64 lines
1.4 KiB
Elixir
64 lines
1.4 KiB
Elixir
defmodule MfmParser.Lexer do
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alias MfmParser.Reader
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alias MfmParser.Token
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alias MfmParser.Token.MFMOpen
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alias MfmParser.Token.MFMClose
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alias MfmParser.Token.Newline
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alias MfmParser.Token.Text
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def peek(input) do
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case next(input) do
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{:ok, token, _} -> {:ok, token}
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:eof -> :eof
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end
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end
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def next(input) do
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recursive_extract_next_token(Reader.next(input), get_empty_token(input))
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end
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defp recursive_extract_next_token(:eof, _) do
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:eof
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end
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defp recursive_extract_next_token({:ok, char, rest}, token) do
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if is_last_char_of_token?(char, rest, token) do
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{:ok, token |> Token.append(char), rest}
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else
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recursive_extract_next_token(Reader.next(rest), token |> Token.append(char))
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end
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end
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defp get_empty_token(input) do
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case Reader.peek(input) do
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:eof -> :eof
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{:ok, "$"} -> %MFMOpen{}
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{:ok, "]"} -> %MFMClose{}
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{:ok, "\n"} -> %Newline{}
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_ -> %Text{}
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end
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end
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defp is_last_char_of_token?(char, _, %MFMOpen{}) do
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char == " "
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end
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defp is_last_char_of_token?(_, _, %MFMClose{}) do
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true
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end
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defp is_last_char_of_token?(_, _, %Newline{}) do
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true
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end
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defp is_last_char_of_token?(_, rest, %Text{}) do
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case Reader.next(rest) do
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:eof -> true
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{:ok, "]", _} -> true
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{:ok, "$", new_rest} -> Reader.peek(new_rest) == {:ok, "["}
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_ -> false
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end
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end
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end
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