Implement token promotion.

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

@@ -1,5 +1,5 @@
 package gay.pizza.pork.ast
 
-class BooleanLiteral(val value: Boolean) : Expression {
+class BooleanLiteral(val value: Boolean) : Expression() {
   override val type: NodeType = NodeType.BooleanLiteral
 }

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

@@ -1,6 +1,6 @@
 package gay.pizza.pork.ast
 
-class Define(val symbol: Symbol, val value: Expression) : Expression {
+class Define(val symbol: Symbol, val value: Expression) : Expression() {
   override val type: NodeType = NodeType.Define
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =

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

@@ -1,3 +1,3 @@
 package gay.pizza.pork.ast
 
-interface Expression : Node
+abstract class Expression : Node()

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

@@ -1,6 +1,6 @@
 package gay.pizza.pork.ast
 
-class FunctionCall(val symbol: Symbol, val arguments: List<Expression>) : Expression {
+class FunctionCall(val symbol: Symbol, val arguments: List<Expression>) : Expression() {
   override val type: NodeType = NodeType.FunctionCall
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =

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

@@ -4,6 +4,6 @@ class If(
   val condition: Expression,
   val thenExpression: Expression,
   val elseExpression: Expression? = null
-) : Expression {
+) : Expression() {
   override val type: NodeType = NodeType.If
 }

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

@@ -1,6 +1,6 @@
 package gay.pizza.pork.ast
 
-class InfixOperation(val left: Expression, val op: InfixOperator, val right: Expression) : Expression {
+class InfixOperation(val left: Expression, val op: InfixOperator, val right: Expression) : Expression() {
   override val type: NodeType = NodeType.InfixOperation
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =

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

@@ -1,5 +1,5 @@
 package gay.pizza.pork.ast
 
-class IntLiteral(val value: Int) : Expression {
+class IntLiteral(val value: Int) : Expression() {
   override val type: NodeType = NodeType.IntLiteral
 }

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

@@ -1,6 +1,6 @@
 package gay.pizza.pork.ast
 
-class Lambda(val arguments: List<Symbol>, val expressions: List<Expression>) : Expression {
+class Lambda(val arguments: List<Symbol>, val expressions: List<Expression>) : Expression() {
   override val type: NodeType = NodeType.Lambda
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =

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

@@ -1,6 +1,6 @@
 package gay.pizza.pork.ast
 
-class ListLiteral(val items: List<Expression>) : Expression {
+class ListLiteral(val items: List<Expression>) : Expression() {
   override val type: NodeType = NodeType.ListLiteral
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =

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

@@ -1,6 +1,8 @@
 package gay.pizza.pork.ast
 
-interface Node {
-  val type: NodeType
-  fun <T> visitChildren(visitor: Visitor<T>): List<T> = emptyList()
+abstract class Node {
+  abstract val type: NodeType
+  open fun <T> visitChildren(visitor: Visitor<T>): List<T> = emptyList()
+
+  override fun toString(): String = let { node -> buildString { Printer(this).visit(node) } }
 }

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

@@ -1,6 +1,6 @@
 package gay.pizza.pork.ast
 
-class Parentheses(val expression: Expression) : Expression {
+class Parentheses(val expression: Expression) : Expression() {
   override val type: NodeType = NodeType.Parentheses
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =

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

@@ -1,6 +1,6 @@
 package gay.pizza.pork.ast
 
-class Program(val expressions: List<Expression>) : Node {
+class Program(val expressions: List<Expression>) : Node() {
   override val type: NodeType = NodeType.Program
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =

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

@@ -1,5 +1,5 @@
 package gay.pizza.pork.ast
 
-class Symbol(val id: String) : Node {
+class Symbol(val id: String) : Node() {
   override val type: NodeType = NodeType.Symbol
 }

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

@@ -1,6 +1,6 @@
 package gay.pizza.pork.ast
 
-class SymbolReference(val symbol: Symbol) : Expression {
+class SymbolReference(val symbol: Symbol) : Expression() {
   override val type: NodeType = NodeType.SymbolReference
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =

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

@@ -109,18 +109,12 @@ class PorkParser(val source: PeekableSource<Token>) {
       }
     }
 
-    if (peekType(TokenType.Plus, TokenType.Minus, TokenType.Multiply, TokenType.Divide)) {
+    if (peekType(TokenType.Plus, TokenType.Minus, TokenType.Multiply, TokenType.Divide, TokenType.Equality)) {
       val infixToken = source.next()
       val infixOperator = convertInfixOperator(infixToken)
       return InfixOperation(expression, infixOperator, readExpression())
     }
 
-    if (peekType(TokenType.Equals)) {
-      val twoWideInfix = source.next()
-      val secondToken = expect(twoWideInfix.type)
-      return InfixOperation(expression, convertWideInfixOperator(twoWideInfix, secondToken), readExpression())
-    }
-
     return expression
   }
 
@@ -130,12 +124,7 @@ class PorkParser(val source: PeekableSource<Token>) {
       TokenType.Minus -> InfixOperator.Minus
       TokenType.Multiply -> InfixOperator.Multiply
       TokenType.Divide -> InfixOperator.Divide
-      else -> throw RuntimeException("Unknown Infix Operator")
-    }
-
-  private fun convertWideInfixOperator(firstToken: Token, secondToken: Token): InfixOperator =
-    when (firstToken.type to secondToken.type) {
-      TokenType.Equals to TokenType.Equals -> InfixOperator.Equals
+      TokenType.Equality -> InfixOperator.Equals
       else -> throw RuntimeException("Unknown Infix Operator")
     }
 

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

@@ -54,10 +54,23 @@ class PorkTokenizer(val source: CharSource, val preserveWhitespace: Boolean = fa
     while (source.peek() != CharSource.NullChar) {
       tokenStart = source.currentIndex
       val char = source.next()
+
       for (item in TokenType.SingleChars) {
-        if (item.char == char) {
-          return Token(item, char.toString())
+        if (item.char != char) {
+          continue
         }
+
+        var type = item
+        var text = item.char.toString()
+        for (promotion in item.promotions) {
+          if (source.peek() != promotion.nextChar) {
+            continue
+          }
+          val nextChar = source.next()
+          type = promotion.type
+          text += nextChar
+        }
+        return Token(type, text)
       }
 
       if (isWhitespace(char)) {

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

@@ -0,0 +1,3 @@
+package gay.pizza.pork.parse
+
+class TokenPromotion(val nextChar: Char, val type: TokenType)

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

@@ -1,9 +1,10 @@
 package gay.pizza.pork.parse
 
-enum class TokenType(val char: Char? = null, val keyword: String? = null) {
+enum class TokenType(val char: Char? = null, val keyword: String? = null, val promotions: List<TokenPromotion> = emptyList()) {
   Symbol,
   IntLiteral,
-  Equals(char = '='),
+  Equality,
+  Equals(char = '=', promotions = listOf(TokenPromotion('=', Equality))),
   Plus(char = '+'),
   Minus(char = '-'),
   Multiply(char = '*'),