implement char escapes (elm-in-elm#20)

Author: aaronjanse

README.md

@@ -72,8 +72,8 @@ Oh God please yes! :heart: Feel free to look around the [<kbd>help wanted</kbd>]
 | ----------------- | -------------------- | -------------------- | ------------------ | ------------------ | -------------------- | ------------------ | ------------------ |
 | integers          | :heavy_check_mark:   | :heavy_check_mark:   | :heavy_check_mark: | :heavy_check_mark: | :warning: [[2]](#f2) | :heavy_check_mark: | :heavy_check_mark: |
 | floats            | :x: [[3]](#f3)       | :x: [[4]](#f4)       | :x: [[3]](#f3)     | :x: [[3]](#f3)     | :x: [[5]](#f5)       | :x: [[3]](#f3)     | :x: [[3]](#f3)     |
-| characters        | :warning: [[6]](#f6) | :warning: [[7]](#f7) | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark:   | :heavy_check_mark: | :heavy_check_mark: |
-| strings           | :warning: [[8]](#f8) | :warning: [[9]](#f9) | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark:   | :heavy_check_mark: | :heavy_check_mark: |
+| characters        | :heavy_check_mark:   | :heavy_check_mark:   | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark:   | :heavy_check_mark: | :heavy_check_mark: |
+| strings           | :warning: [[6]](#f6) | :warning: [[7]](#f7) | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark:   | :heavy_check_mark: | :heavy_check_mark: |
 | booleans          | :heavy_check_mark:   | :heavy_check_mark:   | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark:   | :heavy_check_mark: | :heavy_check_mark: |
 | variables         | :warning:            | :heavy_check_mark:   | :heavy_check_mark: | :heavy_check_mark: | :warning:            | :heavy_check_mark: | :heavy_check_mark: |
 | lists             | :x:                  | :x:                  | :x:                | :x:                | :x:                  | :x:                | :x:                |
@@ -98,10 +98,8 @@ Oh God please yes! :heart: Feel free to look around the [<kbd>help wanted</kbd>]
 3. <span id="f3"></span> Not implemented; tracked in [#17](https://github.com/elm-in-elm/compiler/issues/17)
 4. <span id="f4"></span> Not implemented; not tracked yet
 5. <span id="f5"></span> To be optimized the same way Ints are; not tracked yet
-6. <span id="f6"></span> Comprehensive tests missing; will be fixed in [#15](https://github.com/elm-in-elm/compiler/pull/15)
-7. <span id="f7"></span> Escape sequences not implemented; not tracked yet
-8. <span id="f8"></span> Comprehensive tests missing; tracked in [#21](https://github.com/elm-in-elm/compiler/issues/21)
-9. <span id="f9"></span> Multiline strings (and maybe more) missing; not tracked yet
+6. <span id="f6"></span> Comprehensive tests missing; not tracked yet
+7. <span id="f7"></span> Multiline strings (and maybe more) missing; not tracked yet
 
 ## Prerequisites
 
@@ -234,6 +232,12 @@ Make sure to format code before submitting a pull request!
         </br>
         <a href="https://github.com/Warry">Maxime Dantec</a>
       </td>
+      <td align="center">
+        <img width="150" height="150"
+        src="https://avatars0.githubusercontent.com/u/16829510">
+        </br>
+        <a href="https://github.com/aaronjanse">Aaron Janse</a>
+      </td>
     </tr>
   <tbody>
 </table>

src/compiler/Error.elm

@@ -80,6 +80,11 @@ type ParseProblem
     | ExpectingInt
     | ExpectingSingleQuote
     | ExpectingChar
+    | ExpectingEscapeBackslash
+    | ExpectingEscapeCharacter Char
+    | ExpectingUnicodeEscapeLeftBrace
+    | ExpectingUnicodeEscapeRightBrace
+    | InvalidUnicodeCodePoint
     | ExpectingDoubleQuote
     | ExpectingPlusOperator
     | ExpectingModuleDot -- `import Foo>.<Bar`

src/compiler/Stage/Parse/Parser.elm

@@ -428,22 +428,67 @@ literalInt =
         |> P.inContext InLiteralInt
 
 
-{-| TODO escapes
-TODO Unicode escapes
--}
+
+-- for literalChar and, in the future, literalString
+
+
+character =
+    P.oneOf
+        [ P.succeed identity
+            |. P.token (P.Token "\\" ExpectingEscapeBackslash)
+            |= P.oneOf
+                [ P.map (\_ -> '"') (P.token (P.Token "\"" (ExpectingEscapeCharacter '"'))) -- " (elm-vscode workaround)
+                , P.map (\_ -> '\'') (P.token (P.Token "'" (ExpectingEscapeCharacter '\'')))
+                , P.map (\_ -> '\n') (P.token (P.Token "n" (ExpectingEscapeCharacter 'n')))
+                , P.map (\_ -> '\t') (P.token (P.Token "t" (ExpectingEscapeCharacter 't')))
+                , P.map (\_ -> '\u{000D}') (P.token (P.Token "r" (ExpectingEscapeCharacter 'r')))
+                , P.succeed identity
+                    |. P.token (P.Token "u" (ExpectingEscapeCharacter 'u'))
+                    |. P.token (P.Token "{" ExpectingUnicodeEscapeLeftBrace)
+                    |= unicode
+                    |. P.token (P.Token "}" ExpectingUnicodeEscapeRightBrace)
+                ]
+        , P.succeed identity
+            |= P.getChompedString (P.chompIf (always True) ExpectingChar)
+            |> P.andThen
+                (\string ->
+                    string
+                        |> String.uncons
+                        |> Maybe.map (Tuple.first >> P.succeed)
+                        |> Maybe.withDefault (P.problem (CompilerBug "Multiple characters chomped in `character`"))
+                )
+        ]
+
+
 literalChar : Parser_ Literal
 literalChar =
     (P.succeed identity
         |. P.symbol (P.Token "'" ExpectingSingleQuote)
-        |= P.getChompedString (P.chompIf (always True) ExpectingChar)
+        |= character
         |. P.symbol (P.Token "'" ExpectingSingleQuote)
     )
+        |> P.map Char
+
+
+unicode : Parser_ Char
+unicode =
+    P.getChompedString (P.chompWhile Char.isHexDigit)
         |> P.andThen
-            (\string ->
-                string
-                    |> String.uncons
-                    |> Maybe.map (Tuple.first >> Char >> P.succeed)
-                    |> Maybe.withDefault (P.problem (CompilerBug "Multiple characters chomped in `literalChar`"))
+            (\str ->
+                let
+                    len =
+                        String.length str
+                in
+                if len < 4 || len > 6 then
+                    P.problem InvalidUnicodeCodePoint
+
+                else
+                    str
+                        |> String.toLower
+                        |> Hex.fromString
+                        |> Result.map Char.fromCode
+                        |> Result.map P.succeed
+                        |> Result.withDefault (P.problem InvalidUnicodeCodePoint)
             )
 
 

tests/ParserTest.elm

@@ -555,6 +555,37 @@ expr =
                   , "'A'"
                   , Ok (Literal (Char 'A'))
                   )
+
+                -- https://github.com/elm/compiler/blob/dcbe51fa22879f83b5d94642e117440cb5249bb1/compiler/src/Parse/String.hs#L279-L285
+                , ( "escape n"
+                  , "'\\n'"
+                  , Ok (Literal (Char '\n'))
+                  )
+                , ( "escape r"
+                  , "'\\r'"
+                  , Ok (Literal (Char '\u{000D}'))
+                  )
+                , ( "escape t"
+                  , "'\\t'"
+                  , Ok (Literal (Char '\t'))
+                  )
+                , ( "double quote"
+                  , "'\\\"'"
+                  , Ok (Literal (Char '"'))
+                    -- " (for vscode-elm bug)
+                  )
+                , ( "single quote"
+                  , "'\\''"
+                  , Ok (Literal (Char '\''))
+                  )
+                , ( "emoji"
+                  , "'😃'"
+                  , Ok (Literal (Char '😃'))
+                  )
+                , ( "escaped unicode code point"
+                  , "'\\u{1F648}'"
+                  , Ok (Literal (Char '🙈'))
+                  )
                 ]
               )
             , ( "literal string"