From 20e324f4c28c3d42f6a21f40138b22f32824f1af Mon Sep 17 00:00:00 2001
From: Hyeonung Baek <wiserlix@gmail.com>
Date: Tue, 18 Jan 2022 15:36:09 +0900
Subject: [PATCH] Improve operator lexing

---
 lex.ml    | 15 +++++++++++++++
 parser.ml | 20 ++++++++++++--------
 token.ml  | 15 ---------------
 3 files changed, 27 insertions(+), 23 deletions(-)

diff --git a/lex.ml b/lex.ml
index 4afdf46..48a6ad4 100644
--- a/lex.ml
+++ b/lex.ml
@@ -26,6 +26,21 @@ let is_ident_start =
 let is_ident =
   either is_ident_start is_digit
 
+let expect_token str tok seq =
+  let rec aux ts seq =
+    match ts (), seq () with
+    | Seq.Nil, _ -> Some seq
+    | Seq.Cons _, Seq.Nil -> None
+    | Seq.Cons (a, ts), Seq.Cons (b, seq) ->
+      if a = b then aux ts seq else None
+  in
+  let str = String.to_seq str in
+  aux str seq |> Option.map (fun s -> tok, s)
+
+let find_token seq =
+  !Token.tokens |> List.find_map
+    (fun (s, t) -> expect_token s t seq)
+
 (* same as take_while f seq, drop_while f seq *)
 let rec partition_while f seq : 'a Seq.t * 'a Seq.t =
   match seq () with
diff --git a/parser.ml b/parser.ml
index a68b223..c0a2552 100644
--- a/parser.ml
+++ b/parser.ml
@@ -31,14 +31,18 @@ let is_left_to_right = function
   | Add | Sub | Mul | Div -> true
   | _ -> assert false
 
-let token_to_op = function
-  | Token.Plus -> Add
-  | Minus -> Sub
-  | Asterisk -> Mul
-  | Slash -> Div
-  | Carret -> Exp
-  | Percent -> Mod
-  | _ -> failwith "Parser.token_to_op"
+let operators = [
+  Token.Plus, Add;
+  Minus, Sub;
+  Asterisk, Mul;
+  Slash, Div;
+  Carret, Exp;
+  Percent, Mod;
+] |> List.to_seq |> Hashtbl.of_seq
+
+let token_to_op tok =
+  try Hashtbl.find operators tok
+  with _ -> failwith "Parser.token_to_op"
 
 (* common parsers *)
 
diff --git a/token.ml b/token.ml
index 9a3e14c..1e83fc8 100644
--- a/token.ml
+++ b/token.ml
@@ -22,21 +22,6 @@ let tokens = ref [
   ")", RParen;
 ]
 
-let expect_token str tok seq =
-  let rec aux ts seq =
-    match ts (), seq () with
-    | Seq.Nil, _ -> Some seq
-    | Seq.Cons _, Seq.Nil -> None
-    | Seq.Cons (a, ts), Seq.Cons (b, seq) ->
-      if a = b then aux ts seq else None
-  in
-  let str = String.to_seq str in
-  aux str seq |> Option.map (fun s -> tok, s)
-
-let find_token seq =
-  !tokens |> List.find_map
-    (fun (s, t) -> expect_token s t seq)
-
 let to_string = function
   | Int n -> Printf.sprintf "[int: %d]" n
   | Float n -> Printf.sprintf "[float: %f]" n