mirror of
https://github.com/MorizzG/MLox.git
synced 2025-12-06 04:22:41 +00:00
reworked parser error handling
now based around result; since each parsing step can emit at most one error until synchronisation is triggered we can store the errors in the result. also state is now stored in a ref variable. the copy-and-update is more pure, but really messes up the let* expression for the expr/error results.
This commit is contained in:
parent
f14677b6f5
commit
485ecebdf3
1 changed files with 164 additions and 148 deletions
312
lib/parser.ml
312
lib/parser.ml
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@ -1,167 +1,183 @@
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let ( let* ) = Result.bind
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open Error
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open Error
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open Expr
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open Expr
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open Lexer
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open Lexer
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type parse_result = (expr, parser_error list) result
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type parse_result = (expr, parser_error list) result
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type expr_result = (expr, parser_error) result
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type state = { tokens : token list; errors_rev : parser_error list }
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type state = { tokens : token list; errors_rev : parser_error list }
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module State = struct
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let is_at_end state = (List.hd !state.tokens).token_type == Eof
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let is_at_end state = (List.hd state.tokens).token_type == Eof
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let append_error msg pos state =
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let append_error msg pos state =
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let e = { pos; msg } in
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let e = { pos; msg } in
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{ state with errors_rev = e :: state.errors_rev }
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{ state with errors_rev = e :: state.errors_rev }
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let advance state = { state with tokens = List.tl state.tokens }
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let advance state = state := { !state with tokens = List.tl !state.tokens }
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let peek state = List.hd state.tokens
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let peek state = List.hd !state.tokens
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let next state =
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let next state =
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assert (not ((List.hd state.tokens).token_type == Eof));
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assert (not ((List.hd !state.tokens).token_type == Eof));
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(List.hd state.tokens, advance state)
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let token = List.hd !state.tokens in
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advance state;
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token
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let advance_if state tt =
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let advance_if state tt =
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if (peek state).token_type == tt then (true, advance state) else (false, state)
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if (peek state).token_type == tt then (
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advance state;
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true)
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else false
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let consume state tt =
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let matches state tts =
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if (peek state).token_type == tt then advance state
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let f = ( == ) (peek state).token_type in
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Array.fold_left (fun acc tt -> acc || f tt) false tts
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let cur_pos state = (peek state).pos
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let collect_chain (state : state ref) (tts : token_type array)
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(higher_prec : state ref -> expr_result) : ((expr * token) array, parser_error) result =
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(* ([], state) *)
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(* let out_list_rev = ref [] in
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while (not (is_at_end state)) && matches state tts do
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let token = next state in
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let expr = higher_prec state in
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out_list_rev := (expr, token) :: !out_list_rev
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done;
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Ok (Array.of_list (List.rev !out_list_rev)) *)
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let rec collect_chain_rec (acc : (expr * token) list) =
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if (not (is_at_end state)) && matches state tts then
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let token = next state in
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let* expr = higher_prec state in
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let acc = (expr, token) :: acc in
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collect_chain_rec acc
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else Ok acc
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in
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(* match collect_chain_rec [] with Ok l -> Ok (Array.of_list (List.rev l)) | Error e -> Error e *)
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collect_chain_rec [] |> Result.map (fun l -> Array.of_list (List.rev l))
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let primary (state : state ref) : expr_result =
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match (peek state).token_type with
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| Number x -> Ok (make_number x)
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| String s -> Ok (make_string s)
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| True -> Ok (make_bool true)
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| False -> Ok (make_bool false)
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| Nil -> Ok (make_nil ())
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| tt ->
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let msg = Printf.sprintf "Unexpected %s, expected valid expression" (show_token_type tt) in
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let pos = (peek state).pos in
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Error { msg; pos }
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let rec grouping (state : state ref) : expr_result =
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if matches state [| LeftParen |] then (
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advance state;
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let* expr = expression state in
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if advance_if state RightParen then Ok expr
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else
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else
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let state =
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let pos = cur_pos state in
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append_error
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let tt = (peek state).token_type in
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(Printf.sprintf "Unexpected %s, expected %s"
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let msg = Printf.sprintf "Expected RightParen, got %s instead" (show_token_type tt) in
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(show_token_type (peek state).token_type)
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Error { pos; msg })
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(show_token_type tt))
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else primary state
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(peek state).pos state
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in
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state
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let matches state tts =
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and neg_not (state : state ref) : expr_result =
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let f = ( == ) (peek state).token_type in
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if matches state [| Bang; Minus |] then
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Array.fold_left (fun acc tt -> acc || f tt) false tts
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let token = next state in
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let* expr = neg_not state in
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let collect_chain (state : state) (tts : token_type array) higher_prec :
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let op =
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(expr * token) array * state =
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(* ([], state) *)
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let state_ref = ref state in
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let out_list_rev = ref [] in
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while (not (is_at_end !state_ref)) && matches !state_ref tts do
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let token, state = next !state_ref in
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let expr, state = higher_prec state in
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state_ref := state;
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out_list_rev := (expr, token) :: !out_list_rev
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done;
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(Array.of_list (List.rev !out_list_rev), !state_ref)
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let primary (state : state) : expr * state =
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match (peek state).token_type with
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| Number x -> (make_number x, advance state)
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| String s -> (make_string s, advance state)
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| True -> (make_bool true, advance state)
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| False -> (make_bool false, advance state)
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| Nil -> (make_nil (), advance state)
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| tt ->
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( make_nil (),
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append_error
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(Printf.sprintf "Unexpected %s, expected valid expression" (show_token_type tt))
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(peek state).pos state )
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let rec grouping (state : state) : expr * state =
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if matches state [| LeftParen |] then
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let state = advance state in
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let expr, state = expression state in
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let state = consume state RightParen in
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(expr, state)
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else primary state
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and neg_not (state : state) : expr * state =
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if matches state [| Bang; Minus |] then
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let token, state = next state in
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let expr, state = neg_not state in
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let op =
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match token.token_type with
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| Bang -> Not
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| Minus -> Neg
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| _ -> assert false (* should only be here if tt is - ! *)
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in
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let expr = make_unary op expr in
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(expr, state)
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else grouping state
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and mul_or_div (state : state) : expr * state =
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let expr, state = neg_not state in
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let exprs_tokens, state = collect_chain state [| Star; Slash |] neg_not in
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let f acc (expr, token) =
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let op : binary_op =
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match token.token_type with
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| Star -> Mul
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| Slash -> Div
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| _ -> assert false (* should only be here if tt is * / *)
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in
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make_binary op acc expr
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in
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let expr = Array.fold_left f expr exprs_tokens in
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(expr, state)
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and sum_or_diff (state : state) : expr * state =
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let expr, state = mul_or_div state in
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let exprs_tokens, state = collect_chain state [| Plus; Minus |] mul_or_div in
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let f acc (expr, token) =
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let op : binary_op =
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match token.token_type with
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| Plus -> Plus
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| Minus -> Minus
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| _ -> assert false (* should only be here if tt is + - *)
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in
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make_binary op acc expr
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in
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let expr = Array.fold_left f expr exprs_tokens in
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(expr, state)
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and inequality (state : state) : expr * state =
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(* TODO: maybe rework to only have Less and Greater as ops; performance? *)
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let expr, state = sum_or_diff state in
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let exprs_tokens, state =
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collect_chain state [| Greater; GreaterEqual; Less; LessEqual |] sum_or_diff
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in
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let f acc (expr, token) =
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let (op : binary_op) =
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match token.token_type with
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| Greater -> Greater
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| Less -> Less
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| GreaterEqual -> GreaterEqual
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| LessEqual -> LessEqual
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| _ -> assert false (* should only be here if tt is > < >= <= *)
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in
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make_binary op acc expr
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in
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let expr = Array.fold_left f expr exprs_tokens in
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(expr, state)
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and equality (state : state) : expr * state =
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let expr, state = inequality state in
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let exprs_tokens, state = collect_chain state [| EqualEqual; BangEqual |] inequality in
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let f acc (expr, token) =
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match token.token_type with
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match token.token_type with
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| EqualEqual -> make_binary Equal acc expr
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| Bang -> Not
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| BangEqual ->
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| Minus -> Neg
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let expr = make_binary Equal acc expr in
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| _ -> assert false (* should only be here if tt is - ! *)
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make_unary Not expr
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| _ -> assert false (* should only be here if tt is == != *)
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in
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in
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let expr = Array.fold_left f expr exprs_tokens in
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let expr = make_unary op expr in
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(expr, state)
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Ok expr
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else grouping state
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and expression (state : state) : expr * state = equality state
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and mul_or_div (state : state ref) : expr_result =
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end
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let* expr = neg_not state in
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let* exprs_tokens = collect_chain state [| Star; Slash |] neg_not in
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let f acc (expr, token) =
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let op : binary_op =
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match token.token_type with
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| Star -> Mul
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| Slash -> Div
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| _ -> assert false (* should only be here if tt is * / *)
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in
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make_binary op acc expr
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in
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let expr = Array.fold_left f expr exprs_tokens in
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Ok expr
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and sum_or_diff (state : state ref) : expr_result =
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let* expr = mul_or_div state in
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let* exprs_tokens = collect_chain state [| Plus; Minus |] mul_or_div in
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let f acc (expr, token) =
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let op : binary_op =
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match token.token_type with
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| Plus -> Plus
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| Minus -> Minus
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| _ -> assert false (* should only be here if tt is + - *)
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in
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make_binary op acc expr
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in
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let expr = Array.fold_left f expr exprs_tokens in
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Ok expr
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and inequality (state : state ref) : expr_result =
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(* TODO: maybe rework to only have Less and Greater as ops; performance? *)
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let* expr = sum_or_diff state in
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let* exprs_tokens =
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collect_chain state [| Greater; GreaterEqual; Less; LessEqual |] sum_or_diff
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in
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let f acc (expr, token) =
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let (op : binary_op) =
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match token.token_type with
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| Greater -> Greater
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| Less -> Less
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| GreaterEqual -> GreaterEqual
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| LessEqual -> LessEqual
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| _ -> assert false (* should only be here if tt is > < >= <= *)
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in
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make_binary op acc expr
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in
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let expr = Array.fold_left f expr exprs_tokens in
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Ok expr
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and equality (state : state ref) : expr_result =
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let* expr = inequality state in
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let* exprs_tokens = collect_chain state [| EqualEqual; BangEqual |] inequality in
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let f acc (expr, token) =
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match token.token_type with
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| EqualEqual -> make_binary Equal acc expr
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| BangEqual ->
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let expr = make_binary Equal acc expr in
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make_unary Not expr
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| _ -> assert false (* should only be here if tt is == != *)
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in
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let expr = Array.fold_left f expr exprs_tokens in
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Ok expr
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and expression (state : state ref) : expr_result = equality state
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let rec synchronise (state : state ref) =
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match (peek state).token_type with
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| Semicolon -> advance state
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| Class | Fun | Var | For | If | While | Print | Return | Eof -> ()
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| _ ->
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advance state;
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synchronise state
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let parse (tokens : token list) : parse_result =
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let parse (tokens : token list) : parse_result =
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let state = { tokens; errors_rev = [] } in
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let state = ref { tokens; errors_rev = [] } in
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let expr, state = State.expression state in
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expression state |> Result.map_error (fun e -> [ e ])
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let state =
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(* let expr = State.expression state in
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if not (State.is_at_end state) then
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let state =
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let tt = (State.peek state).token_type in
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if not (State.is_at_end state) then
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let msg = Printf.sprintf "Unexpected %s at end" (show_token_type tt) in
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let tt = (State.peek state).token_type in
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State.append_error msg (State.peek state).pos state
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let msg = Printf.sprintf "Unexpected %s at end" (show_token_type tt) in
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else state
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State.append_error msg (State.peek state).pos state
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in
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else state
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(* if List.length state.errors_rev != 0 then Ok expr else Error (List.rev state.errors_rev) *)
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in
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match state.errors_rev with [] -> Ok expr | es -> Error (List.rev es)
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(* if List.length state.errors_rev != 0 then Ok expr else Error (List.rev state.errors_rev) *)
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match state.errors_rev with [] -> Ok expr | es -> Error (List.rev es) *)
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