Implement syntax highlighter.

src/main/kotlin/gay/pizza/pork/main.kt

@@ -53,6 +53,9 @@ fun main(args: Array<String>) {
   if (program != parsedAst) {
     throw RuntimeException("Equality of parsed AST from printer was not proven.")
   }
+
+  val highlighter = Highlighter(AnsiHighlightScheme())
+  println(highlighter.highlight(stream).joinToString(""))
 }
 
 fun tokenize(input: String): TokenStream =

src/main/kotlin/gay/pizza/pork/parse/AnsiHighlightScheme.kt

@@ -0,0 +1,29 @@
+package gay.pizza.pork.parse
+
+open class AnsiHighlightScheme : HighlightScheme {
+  override fun highlight(token: Token): Highlight {
+    val attributes = when (token.type.family) {
+      TokenFamily.OperatorFamily -> operator()
+      TokenFamily.KeywordFamily -> keyword()
+      TokenFamily.SymbolFamily -> symbol()
+      TokenFamily.CommentFamily -> comment()
+      else -> null
+    }
+
+    return if (attributes != null) {
+      Highlight(token, ansi(attributes, token.text))
+    } else Highlight(token)
+  }
+
+  open fun operator(): AnsiAttributes = AnsiAttributes("32m")
+  open fun symbol(): AnsiAttributes = AnsiAttributes("33m")
+  open fun keyword(): AnsiAttributes = AnsiAttributes("35m")
+  open fun comment(): AnsiAttributes = AnsiAttributes("37m")
+
+  private fun ansi(attributes: AnsiAttributes, text: String): String =
+    "\u001b[${attributes.color}${text}\u001b[0m"
+
+  class AnsiAttributes(
+    val color: String
+  )
+}

src/main/kotlin/gay/pizza/pork/parse/Highlight.kt

@@ -0,0 +1,5 @@
+package gay.pizza.pork.parse
+
+class Highlight(val token: Token, val text: String? = null) {
+  override fun toString(): String = text ?: token.text
+}

src/main/kotlin/gay/pizza/pork/parse/HighlightScheme.kt

@@ -0,0 +1,5 @@
+package gay.pizza.pork.parse
+
+interface HighlightScheme {
+  fun highlight(token: Token): Highlight
+}

src/main/kotlin/gay/pizza/pork/parse/Highlighter.kt

@@ -1,19 +1,6 @@
 package gay.pizza.pork.parse
 
-abstract class Highlighter(source: TokenSource) : TokenProcessor(source) {
-  override fun process(token: Token) {
-    when {
-      token.type.keyword != null -> {
-        keyword(token)
-      }
-      token.type == TokenType.Symbol -> {
-        symbol(token)
-      }
-      else -> other(token)
-    }
-  }
-
-  abstract fun keyword(token: Token)
-  abstract fun symbol(token: Token)
-  abstract fun other(token: Token)
-}
+class Highlighter(val scheme: HighlightScheme) {
+  fun highlight(stream: TokenStream): List<Highlight> =
+    stream.tokens.map { scheme.highlight(it) }
+}

src/main/kotlin/gay/pizza/pork/parse/TokenFamily.kt

@@ -0,0 +1,10 @@
+package gay.pizza.pork.parse
+
+enum class TokenFamily : TokenTypeProperty {
+  OperatorFamily,
+  KeywordFamily,
+  SymbolFamily,
+  NumericLiteralFamily,
+  CommentFamily,
+  OtherFamily
+}

src/main/kotlin/gay/pizza/pork/parse/TokenProcessor.kt

@@ -1,15 +0,0 @@
-package gay.pizza.pork.parse
-
-abstract class TokenProcessor(val source: TokenSource) {
-  fun processAll() {
-    while (true) {
-      val token = source.next()
-      process(token)
-      if (token.type == TokenType.EndOfFile) {
-        break
-      }
-    }
-  }
-
-  abstract fun process(token: Token)
-}

src/main/kotlin/gay/pizza/pork/parse/TokenStream.kt

@@ -1,8 +1,5 @@
 package gay.pizza.pork.parse
 
 class TokenStream(val tokens: List<Token>) {
-  fun excludeAllWhitespace(): TokenStream =
-    TokenStream(tokens.filter { it.type != TokenType.Whitespace })
-
   override fun toString(): String = tokens.toString()
 }

src/main/kotlin/gay/pizza/pork/parse/TokenType.kt

@@ -1,39 +1,42 @@
 package gay.pizza.pork.parse
 
 import gay.pizza.pork.parse.TokenTypeProperty.*
+import gay.pizza.pork.parse.TokenFamily.*
 
 enum class TokenType(vararg properties: TokenTypeProperty) {
-  Symbol,
-  IntLiteral,
-  Equality,
-  Inequality,
+  Symbol(SymbolFamily),
+  IntLiteral(NumericLiteralFamily),
+  Equality(OperatorFamily),
+  Inequality(OperatorFamily),
   Equals(SingleChar('='), Promotion('=', Equality)),
-  Plus(SingleChar('+')),
-  Minus(SingleChar('-')),
-  Multiply(SingleChar('*')),
-  Divide(SingleChar('/')),
+  Plus(SingleChar('+'), OperatorFamily),
+  Minus(SingleChar('-'), OperatorFamily),
+  Multiply(SingleChar('*'), OperatorFamily),
+  Divide(SingleChar('/'), OperatorFamily),
   LeftCurly(SingleChar('{')),
   RightCurly(SingleChar('}')),
   LeftBracket(SingleChar('[')),
   RightBracket(SingleChar(']')),
   LeftParentheses(SingleChar('(')),
   RightParentheses(SingleChar(')')),
-  Negation(SingleChar('!'), Promotion('=', Inequality)),
+  Negation(SingleChar('!'), Promotion('=', Inequality), OperatorFamily),
   Comma(SingleChar(',')),
-  False(Keyword("false")),
-  True(Keyword("true")),
-  In(Keyword("in")),
-  If(Keyword("if")),
-  Then(Keyword("then")),
-  Else(Keyword("else")),
+  False(Keyword("false"), KeywordFamily),
+  True(Keyword("true"), KeywordFamily),
+  In(Keyword("in"), KeywordFamily),
+  If(Keyword("if"), KeywordFamily),
+  Then(Keyword("then"), KeywordFamily),
+  Else(Keyword("else"), KeywordFamily),
   Whitespace,
-  BlockComment,
-  LineComment,
+  BlockComment(CommentFamily),
+  LineComment(CommentFamily),
   EndOfFile;
 
   val promotions: List<Promotion> = properties.filterIsInstance<Promotion>()
   val keyword: Keyword? = properties.filterIsInstance<Keyword>().singleOrNull()
   val singleChar: SingleChar? = properties.filterIsInstance<SingleChar>().singleOrNull()
+  val family: TokenFamily =
+    properties.filterIsInstance<TokenFamily>().singleOrNull() ?: OtherFamily
 
   companion object {
     val Keywords = entries.filter { item -> item.keyword != null }

src/main/kotlin/gay/pizza/pork/parse/TokenTypeProperty.kt

@@ -1,7 +1,7 @@
 package gay.pizza.pork.parse
 
-sealed class TokenTypeProperty {
-  class SingleChar(val char: Char) : TokenTypeProperty()
-  class Promotion(val nextChar: Char, val type: TokenType) : TokenTypeProperty()
-  class Keyword(val text: String) : TokenTypeProperty()
+interface TokenTypeProperty {
+  class SingleChar(val char: Char) : TokenTypeProperty
+  class Promotion(val nextChar: Char, val type: TokenType) : TokenTypeProperty
+  class Keyword(val text: String) : TokenTypeProperty
 }