+  | Star
+  | Slash
+  | Bang
+  | Dot
+  | Comma
+  | Semicolon
+  | Equal
+  | EqualEqual
+  | BangEqual
+  | Greater
+  | Less
+  | GreaterEqual
+  | LessEqual
+  | Identifier of string
+  | String of string
+  | Number of float
+  | And
+  | Class
+  | Else
+  | False
+  | Fun
+  | For
+  | If
+  | Nil
+  | Or
+  | Print
+  | Return
+  | Super
+  | This
+  | True
+  | Var
+  | While
+  | Comment of string
+  | Eof
+
+val pp_token_type : Format.formatter -> token_type -> unit
+val show_token_type : token_type -> string
+val keywords : (string, token_type) Hashtbl.t
+
+type token = { token_type : token_type; pos : Error.code_pos }
+
+val show_token : token -> string
+
+type lexer_result = (token list, Error.lexer_error list) result
+
+(* type state = {
+        source : string;
+        start_pos : int;
+        cur_pos : int;
+        tokens_rev : token list;
+        errors_rev : Error.lexer_error list;
+        line : int;
+        col : int;
+      }
+   module State : sig
+     type t = state
+
+     val is_digit : char -> bool
+     val is_alpha : char -> bool
+     val is_alphanum : char -> bool
+     val is_identifier : char -> bool
+     val is_at_end : state -> bool
+     val get_lexeme : state -> int -> int -> string
+     val advance : state -> char * state
+     val peek : state -> char option
+     val advance_if : char -> state -> bool * state
+     val advance_until : char -> state -> bool * state
+     val advance_while : (char -> bool) -> state -> state
+     val last_char : state -> char
+     val append_token : Error.code_pos -> token_type -> state -> state
+     val append_error : Error.code_pos -> string -> state -> state
+     val parse_number : state -> state
+     val parse_keyword_or_identifier : state -> state
+     val parse_block_commend : state -> state
+     val tokenize_rec : state -> state
+   end *)
+
+val tokenize : string -> lexer_result

lib/lox.ml

@@ -1,7 +1,9 @@
 let ( let* ) = Result.bind
 
-module Lexer = Lexer
 module Error = Error
+module Expr = Expr
+module Lexer = Lexer
+module Parser = Parser
 
 type token = Lexer.token
 type lox_error = Error.lox_error
@@ -13,6 +15,8 @@ let run (source : string) : (unit, lox_error) result =
   Printf.printf "Got %d tokens\n" (List.length tokens);
   List.iter f tokens;
   print_endline "";
+  let* expr = Error.of_parser_error (Parser.parse tokens) in
+  Printf.printf "%s\n" (Expr.show_expr expr);
   Ok ()
 
 let runRepl () : unit =

lib/parser.ml

@@ -0,0 +1,137 @@
+open Error
+open Expr
+open Lexer
+
+type parse_result = (expr, parser_error list) result
+type state = { tokens : token list; errors_rev : parser_error list }
+
+module State = struct
+  let is_at_end state = (List.hd state.tokens).token_type == Eof
+
+  let append_error msg pos state =
+    let e = { pos; msg } in
+    { state with errors_rev = e :: state.errors_rev }
+
+  let advance state = { state with tokens = List.tl state.tokens }
+  let peek state = List.hd state.tokens
+
+  let next state =
+    assert (not ((List.hd state.tokens).token_type == Eof));
+    (List.hd state.tokens, advance state)
+
+  let advance_if state tt =
+    if (peek state).token_type == tt then (true, advance state) else (false, state)
+
+  let matches state tts =
+    let f = ( == ) (peek state).token_type in
+    List.fold_left (fun acc tt -> acc || f tt) false tts
+
+  let collect_chain (state : state) (tts : token_type list) higher_prec :
+      (expr * token) array * state =
+    (* ([], state) *)
+    let state_ref = ref state in
+    let out_list_rev = ref [] in
+    while (not (is_at_end !state_ref)) && matches !state_ref tts do
+      let token, state = next !state_ref in
+      let expr, state = higher_prec state in
+      state_ref := state;
+      out_list_rev := (expr, token) :: !out_list_rev
+    done;
+    (Array.of_list (List.rev !out_list_rev), !state_ref)
+
+  let mul_or_div (state : state) : expr * state =
+    let token, state = next state in
+    (make_string @@ show_token_type token.token_type, state)
+
+  let sum_or_diff (state : state) : expr * state =
+    let expr, state = mul_or_div state in
+    (* if (not (is_at_end state)) && matches state [ Plus; Minus ] then
+         let token, state = next state in
+         let expr2, state = sum_or_diff state in
+         let (op : binary_op) =
+           match token.token_type with
+           | Plus -> Plus
+           | Minus -> Minus
+           | _ -> assert false (* should only be here if tt is + - *)
+         in
+         let expr = make_binary op expr expr2 in
+         (expr, state)
+       else (expr, state) *)
+    (* turn expr and state to refs for the loop *)
+    (* Printf.printf "expr: %s\n\n" (show_expr expr);
+       let expr_ref, state_ref = (ref expr, ref state) in
+       while (not (is_at_end !state_ref)) && matches !state_ref [ Plus; Minus ] do
+         let token, state = next !state_ref in
+         let expr2, state = mul_or_div state in
+         let (op : binary_op) =
+           match token.token_type with
+           | Plus -> Plus
+           | Minus -> Minus
+           | _ -> assert false (* should only be here if tt is + - *)
+         in
+         let expr = make_binary op !expr_ref expr2 in
+         (* (expr_ref, state_ref) := (expr, state) *)
+         Printf.printf "expr: %s\n\n" (show_expr expr);
+         expr_ref := expr;
+         state_ref := state
+       done;
+       (!expr_ref, !state_ref) *)
+    let exprs_tokens, state = collect_chain state [ Plus; Minus ] mul_or_div in
+    let f acc (expr, token) =
+      let op : binary_op =
+        match token.token_type with Plus -> Plus | Minus -> Minus | _ -> assert false
+      in
+      make_binary op acc expr
+    in
+    let expr = Array.fold_left f expr exprs_tokens in
+    (expr, state)
+
+  let rec inequality (state : state) : expr * state =
+    let expr, state = sum_or_diff state in
+    if (not (is_at_end state)) && matches state [ Greater; GreaterEqual; Less; LessEqual ] then
+      let token, state = next state in
+      let expr2, state = inequality state in
+      (* TODO: maybe rework to only have Less and Greater as ops; performance? *)
+      let (op : binary_op) =
+        match token.token_type with
+        | Greater -> Greater
+        | Less -> Less
+        | GreaterEqual -> GreaterEqual
+        | LessEqual -> LessEqual
+        | _ -> assert false (* should only be here if tt is > < >= <= *)
+      in
+      let expr = make_binary op expr expr2 in
+      (expr, state)
+    else (expr, state)
+
+  let rec equality (state : state) : expr * state =
+    let expr, state = inequality state in
+    if matches state [ EqualEqual; BangEqual ] then
+      let token, state = next state in
+      let expr2, state = equality state in
+      let expr =
+        match token.token_type with
+        | EqualEqual -> make_binary Equal expr expr2
+        | BangEqual ->
+            let expr = make_binary Equal expr expr2 in
+            make_unary Not expr
+        | _ -> assert false (* should only be here if tt is == != *)
+      in
+      (expr, state)
+    else (expr, state)
+
+  let expression (state : state) : expr * state = equality state
+end
+
+let parse (tokens : token list) : parse_result =
+  let state = { tokens; errors_rev = [] } in
+  let expr, state = State.expression state in
+  let state =
+    if not (State.is_at_end state) then
+      let tt = (State.peek state).token_type in
+      let msg = Printf.sprintf "Unexpected %s at end" (show_token_type tt) in
+      State.append_error msg (State.peek state).pos state
+    else state
+  in
+  (* if List.length state.errors_rev != 0 then Ok expr else Error (List.rev state.errors_rev) *)
+  match state.errors_rev with [] -> Ok expr | es -> Error (List.rev es)