diff --git a/src/main/kotlin/gay/pizza/pork/ast/NodeVisitor.kt b/src/main/kotlin/gay/pizza/pork/ast/NodeVisitor.kt
index a2e9cfb..71f3bde 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/NodeVisitor.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/NodeVisitor.kt
@@ -42,8 +42,8 @@ interface NodeVisitor<T> {
     else -> throw RuntimeException("Unknown Node")
   }
 
-  fun visitNodes(vararg nodes: Node): List<T> =
-    nodes.map { visit(it) }
+  fun visitNodes(vararg nodes: Node?): List<T> =
+    nodes.filterNotNull().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/ast/nodes/BooleanLiteral.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/BooleanLiteral.kt
index 28d95b9..f2368d8 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/BooleanLiteral.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/BooleanLiteral.kt
@@ -4,4 +4,15 @@ import gay.pizza.pork.ast.NodeType
 
 class BooleanLiteral(val value: Boolean) : Expression() {
   override val type: NodeType = NodeType.BooleanLiteral
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is BooleanLiteral) return false
+    return other.value == value
+  }
+
+  override fun hashCode(): Int {
+    var result = value.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/Define.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/Define.kt
index 0b0bb5d..adc8d2d 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/Define.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/Define.kt
@@ -8,4 +8,16 @@ class Define(val symbol: Symbol, val value: Expression) : Expression() {
 
   override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitNodes(symbol, value)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is Define) return false
+    return other.symbol == symbol && other.value == value
+  }
+
+  override fun hashCode(): Int {
+    var result = symbol.hashCode()
+    result = 31 * result + value.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/FunctionCall.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/FunctionCall.kt
index 67ad888..12b23b3 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/FunctionCall.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/FunctionCall.kt
@@ -8,4 +8,9 @@ class FunctionCall(val symbol: Symbol, val arguments: List<Expression>) : Expres
 
   override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitAll(listOf(symbol), arguments)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is FunctionCall) return false
+    return other.symbol == symbol && other.arguments == arguments
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/If.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/If.kt
index 39ccbe7..aed20ee 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/If.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/If.kt
@@ -1,6 +1,7 @@
 package gay.pizza.pork.ast.nodes
 
 import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
 
 class If(
   val condition: Expression,
@@ -8,4 +9,22 @@ class If(
   val elseExpression: Expression? = null
 ) : Expression() {
   override val type: NodeType = NodeType.If
+
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
+    visitor.visitNodes(condition, thenExpression, elseExpression)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is If) return false
+    return other.condition == condition &&
+      other.thenExpression == thenExpression &&
+      other.elseExpression == elseExpression
+  }
+
+  override fun hashCode(): Int {
+    var result = condition.hashCode()
+    result = 31 * result + thenExpression.hashCode()
+    result = 31 * result + (elseExpression?.hashCode() ?: 0)
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/InfixOperation.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/InfixOperation.kt
index e863664..043d3bb 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/InfixOperation.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/InfixOperation.kt
@@ -3,9 +3,28 @@ package gay.pizza.pork.ast.nodes
 import gay.pizza.pork.ast.NodeType
 import gay.pizza.pork.ast.NodeVisitor
 
-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: NodeVisitor<T>): List<T> =
     visitor.visitNodes(left, right)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is InfixOperation) return false
+    return other.op == op &&
+      other.left == left &&
+      other.right == right
+  }
+
+  override fun hashCode(): Int {
+    var result = left.hashCode()
+    result = 31 * result + op.hashCode()
+    result = 31 * result + right.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/IntLiteral.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/IntLiteral.kt
index af2e034..4966b39 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/IntLiteral.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/IntLiteral.kt
@@ -4,4 +4,15 @@ import gay.pizza.pork.ast.NodeType
 
 class IntLiteral(val value: Int) : Expression() {
   override val type: NodeType = NodeType.IntLiteral
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is IntLiteral) return false
+    return other.value == value
+  }
+
+  override fun hashCode(): Int {
+    var result = value
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/Lambda.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/Lambda.kt
index 0b92492..156de36 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/Lambda.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/Lambda.kt
@@ -8,4 +8,16 @@ class Lambda(val arguments: List<Symbol>, val expressions: List<Expression>) : E
 
   override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitAll(arguments, expressions)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is Lambda) return false
+    return other.arguments == arguments && other.expressions == expressions
+  }
+
+  override fun hashCode(): Int {
+    var result = arguments.hashCode()
+    result = 31 * result + expressions.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/ListLiteral.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/ListLiteral.kt
index 2685e99..64a2b1a 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/ListLiteral.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/ListLiteral.kt
@@ -8,4 +8,15 @@ class ListLiteral(val items: List<Expression>) : Expression() {
 
   override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitAll(items)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is ListLiteral) return false
+    return other.items == items
+  }
+
+  override fun hashCode(): Int {
+    var result = items.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/Parentheses.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/Parentheses.kt
index 9bb8e6c..b7be5fc 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/Parentheses.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/Parentheses.kt
@@ -8,4 +8,15 @@ class Parentheses(val expression: Expression) : Expression() {
 
   override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitNodes(expression)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is Parentheses) return false
+    return other.expression == expression
+  }
+
+  override fun hashCode(): Int {
+    var result = expression.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/PrefixOperation.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/PrefixOperation.kt
index 24c0b3a..dd00638 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/PrefixOperation.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/PrefixOperation.kt
@@ -1,7 +1,23 @@
 package gay.pizza.pork.ast.nodes
 
 import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
 
 class PrefixOperation(val op: PrefixOperator, val expression: Expression) : Expression() {
   override val type: NodeType = NodeType.PrefixOperation
+
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
+    visitor.visitNodes(expression)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is PrefixOperation) return false
+    return other.op == op && other.expression == expression
+  }
+
+  override fun hashCode(): Int {
+    var result = op.hashCode()
+    result = 31 * result + expression.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/Program.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/Program.kt
index 1871444..586b922 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/Program.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/Program.kt
@@ -8,4 +8,15 @@ class Program(val expressions: List<Expression>) : Node() {
 
   override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitAll(expressions)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is Program) return false
+    return other.expressions == expressions
+  }
+
+  override fun hashCode(): Int {
+    var result = expressions.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/Symbol.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/Symbol.kt
index 1cad7ae..6efaf42 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/Symbol.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/Symbol.kt
@@ -4,4 +4,15 @@ import gay.pizza.pork.ast.NodeType
 
 class Symbol(val id: String) : Node() {
   override val type: NodeType = NodeType.Symbol
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is Symbol) return false
+    return other.id == id
+  }
+
+  override fun hashCode(): Int {
+    var result = id.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }
diff --git a/src/main/kotlin/gay/pizza/pork/ast/nodes/SymbolReference.kt b/src/main/kotlin/gay/pizza/pork/ast/nodes/SymbolReference.kt
index 78816d2..3156376 100644
--- a/src/main/kotlin/gay/pizza/pork/ast/nodes/SymbolReference.kt
+++ b/src/main/kotlin/gay/pizza/pork/ast/nodes/SymbolReference.kt
@@ -8,4 +8,15 @@ class SymbolReference(val symbol: Symbol) : Expression() {
 
   override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitNodes(symbol)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is SymbolReference) return false
+    return other.symbol == symbol
+  }
+
+  override fun hashCode(): Int {
+    var result = symbol.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
 }