Move parsers out of Parser.parse

parser.ml

@@ -92,41 +92,16 @@ let (@>) f g seq =
   let a, seq = f seq in
   g a seq
 
-(* parse tokens *)
-let parse ts =
-  (* value := int | ( expr ) *)
-  let rec value seq =
-    match seq () with
-    | Seq.Nil -> raise End_of_tokens
-    | Seq.Cons (x, seq) -> begin match x with
-        | Token.Int n -> Value (Int n), seq
-        | Float n -> Value (Float n), seq
-        | Ident id -> Var id, seq
-        | LParen -> expr seq
-        | _ -> unexpected_token x
-      end
+(* expr := "level" level_inner
+ *       | value binop_right
+*)
+let rec expr seq =
+  seq |> either
+    (ident "level" @> level_inner)
+    (value @> binop ~-1)
 
-  (* binop := binop op binop *)
-  and binop pre left seq =
-    match seq () with
-    | Seq.Nil -> left, Seq.empty
-    | Seq.Cons (x, seq) -> begin match x with
-        | op when token_is_operator op ->
-          let op = token_to_op op in
-          let o = precedence_of op in 
-          (* op has to be calculated first *)
-          if o > pre || op_is_right_to_left op && o = pre then
-            let v, seq = value seq in
-            let right, seq = binop o v seq in
-            binop pre (Ast.binop left op right) seq
-          else
-            left, Seq.cons x seq
-        | Token.RParen -> left, seq
-        | _ -> unexpected_token x
-      end
-
-  (* level_inner := "get" | "set" [op] *)
-  and level_inner _ seq =
+(* level_inner := "get" | "set" [op] *)
+and level_inner _ seq =
   let id, seq = idents (S.of_list ["get"; "set"]) seq in
   let op, seq = operator seq in
   if id = "get" then
@@ -137,14 +112,39 @@ let parse ts =
   else
     failwith "Parser.level"
 
-  (* expr := "level" level_inner
-   *       | value binop_right
-   *)
-  and expr seq =
-    seq |> either
-      (ident "level" @> level_inner)
-      (value @> binop ~-1)
-  in
+(* value := int | ( expr ) *)
+and value seq =
+  match seq () with
+  | Seq.Nil -> raise End_of_tokens
+  | Seq.Cons (x, seq) -> begin match x with
+      | Token.Int n -> Value (Int n), seq
+      | Float n -> Value (Float n), seq
+      | Ident id -> Var id, seq
+      | LParen -> expr seq
+      | _ -> unexpected_token x
+    end
+
+(* binop := binop op binop *)
+and binop pre left seq =
+  match seq () with
+  | Seq.Nil -> left, Seq.empty
+  | Seq.Cons (x, seq) -> begin match x with
+      | op when token_is_operator op ->
+        let op = token_to_op op in
+        let o = precedence_of op in
+        (* op has to be calculated first *)
+        if o > pre || (op_is_right_to_left op && o = pre) then
+          let v, seq = value seq in
+          let right, seq = binop o v seq in
+          binop pre (Ast.binop left op right) seq
+        else
+          left, Seq.cons x seq
+      | Token.RParen -> left, seq
+      | _ -> unexpected_token x
+    end
+
+(* parse tokens *)
+let parse ts =
   let ast, rest = expr ts in
   if rest () <> Seq.Nil then failwith "Parser.parse";
   ast