(*===---------------------------------------------------------------------===
* 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
* ::= varexpr *)
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
(* varexpr
* ::= 'var' identifier ('=' expression?
* (',' identifier ('=' expression)?)* 'in' expression *)
| [< 'Token.Var;
(* At least one variable name is required. *)
'Token.Ident id ?? "expected identifier after var";
init=parse_var_init;
var_names=parse_var_names [(id, init)];
(* At this point, we have to have 'in'. *)
'Token.In ?? "expected 'in' keyword after 'var'";
body=parse_expr >] ->
Ast.Var (Array.of_list (List.rev var_names), body)
| [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
(* unary
* ::= primary
* ::= '!' unary *)
and parse_unary = parser
(* If this is a unary operator, read it. *)
| [< 'Token.Kwd op when op != '(' && op != ')'; operand=parse_expr >] ->
Ast.Unary (op, operand)
(* If the current token is not an operator, it must be a primary expr. *)
| [< stream >] -> parse_primary stream
(* 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_unary 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
and parse_var_init = parser
(* read in the optional initializer. *)
| [< 'Token.Kwd '='; e=parse_expr >] -> Some e
| [< >] -> None
and parse_var_names accumulator = parser
| [< 'Token.Kwd ',';
'Token.Ident id ?? "expected identifier list after var";
init=parse_var_init;
e=parse_var_names ((id, init) :: accumulator) >] -> e
| [< >] -> accumulator
(* expression
* ::= primary binoprhs *)
and parse_expr = parser
| [< lhs=parse_unary; stream >] -> parse_bin_rhs 0 lhs stream
(* prototype
* ::= id '(' id* ')'
* ::= binary LETTER number? (id, id)
* ::= unary LETTER number? (id) *)
let parse_prototype =
let rec parse_args accumulator = parser
| [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
| [< >] -> accumulator
in
let parse_operator = parser
| [< 'Token.Unary >] -> "unary", 1
| [< 'Token.Binary >] -> "binary", 2
in
let parse_binary_precedence = parser
| [< 'Token.Number n >] -> int_of_float n
| [< >] -> 30
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))
| [< (prefix, kind)=parse_operator;
'Token.Kwd op ?? "expected an operator";
(* Read the precedence if present. *)
binary_precedence=parse_binary_precedence;
'Token.Kwd '(' ?? "expected '(' in prototype";
args=parse_args [];
'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
let name = prefix ^ (String.make 1 op) in
let args = Array.of_list (List.rev args) in
(* Verify right number of arguments for operator. *)
if Array.length args != kind
then raise (Stream.Error "invalid number of operands for operator")
else
if kind == 1 then
Ast.Prototype (name, args)
else
Ast.BinOpPrototype (name, args, binary_precedence)
| [< >] ->
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