Add OCaml tutorial to the examples.

[oota-llvm.git] / examples / OCaml-Kaleidoscope / Chapter5 / parser.ml

diff --git a/examples/OCaml-Kaleidoscope/Chapter5/parser.ml b/examples/OCaml-Kaleidoscope/Chapter5/parser.ml
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+(*===---------------------------------------------------------------------===
+ * Parser
+ *===---------------------------------------------------------------------===*)
+
+(* binop_precedence - This holds the precedence for each binary operator that is
+ * defined *)
+let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
+
+(* precedence - Get the precedence of the pending binary operator token. *)
+let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
+
+(* primary
+ *   ::= identifier
+ *   ::= numberexpr
+ *   ::= parenexpr
+ *   ::= ifexpr
+ *   ::= forexpr *)
+let rec parse_primary = parser
+  (* numberexpr ::= number *)
+  | [< 'Token.Number n >] -> Ast.Number n
+
+  (* parenexpr ::= '(' expression ')' *)
+  | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
+
+  (* identifierexpr
+   *   ::= identifier
+   *   ::= identifier '(' argumentexpr ')' *)
+  | [< 'Token.Ident id; stream >] ->
+      let rec parse_args accumulator = parser
+        | [< e=parse_expr; stream >] ->
+            begin parser
+              | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
+              | [< >] -> e :: accumulator
+            end stream
+        | [< >] -> accumulator
+      in
+      let rec parse_ident id = parser
+        (* Call. *)
+        | [< 'Token.Kwd '(';
+             args=parse_args [];
+             'Token.Kwd ')' ?? "expected ')'">] ->
+            Ast.Call (id, Array.of_list (List.rev args))
+
+        (* Simple variable ref. *)
+        | [< >] -> Ast.Variable id
+      in
+      parse_ident id stream
+
+  (* ifexpr ::= 'if' expr 'then' expr 'else' expr *)
+  | [< 'Token.If; c=parse_expr;
+       'Token.Then ?? "expected 'then'"; t=parse_expr;
+       'Token.Else ?? "expected 'else'"; e=parse_expr >] ->
+      Ast.If (c, t, e)
+
+  (* forexpr
+        ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression *)
+  | [< 'Token.For;
+       'Token.Ident id ?? "expected identifier after for";
+       'Token.Kwd '=' ?? "expected '=' after for";
+       stream >] ->
+      begin parser
+        | [<
+             start=parse_expr;
+             'Token.Kwd ',' ?? "expected ',' after for";
+             end_=parse_expr;
+             stream >] ->
+            let step =
+              begin parser
+              | [< 'Token.Kwd ','; step=parse_expr >] -> Some step
+              | [< >] -> None
+              end stream
+            in
+            begin parser
+            | [< 'Token.In; body=parse_expr >] ->
+                Ast.For (id, start, end_, step, body)
+            | [< >] ->
+                raise (Stream.Error "expected 'in' after for")
+            end stream
+        | [< >] ->
+            raise (Stream.Error "expected '=' after for")
+      end stream
+
+  | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
+
+(* binoprhs
+ *   ::= ('+' primary)* *)
+and parse_bin_rhs expr_prec lhs stream =
+  match Stream.peek stream with
+  (* If this is a binop, find its precedence. *)
+  | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
+      let token_prec = precedence c in
+
+      (* If this is a binop that binds at least as tightly as the current binop,
+       * consume it, otherwise we are done. *)
+      if token_prec < expr_prec then lhs else begin
+        (* Eat the binop. *)
+        Stream.junk stream;
+
+        (* Parse the primary expression after the binary operator. *)
+        let rhs = parse_primary stream in
+
+        (* Okay, we know this is a binop. *)
+        let rhs =
+          match Stream.peek stream with
+          | Some (Token.Kwd c2) ->
+              (* If BinOp binds less tightly with rhs than the operator after
+               * rhs, let the pending operator take rhs as its lhs. *)
+              let next_prec = precedence c2 in
+              if token_prec < next_prec
+              then parse_bin_rhs (token_prec + 1) rhs stream
+              else rhs
+          | _ -> rhs
+        in
+
+        (* Merge lhs/rhs. *)
+        let lhs = Ast.Binary (c, lhs, rhs) in
+        parse_bin_rhs expr_prec lhs stream
+      end
+  | _ -> lhs
+
+(* expression
+ *   ::= primary binoprhs *)
+and parse_expr = parser
+  | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
+
+(* prototype
+ *   ::= id '(' id* ')' *)
+let parse_prototype =
+  let rec parse_args accumulator = parser
+    | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
+    | [< >] -> accumulator
+  in
+
+  parser
+  | [< 'Token.Ident id;
+       'Token.Kwd '(' ?? "expected '(' in prototype";
+       args=parse_args [];
+       'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
+      (* success. *)
+      Ast.Prototype (id, Array.of_list (List.rev args))
+
+  | [< >] ->
+      raise (Stream.Error "expected function name in prototype")
+
+(* definition ::= 'def' prototype expression *)
+let parse_definition = parser
+  | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
+      Ast.Function (p, e)
+
+(* toplevelexpr ::= expression *)
+let parse_toplevel = parser
+  | [< e=parse_expr >] ->
+      (* Make an anonymous proto. *)
+      Ast.Function (Ast.Prototype ("", [||]), e)
+
+(*  external ::= 'extern' prototype *)
+let parse_extern = parser
+  | [< 'Token.Extern; e=parse_prototype >] -> e