diff --git a/examples/fib.pork b/examples/fib.pork
new file mode 100644
index 0000000..5d71a9a
--- /dev/null
+++ b/examples/fib.pork
@@ -0,0 +1,8 @@
+fib = { n in
+  if n == 0
+    then 0
+  else if n == 1
+    then 1
+  else fib(n - 1) + fib(n - 2)
+}
+main = { in fib(20) }
diff --git a/examples/syntax.pork b/examples/syntax.pork
index a33cc40..17a264c 100644
--- a/examples/syntax.pork
+++ b/examples/syntax.pork
@@ -1,14 +1,18 @@
-main = {
+main = { in
   three = 3
   two = 2
-  calculateSimple = {
+  calculateSimple = { in
     (50 + three) * two
   }
-  calculateComplex = {
+  calculateComplex = { in
     three + two + 50
   }
+  multiply = { a, b in
+    a * b
+  }
   calculateSimpleResult = calculateSimple()
   calculateComplexResult = calculateComplex()
+  multiplyResult = multiply(50, 50)
 
   list = [10, 20, 30]
   trueValue = true
@@ -17,6 +21,7 @@ main = {
   [
     calculateSimpleResult,
     calculateComplexResult,
+    multiplyResult,
     list,
     trueValue,
     falseValue
diff --git a/src/main/kotlin/gay/pizza/pork/ast/Define.kt b/src/main/kotlin/gay/pizza/pork/ast/Define.kt
index 44a4109..0975e68 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/Define.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/Define.kt
@@ -4,5 +4,5 @@ class Define(val symbol: Symbol, val value: Expression) : Expression {
   override val type: NodeType = NodeType.Define
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    listOf(visitor.visit(symbol), visitor.visit(value))
+    visitor.visitNodes(symbol, value)
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/FunctionCall.kt b/src/main/kotlin/gay/pizza/pork/ast/FunctionCall.kt
index a2c699e..a2f0b90 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/FunctionCall.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/FunctionCall.kt
@@ -1,8 +1,8 @@
 package gay.pizza.pork.ast
 
-class FunctionCall(val symbol: Symbol) : 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> =
-    listOf(visitor.visit(symbol))
+    visitor.visitAll(listOf(symbol), arguments)
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/If.kt b/src/main/kotlin/gay/pizza/pork/ast/If.kt
new file mode 100644
index 0000000..3ecaf27
--- /dev/null
+++ b/src/main/kotlin/gay/pizza/pork/ast/If.kt
@@ -0,0 +1,9 @@
+package gay.pizza.pork.ast
+
+class If(
+  val condition: Expression,
+  val thenExpression: Expression,
+  val elseExpression: Expression
+) : Expression {
+  override val type: NodeType = NodeType.If
+}
diff --git a/src/main/kotlin/gay/pizza/pork/ast/InfixOperation.kt b/src/main/kotlin/gay/pizza/pork/ast/InfixOperation.kt
index dc07ce4..d35f05a 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/InfixOperation.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/InfixOperation.kt
@@ -4,5 +4,5 @@ class InfixOperation(val left: Expression, val op: InfixOperator, val right: Exp
   override val type: NodeType = NodeType.InfixOperation
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    listOf(visitor.visit(left), visitor.visit(right))
+    visitor.visitNodes(left, right)
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/InfixOperator.kt b/src/main/kotlin/gay/pizza/pork/ast/InfixOperator.kt
index b2637ac..0d015c2 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/InfixOperator.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/InfixOperator.kt
@@ -4,5 +4,6 @@ enum class InfixOperator(val token: String) {
   Plus("+"),
   Minus("-"),
   Multiply("*"),
-  Divide("/")
+  Divide("/"),
+  Equals("==")
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/Lambda.kt b/src/main/kotlin/gay/pizza/pork/ast/Lambda.kt
index 653c8c0..aa0be45 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/Lambda.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/Lambda.kt
@@ -1,10 +1,8 @@
 package gay.pizza.pork.ast
 
-class Lambda(val expressions: List<Expression>) : Expression {
-  constructor(vararg expressions: Expression) : this(listOf(*expressions))
-
+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> =
-    expressions.map { expression ->  visitor.visit(expression) }
+    visitor.visitAll(arguments, expressions)
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/ListLiteral.kt b/src/main/kotlin/gay/pizza/pork/ast/ListLiteral.kt
index 0041afd..b8c467b 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/ListLiteral.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/ListLiteral.kt
@@ -1,10 +1,8 @@
 package gay.pizza.pork.ast
 
 class ListLiteral(val items: List<Expression>) : Expression {
-  constructor(vararg items: Expression) : this(listOf(*items))
-
   override val type: NodeType = NodeType.ListLiteral
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    items.map { visitor.visit(it) }
+    visitor.visitAll(items)
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/NodeType.kt b/src/main/kotlin/gay/pizza/pork/ast/NodeType.kt
index 73b9713..ff8f282 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/NodeType.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/NodeType.kt
@@ -15,7 +15,8 @@ enum class NodeType(val parent: NodeType? = null, vararg traits: NodeTypeTrait)
   Lambda(Expression),
   InfixOperation(Expression),
   SymbolReference(Expression),
-  FunctionCall(Expression);
+  FunctionCall(Expression),
+  If(Expression);
 
   val parents: Set<NodeType>
 
diff --git a/src/main/kotlin/gay/pizza/pork/ast/Parentheses.kt b/src/main/kotlin/gay/pizza/pork/ast/Parentheses.kt
index 931ff5e..b2cf606 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/Parentheses.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/Parentheses.kt
@@ -4,5 +4,5 @@ class Parentheses(val expression: Expression) : Expression {
   override val type: NodeType = NodeType.Parentheses
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    listOf(visitor.visit(expression))
+    visitor.visitNodes(expression)
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/Printer.kt b/src/main/kotlin/gay/pizza/pork/ast/Printer.kt
index 6778996..ffe96a4 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/Printer.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/Printer.kt
@@ -25,19 +25,46 @@ class Printer(private val buffer: StringBuilder) : Visitor<Unit> {
 
   override fun visitFunctionCall(node: FunctionCall) {
     visit(node.symbol)
-    append("()")
+    append("(")
+    for ((index, argument) in node.arguments.withIndex()) {
+      visit(argument)
+      if (index + 1 != node.arguments.size) {
+        append(", ")
+      }
+    }
+    append(")")
   }
 
   override fun visitReference(node: SymbolReference) {
     visit(node.symbol)
   }
 
+  override fun visitIf(node: If) {
+    append("if ")
+    visit(node.condition)
+    append(" then ")
+    visit(node.thenExpression)
+    append(" else ")
+    visit(node.elseExpression)
+  }
+
   override fun visitSymbol(node: Symbol) {
     append(node.id)
   }
 
   override fun visitLambda(node: Lambda) {
     append("{")
+    if (node.arguments.isNotEmpty()) {
+      append(" ")
+      for ((index, argument) in node.arguments.withIndex()) {
+        visit(argument)
+        if (index + 1 != node.arguments.size) {
+          append(",")
+        }
+        append(" ")
+      }
+    }
+    append("in")
     indent++
     for (expression in node.expressions) {
       appendLine()
diff --git a/src/main/kotlin/gay/pizza/pork/ast/Program.kt b/src/main/kotlin/gay/pizza/pork/ast/Program.kt
index 6eca752..5045708 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/Program.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/Program.kt
@@ -1,10 +1,8 @@
 package gay.pizza.pork.ast
 
 class Program(val expressions: List<Expression>) : Node {
-  constructor(vararg expressions: Expression) : this(listOf(*expressions))
-
   override val type: NodeType = NodeType.Program
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    expressions.map { visitor.visit(it) }
+    visitor.visitAll(expressions)
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/SymbolReference.kt b/src/main/kotlin/gay/pizza/pork/ast/SymbolReference.kt
index 2839570..714ad5e 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/SymbolReference.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/SymbolReference.kt
@@ -4,5 +4,5 @@ class SymbolReference(val symbol: Symbol) : Expression {
   override val type: NodeType = NodeType.SymbolReference
 
   override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    listOf(visitor.visit(symbol))
+    visitor.visitNodes(symbol)
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/Visitor.kt b/src/main/kotlin/gay/pizza/pork/ast/Visitor.kt
index 22cbcee..d2e166f 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/Visitor.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/Visitor.kt
@@ -4,6 +4,7 @@ interface Visitor<T> {
   fun visitDefine(node: Define): T
   fun visitFunctionCall(node: FunctionCall): T
   fun visitReference(node: SymbolReference): T
+  fun visitIf(node: If): T
   fun visitSymbol(node: Symbol): T
   fun visitLambda(node: Lambda): T
 
@@ -26,6 +27,7 @@ interface Visitor<T> {
     is Lambda -> visitLambda(node)
     is FunctionCall -> visitFunctionCall(node)
     is SymbolReference -> visitReference(node)
+    is If -> visitIf(node)
     else -> throw RuntimeException("Unknown Expression")
   }
 
@@ -35,4 +37,10 @@ interface Visitor<T> {
     is Program -> visitProgram(node)
     else -> throw RuntimeException("Unknown Node")
   }
+
+  fun visitNodes(vararg nodes: Node): List<T> =
+    nodes.map { visit(it) }
+
+  fun visitAll(vararg nodeLists: List<Node>): List<T> =
+    nodeLists.asSequence().flatten().map { visit(it) }.toList()
 }
diff --git a/src/main/kotlin/gay/pizza/pork/eval/Arguments.kt b/src/main/kotlin/gay/pizza/pork/eval/Arguments.kt
new file mode 100644
index 0000000..b9cc82c
--- /dev/null
+++ b/src/main/kotlin/gay/pizza/pork/eval/Arguments.kt
@@ -0,0 +1,7 @@
+package gay.pizza.pork.eval
+
+class Arguments(val values: List<Any>) {
+  companion object {
+    val Zero = Arguments(emptyList())
+  }
+}
diff --git a/src/main/kotlin/gay/pizza/pork/eval/CallableFunction.kt b/src/main/kotlin/gay/pizza/pork/eval/CallableFunction.kt
index 7b310fd..d06ef7b 100644
--- a/src/main/kotlin/gay/pizza/pork/eval/CallableFunction.kt
+++ b/src/main/kotlin/gay/pizza/pork/eval/CallableFunction.kt
@@ -1,5 +1,5 @@
 package gay.pizza.pork.eval
 
 fun interface CallableFunction {
-  fun call(argument: Any): Any
+  fun call(arguments: Arguments): Any
 }
diff --git a/src/main/kotlin/gay/pizza/pork/eval/PorkEvaluator.kt b/src/main/kotlin/gay/pizza/pork/eval/PorkEvaluator.kt
index fcedcd1..00c9893 100644
--- a/src/main/kotlin/gay/pizza/pork/eval/PorkEvaluator.kt
+++ b/src/main/kotlin/gay/pizza/pork/eval/PorkEvaluator.kt
@@ -11,18 +11,33 @@ class PorkEvaluator(root: Scope) : Visitor<Any> {
     return value
   }
 
-  override fun visitFunctionCall(node: FunctionCall): Any = currentScope.call(node.symbol.id)
+  override fun visitFunctionCall(node: FunctionCall): Any {
+    val arguments = node.arguments.map { visit(it) }
+    return currentScope.call(node.symbol.id, Arguments(arguments))
+  }
 
   override fun visitReference(node: SymbolReference): Any =
     currentScope.value(node.symbol.id)
 
+  override fun visitIf(node: If): Any {
+    val condition = visit(node.condition)
+    return if (condition == true) {
+      visit(node.thenExpression)
+    } else {
+      visit(node.elseExpression)
+    }
+  }
+
   override fun visitSymbol(node: Symbol): Any {
     return Unit
   }
 
   override fun visitLambda(node: Lambda): CallableFunction {
-    return CallableFunction { _ ->
+    return CallableFunction { arguments ->
       currentScope = currentScope.fork()
+      for ((index, argumentSymbol) in node.arguments.withIndex()) {
+        currentScope.define(argumentSymbol.id, arguments.values[index])
+      }
       try {
         var value: Any? = null
         for (expression in node.expressions) {
@@ -45,6 +60,13 @@ class PorkEvaluator(root: Scope) : Visitor<Any> {
     val left = visit(node.left)
     val right = visit(node.right)
 
+    when (node.op) {
+      InfixOperator.Equals -> {
+        return left == right
+      }
+      else -> {}
+    }
+
     if (left !is Number || right !is Number) {
       throw RuntimeException("Failed to evaluate infix operation, bad types.")
     }
@@ -57,6 +79,7 @@ class PorkEvaluator(root: Scope) : Visitor<Any> {
       InfixOperator.Minus -> leftInt - rightInt
       InfixOperator.Multiply -> leftInt * rightInt
       InfixOperator.Divide -> leftInt / rightInt
+      else -> throw RuntimeException("Unable to handle operation ${node.op}")
     }
   }
 
diff --git a/src/main/kotlin/gay/pizza/pork/eval/Scope.kt b/src/main/kotlin/gay/pizza/pork/eval/Scope.kt
index dcaf64b..78e7a6a 100644
--- a/src/main/kotlin/gay/pizza/pork/eval/Scope.kt
+++ b/src/main/kotlin/gay/pizza/pork/eval/Scope.kt
@@ -21,13 +21,12 @@ class Scope(val parent: Scope? = null) {
     return value
   }
 
-  fun call(name: String, argument: Any = Unit): Any {
+  fun call(name: String, arguments: Arguments): Any {
     val value = value(name)
     if (value !is CallableFunction) {
       throw RuntimeException("$value is not callable.")
     }
-    val function = value as CallableFunction
-    return function.call(argument)
+    return value.call(arguments)
   }
 
   fun fork(): Scope {
diff --git a/src/main/kotlin/gay/pizza/pork/main.kt b/src/main/kotlin/gay/pizza/pork/main.kt
index fbdc4ac..fa93067 100644
--- a/src/main/kotlin/gay/pizza/pork/main.kt
+++ b/src/main/kotlin/gay/pizza/pork/main.kt
@@ -1,6 +1,7 @@
 package gay.pizza.pork
 
 import gay.pizza.pork.ast.*
+import gay.pizza.pork.eval.Arguments
 import gay.pizza.pork.eval.Scope
 import gay.pizza.pork.eval.PorkEvaluator
 import gay.pizza.pork.parse.*
@@ -12,7 +13,7 @@ fun main(args: Array<String>) {
     val scope = Scope()
     val evaluator = PorkEvaluator(scope)
     evaluator.visit(ast)
-    println("> ${scope.call("main")}")
+    println("> ${scope.call("main", Arguments.Zero)}")
   }
 
   val code = Path(args[0]).readText()
diff --git a/src/main/kotlin/gay/pizza/pork/parse/PeekableSource.kt b/src/main/kotlin/gay/pizza/pork/parse/PeekableSource.kt
index 6335c4c..c8c2ece 100644
--- a/src/main/kotlin/gay/pizza/pork/parse/PeekableSource.kt
+++ b/src/main/kotlin/gay/pizza/pork/parse/PeekableSource.kt
@@ -2,6 +2,7 @@ package gay.pizza.pork.parse
 
 interface PeekableSource<T> {
   val currentIndex: Int
+  fun back()
   fun next(): T
   fun peek(): T
 }
diff --git a/src/main/kotlin/gay/pizza/pork/parse/PorkParser.kt b/src/main/kotlin/gay/pizza/pork/parse/PorkParser.kt
index a52ac99..c90b0d9 100644
--- a/src/main/kotlin/gay/pizza/pork/parse/PorkParser.kt
+++ b/src/main/kotlin/gay/pizza/pork/parse/PorkParser.kt
@@ -13,14 +13,29 @@ class PorkParser(val source: PeekableSource<Token>) {
     return Symbol(token.text)
   }
 
+  private fun readIf(): If {
+    expect(TokenType.If)
+    val condition = readExpression()
+    expect(TokenType.Then)
+    val thenExpression = readExpression()
+    expect(TokenType.Else)
+    val elseExpression = readExpression()
+    return If(condition, thenExpression, elseExpression)
+  }
+
   private fun readSymbolCases(): Expression {
     val symbol = readSymbol()
     return if (peekType(TokenType.LeftParentheses)) {
       expect(TokenType.LeftParentheses)
+      val arguments = collectExpressions(TokenType.RightParentheses, TokenType.Comma)
       expect(TokenType.RightParentheses)
-      FunctionCall(symbol)
+      FunctionCall(symbol, arguments)
     } else if (peekType(TokenType.Equals)) {
       expect(TokenType.Equals)
+      if (peekType(TokenType.Equals)) {
+        source.back()
+        return SymbolReference(symbol)
+      }
       Define(symbol, readExpression())
     } else {
       SymbolReference(symbol)
@@ -29,9 +44,21 @@ class PorkParser(val source: PeekableSource<Token>) {
 
   fun readLambda(): Lambda {
     expect(TokenType.LeftCurly)
+    val arguments = mutableListOf<Symbol>()
+    while (!peekType(TokenType.In)) {
+      val symbol = readSymbol()
+      arguments.add(symbol)
+      if (peekType(TokenType.Comma)) {
+        expect(TokenType.Comma)
+        continue
+      } else {
+        break
+      }
+    }
+    expect(TokenType.In)
     val items = collectExpressions(TokenType.RightCurly)
     expect(TokenType.RightCurly)
-    return Lambda(items)
+    return Lambda(arguments, items)
   }
 
   fun readExpression(): Expression {
@@ -40,31 +67,42 @@ class PorkParser(val source: PeekableSource<Token>) {
       TokenType.IntLiteral -> {
         readIntLiteral()
       }
+
       TokenType.LeftBracket -> {
         readListLiteral()
       }
+
       TokenType.Symbol -> {
         readSymbolCases()
       }
+
       TokenType.LeftCurly -> {
         readLambda()
       }
+
       TokenType.LeftParentheses -> {
         expect(TokenType.LeftParentheses)
         val expression = readExpression()
         expect(TokenType.RightParentheses)
         Parentheses(expression)
       }
+
       TokenType.True -> {
         expect(TokenType.True)
         return BooleanLiteral(true)
       }
+
       TokenType.False -> {
         expect(TokenType.False)
         return BooleanLiteral(false)
       }
+
+      TokenType.If -> {
+        return readIf()
+      }
+
       else -> {
-        throw RuntimeException("Failed to parse token: ${token.type} '${token.text}' as expression.")
+        throw RuntimeException("Failed to parse token: ${token.type} '${token.text}' as expression")
       }
     }
 
@@ -73,6 +111,13 @@ class PorkParser(val source: PeekableSource<Token>) {
       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
   }
 
@@ -85,6 +130,12 @@ class PorkParser(val source: PeekableSource<Token>) {
       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
+      else -> throw RuntimeException("Unknown Infix Operator")
+    }
+
   fun readListLiteral(): ListLiteral {
     expect(TokenType.LeftBracket)
     val items = collectExpressions(TokenType.RightBracket, TokenType.Comma)
diff --git a/src/main/kotlin/gay/pizza/pork/parse/StringCharSource.kt b/src/main/kotlin/gay/pizza/pork/parse/StringCharSource.kt
index 6d7d996..540c57d 100644
--- a/src/main/kotlin/gay/pizza/pork/parse/StringCharSource.kt
+++ b/src/main/kotlin/gay/pizza/pork/parse/StringCharSource.kt
@@ -3,6 +3,9 @@ package gay.pizza.pork.parse
 class StringCharSource(val input: String) : CharSource {
   private var index = 0
   override val currentIndex: Int = index
+  override fun back() {
+    index--
+  }
 
   override fun next(): Char {
     if (index == input.length) {
diff --git a/src/main/kotlin/gay/pizza/pork/parse/TokenStreamSource.kt b/src/main/kotlin/gay/pizza/pork/parse/TokenStreamSource.kt
index 3719415..b2ea3a7 100644
--- a/src/main/kotlin/gay/pizza/pork/parse/TokenStreamSource.kt
+++ b/src/main/kotlin/gay/pizza/pork/parse/TokenStreamSource.kt
@@ -3,6 +3,9 @@ package gay.pizza.pork.parse
 class TokenStreamSource(val stream: TokenStream) : TokenSource {
   private var index = 0
   override val currentIndex: Int = index
+  override fun back() {
+    index--
+  }
 
   override fun next(): Token {
     if (index == stream.tokens.size) {
diff --git a/src/main/kotlin/gay/pizza/pork/parse/TokenType.kt b/src/main/kotlin/gay/pizza/pork/parse/TokenType.kt
index d586677..83d7c75 100644
--- a/src/main/kotlin/gay/pizza/pork/parse/TokenType.kt
+++ b/src/main/kotlin/gay/pizza/pork/parse/TokenType.kt
@@ -18,6 +18,9 @@ enum class TokenType(val char: Char? = null, val keyword: String? = null) {
   False(keyword = "false"),
   True(keyword = "true"),
   In(keyword = "in"),
+  If(keyword = "if"),
+  Then(keyword = "then"),
+  Else(keyword = "else"),
   EndOfFile;
 
   companion object {