Change Lexer to use a data structure for tokens

lib/lexer.ex

@@ -1,6 +1,12 @@
 defmodule MfmParser.Lexer do
   alias MfmParser.Reader
 
+  alias MfmParser.Token
+  alias MfmParser.Token.MFMOpen
+  alias MfmParser.Token.MFMClose
+  alias MfmParser.Token.Newline
+  alias MfmParser.Token.Text
+
   def peek(input) do
     case next(input) do
       {:ok, token, _} -> {:ok, token}
@@ -9,34 +15,44 @@ defmodule MfmParser.Lexer do
   end
 
   def next(input) do
-    recursive_next(Reader.next(input), "", type_of_token(input))
+    recursive_extract_next_token(Reader.next(input), get_empty_token(input))
   end
 
-  defp recursive_next(:eof, _, _) do
+  defp recursive_extract_next_token(:eof, _) do
     :eof
   end
 
-  defp recursive_next({:ok, char, rest}, part, token_type) do
-    if is_end_of_token?(char, rest, token_type) do
-      {:ok, part <> char, rest}
+  defp recursive_extract_next_token({:ok, char, rest}, token) do
+    if is_last_char_of_token?(char, rest, token) do
+      {:ok, token |> Token.append(char), rest}
     else
-      recursive_next(Reader.next(rest), part <> char, token_type)
+      recursive_extract_next_token(Reader.next(rest), token |> Token.append(char))
     end
   end
 
-  defp is_end_of_token?(char, _, :mfm_open) do
-    char in [" "]
+  defp get_empty_token(input) do
+    case Reader.peek(input) do
+      :eof -> :eof
+      {:ok, "$"} -> %MFMOpen{}
+      {:ok, "]"} -> %MFMClose{}
+      {:ok, "\n"} -> %Newline{}
+      _ -> %Text{}
+    end
   end
 
-  defp is_end_of_token?(_, _, :mfm_close) do
+  defp is_last_char_of_token?(char, _, %MFMOpen{}) do
+    char == " "
+  end
+
+  defp is_last_char_of_token?(_, _, %MFMClose{}) do
     true
   end
 
-  defp is_end_of_token?(_, _, :newline) do
+  defp is_last_char_of_token?(_, _, %Newline{}) do
     true
   end
 
-  defp is_end_of_token?(_, rest, :text) do
+  defp is_last_char_of_token?(_, rest, %Text{}) do
     case Reader.next(rest) do
       :eof -> true
       {:ok, "]", _} -> true
@@ -44,14 +60,4 @@ defmodule MfmParser.Lexer do
       _ -> false
     end
   end
-
-  defp type_of_token(input) do
-    case Reader.peek(input) do
-      :eof -> :eof
-      {:ok, "$"} -> :mfm_open
-      {:ok, "]"} -> :mfm_close
-      {:ok, "\n"} -> :newline
-      _ -> :text
-    end
-  end
 end

lib/token.ex

@@ -0,0 +1,5 @@
+defmodule MfmParser.Token do
+  def append(token = %{content: content}, new_char) do
+    token |> Map.put(:content, content <> new_char)
+  end
+end

lib/token/mfm_close.ex

@@ -0,0 +1,3 @@
+defmodule MfmParser.Token.MFMClose do
+   defstruct content: ""
+end

lib/token/mfm_open.ex

@@ -0,0 +1,3 @@
+defmodule MfmParser.Token.MFMOpen do
+   defstruct content: ""
+end

lib/token/newline.ex

@@ -0,0 +1,3 @@
+defmodule MfmParser.Token.Newline do
+   defstruct content: ""
+end

lib/token/text.ex

@@ -0,0 +1,3 @@
+defmodule MfmParser.Token.Text do
+   defstruct content: ""
+end

test/lexer_test.exs

@@ -1,7 +1,13 @@
 defmodule MfmParser.LexerTest do
   use ExUnit.Case
+
   alias MfmParser.Lexer
 
+  alias MfmParser.Token.MFMOpen
+  alias MfmParser.Token.MFMClose
+  alias MfmParser.Token.Newline
+  alias MfmParser.Token.Text
+
   describe "eof" do
     test "peek/1 handles eof" do
       assert Lexer.peek("") == :eof
@@ -14,9 +20,11 @@ defmodule MfmParser.LexerTest do
 
   describe "mfm $[ token" do
     test "it ends with a space" do
-      assert Lexer.peek("$[ola puerca]") == {:ok, "$[ola "}
-      assert Lexer.next("$[ola puerca]") == {:ok, "$[ola ", "puerca]"}
-      assert Lexer.next("$[ola.x,speed=5s puerca]") == {:ok, "$[ola.x,speed=5s ", "puerca]"}
+      assert Lexer.peek("$[ola puerca]") == {:ok, %MFMOpen{content: "$[ola "}}
+      assert Lexer.next("$[ola puerca]") == {:ok, %MFMOpen{content: "$[ola "}, "puerca]"}
+
+      assert Lexer.next("$[ola.x,speed=5s puerca]") ==
+               {:ok, %MFMOpen{content: "$[ola.x,speed=5s "}, "puerca]"}
     end
 
     test "it doesn't crash if the token can't be completed" do
@@ -27,54 +35,54 @@ defmodule MfmParser.LexerTest do
 
   describe "] token" do
     test "it handles ] as a token" do
-      assert Lexer.peek("]ve anime") == {:ok, "]"}
-      assert Lexer.next("]ve anime") == {:ok, "]", "ve anime"}
+      assert Lexer.peek("]ve anime") == {:ok, %MFMClose{content: "]"}}
+      assert Lexer.next("]ve anime") == {:ok, %MFMClose{content: "]"}, "ve anime"}
     end
 
     test "it works at the eof" do
-      assert Lexer.peek("]") == {:ok, "]"}
-      assert Lexer.next("]") == {:ok, "]", ""}
+      assert Lexer.peek("]") == {:ok, %MFMClose{content: "]"}}
+      assert Lexer.next("]") == {:ok, %MFMClose{content: "]"}, ""}
     end
   end
 
   describe "text token" do
     test "it ends when a mfm token opens while a $ alone doesn't end the text token" do
       assert Lexer.peek("Tu abuela ve anime y no se lava el $[spin culo]") ==
-               {:ok, "Tu abuela ve anime y no se lava el "}
+               {:ok, %Text{content: "Tu abuela ve anime y no se lava el "}}
 
       assert Lexer.next("Tu abuela ve anime y no se lava el $[spin culo]") ==
-               {:ok, "Tu abuela ve anime y no se lava el ", "$[spin culo]"}
+               {:ok, %Text{content: "Tu abuela ve anime y no se lava el "}, "$[spin culo]"}
 
-      assert Lexer.peek("A $2 chocolatine") == {:ok, "A $2 chocolatine"}
-      assert Lexer.next("A $2 chocolatine") == {:ok, "A $2 chocolatine", ""}
+      assert Lexer.peek("A $2 chocolatine") == {:ok, %Text{content: "A $2 chocolatine"}}
+      assert Lexer.next("A $2 chocolatine") == {:ok, %Text{content: "A $2 chocolatine"}, ""}
 
-      assert Lexer.peek("Eyes like $$") == {:ok, "Eyes like $$"}
-      assert Lexer.next("Eyes like $$") == {:ok, "Eyes like $$", ""}
+      assert Lexer.peek("Eyes like $$") == {:ok, %Text{content: "Eyes like $$"}}
+      assert Lexer.next("Eyes like $$") == {:ok, %Text{content: "Eyes like $$"}, ""}
     end
 
     test "it ends when a mfm token closes" do
-      assert Lexer.peek("el culo]") == {:ok, "el culo"}
-      assert Lexer.next("el culo]") == {:ok, "el culo", "]"}
+      assert Lexer.peek("el culo]") == {:ok, %Text{content: "el culo"}}
+      assert Lexer.next("el culo]") == {:ok, %Text{content: "el culo"}, "]"}
     end
 
     test "it ends when the eof is reached" do
       assert Lexer.peek("Tu abuela ve anime y no se lava el culo") ==
-               {:ok, "Tu abuela ve anime y no se lava el culo"}
+               {:ok, %Text{content: "Tu abuela ve anime y no se lava el culo"}}
 
       assert Lexer.next("Tu abuela ve anime y no se lava el culo") ==
-               {:ok, "Tu abuela ve anime y no se lava el culo", ""}
+               {:ok, %Text{content: "Tu abuela ve anime y no se lava el culo"}, ""}
     end
   end
 
   describe "newline token" do
     test "it handles \n as a token" do
-      assert Lexer.peek("\nchocolat") == {:ok, "\n"}
-      assert Lexer.next("\nchocolat") == {:ok, "\n", "chocolat"}
+      assert Lexer.peek("\nchocolat") == {:ok, %Newline{content: "\n"}}
+      assert Lexer.next("\nchocolat") == {:ok, %Newline{content: "\n"}, "chocolat"}
     end
 
     test "it works at the eof" do
-      assert Lexer.peek("\n") == {:ok, "\n"}
-      assert Lexer.next("\n") == {:ok, "\n", ""}
+      assert Lexer.peek("\n") == {:ok, %Newline{content: "\n"}}
+      assert Lexer.next("\n") == {:ok, %Newline{content: "\n"}, ""}
     end
   end
 end

test/token_test.exs

@@ -0,0 +1,9 @@
+defmodule MfmParser.TokenTest do
+  use ExUnit.Case
+
+  alias MfmParser.Token
+
+  test "it appends a character to the content" do
+    assert %{content: "$[p"} = Token.append(%{content: "$["}, "p")
+  end
+end