Declaration based compilation units.

README.md

@@ -6,7 +6,7 @@ Very WIP. Like VERY.
 
 ```pork
 /* fibonacci sequence */
-fib = { n in
+fn fib(n) {
   if n == 0
     then 0
   else if n == 1
@@ -14,8 +14,10 @@ fib = { n in
   else fib(n - 1) + fib(n - 2)
 }
 
-result = fib(20)
-println(result)
+fn main() {
+  result = fib(20)
+  println(result)
+}
 ```
 
 ## Usage

examples/commented.pork

@@ -1,17 +0,0 @@
-/* fibonacci sequence */
-/**
- * fib(n): calculate the fibonacci sequence.
- * @input n the number to calculate fibonacci for
- * @result the value of the fibonacci sequence for the number
- */
-fib = { n in
-  if n == 0 // if n is zero, return zero
-    then 0
-  else if n == 1 // if n is one, return one
-    then 1
-  else fib(n - 1) + fib(n - 2)
-}
-
-// result of fib(20)
-result = fib(20)
-println(result)

examples/fib.pork

@@ -1,5 +1,5 @@
 /* fibonacci sequence */
-fib = { n in
+fn fib(n) {
   if n == 0
     then 0
   else if n == 1
@@ -7,5 +7,7 @@ fib = { n in
   else fib(n - 1) + fib(n - 2)
 }
 
-result = fib(20)
-println(result)
+fn main() {
+  result = fib(20)
+  println(result)
+}

examples/syntax.pork

@@ -1,53 +1,55 @@
-three = 3
-two = 2
+fn main() {
+  three = 3
+  two = 2
 
-calculateSimple = { in
-  (50 + three) * two
+  calculateSimple = { in
+    (50 + three) * two
+  }
+
+  calculateComplex = { in
+    three + two + 50
+  }
+
+  multiply = { a, b in
+    a * b
+  }
+
+  // calculates the result
+  calculateSimpleResult = calculateSimple()
+  calculateComplexResult = calculateComplex()
+  multiplyResult = multiply(50, 50)
+
+  list = [10, 20, 30]
+  trueValue = true
+  falseValue = false
+
+  invert = { value in
+    !value
+  }
+
+  notEqual = { a, b in
+    a != b
+  }
+
+  equal = { a, b in
+    a == b
+  }
+
+  results = [
+    calculateSimpleResult,
+    calculateComplexResult,
+    multiplyResult,
+    list,
+    trueValue,
+    falseValue,
+    invert(true),
+    invert(false),
+    equal(5, 5),
+    equal(5, 6),
+    notEqual(5, 5),
+    notEqual(5, 6)
+  ]
+
+  println("results:")
+  println(results)
 }
-
-calculateComplex = { in
-  three + two + 50
-}
-
-multiply = { a, b in
-  a * b
-}
-
-// calculates the result
-calculateSimpleResult = calculateSimple()
-calculateComplexResult = calculateComplex()
-multiplyResult = multiply(50, 50)
-
-list = [10, 20, 30]
-trueValue = true
-falseValue = false
-
-invert = { value in
-  !value
-}
-
-notEqual = { a, b in
-  a != b
-}
-
-equal = { a, b in
-  a == b
-}
-
-results = [
-  calculateSimpleResult,
-  calculateComplexResult,
-  multiplyResult,
-  list,
-  trueValue,
-  falseValue,
-  invert(true),
-  invert(false),
-  equal(5, 5),
-  equal(5, 6),
-  notEqual(5, 5),
-  notEqual(5, 6)
-]
-
-println("results:")
-println(results)

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

@@ -16,7 +16,10 @@ class NodeCoalescer(val handler: (Node) -> Unit) : NodeVisitor<Unit> {
   override fun visitPrefixOperation(node: PrefixOperation): Unit = handle(node)
   override fun visitIf(node: If): Unit = handle(node)
   override fun visitInfixOperation(node: InfixOperation): Unit = handle(node)
-  override fun visitProgram(node: Program): Unit = handle(node)
+  override fun visitFunctionDeclaration(node: FunctionDeclaration): Unit = handle(node)
+  override fun visitBlock(node: Block): Unit = handle(node)
+
+  override fun visitCompilationUnit(node: CompilationUnit): Unit = handle(node)
 
   private fun handle(node: Node) {
     handler(node)

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

@@ -4,7 +4,9 @@ enum class NodeType(val parent: NodeType? = null) {
   Node,
   Symbol(Node),
   Expression(Node),
-  Program(Node),
+  Declaration(Node),
+  Block(Node),
+  CompilationUnit(Node),
   IntLiteral(Expression),
   BooleanLiteral(Expression),
   ListLiteral(Expression),
@@ -16,7 +18,8 @@ enum class NodeType(val parent: NodeType? = null) {
   InfixOperation(Expression),
   SymbolReference(Expression),
   FunctionCall(Expression),
-  If(Expression);
+  If(Expression),
+  FunctionDeclaration(Declaration);
 
   val parents: Set<NodeType>
 

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

@@ -16,7 +16,10 @@ interface NodeVisitor<T> {
   fun visitPrefixOperation(node: PrefixOperation): T
   fun visitIf(node: If): T
   fun visitInfixOperation(node: InfixOperation): T
-  fun visitProgram(node: Program): T
+  fun visitFunctionDeclaration(node: FunctionDeclaration): T
+  fun visitBlock(node: Block): T
+
+  fun visitCompilationUnit(node: CompilationUnit): T
 
   fun visitExpression(node: Expression): T = when (node) {
     is IntLiteral -> visitIntLiteral(node)
@@ -33,10 +36,16 @@ interface NodeVisitor<T> {
     is InfixOperation -> visitInfixOperation(node)
   }
 
+  fun visitDeclaration(node: Declaration): T = when (node) {
+    is FunctionDeclaration -> visitFunctionDeclaration(node)
+  }
+
   fun visit(node: Node): T = when (node) {
     is Symbol -> visitSymbol(node)
     is Expression -> visitExpression(node)
-    is Program -> visitProgram(node)
+    is CompilationUnit -> visitCompilationUnit(node)
+    is Block -> visitBlock(node)
+    is Declaration -> visitDeclaration(node)
   }
 
   fun visitNodes(vararg nodes: Node?): List<T> =

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

@@ -82,7 +82,6 @@ class Printer(buffer: StringBuilder) : NodeVisitor<Unit> {
     visit(node.symbol)
   }
 
-
   override fun visitLambda(node: Lambda) {
     append("{")
     if (node.arguments.isNotEmpty()) {
@@ -148,10 +147,37 @@ class Printer(buffer: StringBuilder) : NodeVisitor<Unit> {
     visit(node.right)
   }
 
-  override fun visitProgram(node: Program) {
-    for (expression in node.expressions) {
-      out.emitIndent()
-      visit(expression)
+  override fun visitFunctionDeclaration(node: FunctionDeclaration) {
+    append("fn ")
+    visit(node.symbol)
+    append("(")
+    for ((index, argument) in node.arguments.withIndex()) {
+      visit(argument)
+      if (index + 1 != node.arguments.size) {
+        append(", ")
+      }
+    }
+    append(") ")
+    visit(node.block)
+  }
+
+  override fun visitBlock(node: Block) {
+    append("{")
+    if (node.expressions.isNotEmpty()) {
+      out.increaseIndent()
+      for (expression in node.expressions) {
+        appendLine()
+        visit(expression)
+      }
+      out.decreaseIndent()
+      appendLine()
+    }
+    append("}")
+  }
+
+  override fun visitCompilationUnit(node: CompilationUnit) {
+    for (declaration in node.declarations) {
+      visit(declaration)
       appendLine()
     }
   }

src/main/kotlin/gay/pizza/pork/ast/nodes/Block.kt

@@ -6,15 +6,15 @@ import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 
 @Serializable
-@SerialName("program")
-class Program(val expressions: List<Expression>) : Node() {
-  override val type: NodeType = NodeType.Program
+@SerialName("block")
+class Block(val expressions: List<Expression>) : Node() {
+  override val type: NodeType = NodeType.Block
 
   override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitAll(expressions)
 
   override fun equals(other: Any?): Boolean {
-    if (other !is Program) return false
+    if (other !is Block) return false
     return other.expressions == expressions
   }
 

src/main/kotlin/gay/pizza/pork/ast/nodes/CompilationUnit.kt

@@ -0,0 +1,26 @@
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+@Serializable
+@SerialName("compilationUnit")
+class CompilationUnit(val declarations: List<Declaration>) : Node() {
+  override val type: NodeType = NodeType.CompilationUnit
+
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
+    visitor.visitAll(declarations)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is CompilationUnit) return false
+    return other.declarations == declarations
+  }
+
+  override fun hashCode(): Int {
+    var result = declarations.hashCode()
+    result = 31 * result + type.hashCode()
+    return result
+  }
+}

src/main/kotlin/gay/pizza/pork/ast/nodes/Declaration.kt

@@ -0,0 +1,6 @@
+package gay.pizza.pork.ast.nodes
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+sealed class Declaration : Node()

src/main/kotlin/gay/pizza/pork/ast/nodes/FunctionDeclaration.kt

@@ -0,0 +1,28 @@
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+@Serializable
+@SerialName("functionDeclaration")
+class FunctionDeclaration(val symbol: Symbol, val arguments: List<Symbol>, val block: Block) : Declaration() {
+  override val type: NodeType = NodeType.FunctionDeclaration
+
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
+    visitor.visitNodes(symbol)
+
+  override fun equals(other: Any?): Boolean {
+    if (other !is FunctionDeclaration) return false
+    return other.symbol == symbol && other.arguments == arguments && other.block == block
+  }
+
+  override fun hashCode(): Int {
+    var result = symbol.hashCode()
+    result = 31 * result + symbol.hashCode()
+    result = 31 * result + arguments.hashCode()
+    result = 31 * result + block.hashCode()
+    return result
+  }
+}

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

@@ -13,7 +13,7 @@ class AttributeCommand : CliktCommand(help = "Attribute AST", name = "attribute"
   override fun run() {
     val frontend = FileFrontend(path)
     val attribution = TokenNodeAttribution()
-    val program = frontend.parse(attribution)
+    val compilationUnit = frontend.parse(attribution)
 
     val coalescer = NodeCoalescer { node ->
       val tokens = attribution.assembleTokens(node)
@@ -22,6 +22,6 @@ class AttributeCommand : CliktCommand(help = "Attribute AST", name = "attribute"
         println("token $token")
       }
     }
-    coalescer.visit(program)
+    coalescer.visit(compilationUnit)
   }
 }

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

@@ -1,16 +0,0 @@
-package gay.pizza.pork.cli
-
-import com.github.ajalt.clikt.core.CliktCommand
-import com.github.ajalt.clikt.parameters.arguments.argument
-import com.github.ajalt.clikt.parameters.types.path
-import gay.pizza.pork.compiler.DartCompiler
-import gay.pizza.pork.frontend.FileFrontend
-
-class GenerateDartCommand : CliktCommand(help = "Generate Dart Code", name = "generate-dart") {
-  val path by argument("file").path(mustExist = true, canBeDir = false)
-
-  override fun run() {
-    val frontend = FileFrontend(path)
-    println(frontend.visit(DartCompiler()))
-  }
-}

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

@@ -1,16 +0,0 @@
-package gay.pizza.pork.cli
-
-import com.github.ajalt.clikt.core.CliktCommand
-import com.github.ajalt.clikt.parameters.arguments.argument
-import com.github.ajalt.clikt.parameters.types.path
-import gay.pizza.pork.compiler.KotlinCompiler
-import gay.pizza.pork.frontend.FileFrontend
-
-class GenerateKotlinCommand : CliktCommand(help = "Generate Kotlin Code", name = "generate-kotlin") {
-  val path by argument("file").path(mustExist = true, canBeDir = false)
-
-  override fun run() {
-    val frontend = FileFrontend(path)
-    println(frontend.visit(KotlinCompiler()))
-  }
-}

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

@@ -5,7 +5,7 @@ import com.github.ajalt.clikt.parameters.arguments.argument
 import com.github.ajalt.clikt.parameters.types.path
 import gay.pizza.pork.frontend.FileFrontend
 
-class ReprintCommand : CliktCommand(help = "Reprint Parsed Program", name = "reprint") {
+class ReprintCommand : CliktCommand(help = "Reprint Parsed Compilation Unit", name = "reprint") {
   val path by argument("file").path(mustExist = true, canBeDir = false)
 
   override fun run() {

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

@@ -14,9 +14,7 @@ class RootCommand : CliktCommand(
       TokenizeCommand(),
       ReprintCommand(),
       AstCommand(),
-      AttributeCommand(),
-      GenerateKotlinCommand(),
-      GenerateDartCommand()
+      AttributeCommand()
     )
   }
 

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

@@ -3,6 +3,7 @@ package gay.pizza.pork.cli
 import com.github.ajalt.clikt.core.CliktCommand
 import com.github.ajalt.clikt.parameters.arguments.argument
 import com.github.ajalt.clikt.parameters.types.path
+import gay.pizza.pork.eval.Arguments
 import gay.pizza.pork.eval.CallableFunction
 import gay.pizza.pork.eval.Scope
 import gay.pizza.pork.frontend.FileFrontend
@@ -19,5 +20,6 @@ class RunCommand : CliktCommand(help = "Run Program", name = "run") {
       }
     })
     frontend.evaluate(scope)
+    scope.call("main", Arguments(emptyList()))
   }
 }

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

@@ -5,7 +5,7 @@ import com.github.ajalt.clikt.parameters.arguments.argument
 import com.github.ajalt.clikt.parameters.types.path
 import gay.pizza.pork.frontend.FileFrontend
 
-class TokenizeCommand : CliktCommand(help = "Tokenize Program", name = "tokenize") {
+class TokenizeCommand : CliktCommand(help = "Tokenize Compilation Unit", name = "tokenize") {
   val path by argument("file").path(mustExist = true, canBeDir = false)
 
   override fun run() {

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

@@ -1,90 +0,0 @@
-package gay.pizza.pork.compiler
-
-import gay.pizza.pork.ast.NodeVisitor
-import gay.pizza.pork.ast.nodes.*
-import gay.pizza.pork.util.StringEscape
-
-class DartCompiler : NodeVisitor<String> {
-  override fun visitIntLiteral(node: IntLiteral): String =
-    node.value.toString()
-
-  override fun visitStringLiteral(node: StringLiteral): String =
-    "\"" + StringEscape.escape(node.text) + "\""
-
-  override fun visitBooleanLiteral(node: BooleanLiteral): String =
-    node.value.toString()
-
-  override fun visitListLiteral(node: ListLiteral): String = buildString {
-    append("[")
-    for ((index, item) in node.items.withIndex()) {
-      appendLine()
-      append(visit(item))
-      if (index + 1 != node.items.size) {
-        append(",")
-      }
-    }
-    append("]")
-  }
-
-  override fun visitSymbol(node: Symbol): String =
-    node.id
-
-  override fun visitFunctionCall(node: FunctionCall): String =
-    "${visit(node.symbol)}(${node.arguments.joinToString(", ") { visit(it) }})"
-
-  override fun visitDefine(node: Define): String =
-    "final ${visit(node.symbol)} = ${visit(node.value)};"
-
-  override fun visitSymbolReference(node: SymbolReference): String =
-    visit(node.symbol)
-
-  override fun visitLambda(node: Lambda): String = buildString {
-    append("(${node.arguments.joinToString(", ") { visit(it) }}) {")
-    appendLine()
-    for ((index, expression) in node.expressions.withIndex()) {
-      val code = visit(expression)
-      if (index == node.expressions.size - 1) {
-        append("return ");
-      }
-      append(code)
-      append(";")
-    }
-    appendLine()
-    append("}")
-  }
-
-  override fun visitParentheses(node: Parentheses): String =
-    "(${visit(node.expression)})"
-
-  override fun visitPrefixOperation(node: PrefixOperation): String =
-    "${node.op.token}${visit(node.expression)}"
-
-  override fun visitIf(node: If): String = buildString {
-    append("if (")
-    append(visit(node.condition))
-    append(") {")
-    append(visit(node.thenExpression))
-    append("}")
-    if (node.elseExpression != null) {
-      append(" else {")
-      append(visit(node.elseExpression))
-      append("}")
-    }
-  }
-
-  override fun visitInfixOperation(node: InfixOperation): String =
-    "${visit(node.left)} ${node.op.token} ${visit(node.right)}"
-
-  override fun visitProgram(node: Program): String = buildString {
-    appendLine("void main() {")
-    for (item in node.expressions) {
-      append(visit(item))
-      if (!endsWith(";")) {
-        append(";")
-      }
-      append(";")
-      appendLine()
-    }
-    appendLine("}")
-  }
-}

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

@@ -1,78 +0,0 @@
-package gay.pizza.pork.compiler
-
-import gay.pizza.pork.ast.*
-import gay.pizza.pork.ast.nodes.*
-import gay.pizza.pork.util.StringEscape
-
-class KotlinCompiler : NodeVisitor<String> {
-  override fun visitIntLiteral(node: IntLiteral): String =
-    node.value.toString()
-
-  override fun visitStringLiteral(node: StringLiteral): String =
-    "\"" + StringEscape.escape(node.text) + "\""
-
-  override fun visitBooleanLiteral(node: BooleanLiteral): String =
-    node.value.toString()
-
-  override fun visitListLiteral(node: ListLiteral): String = buildString {
-    append("listOf(")
-    for ((index, item) in node.items.withIndex()) {
-      appendLine()
-      append(visit(item))
-      if (index + 1 != node.items.size) {
-        append(",")
-      }
-    }
-    append(")")
-  }
-
-  override fun visitSymbol(node: Symbol): String =
-    node.id
-
-  override fun visitFunctionCall(node: FunctionCall): String =
-    "${visit(node.symbol)}(${node.arguments.joinToString(", ") { visit(it) }})"
-
-  override fun visitDefine(node: Define): String =
-    "val ${visit(node.symbol)} = ${visit(node.value)}"
-
-  override fun visitSymbolReference(node: SymbolReference): String =
-    visit(node.symbol)
-
-  override fun visitLambda(node: Lambda): String = buildString {
-    append("{ ${node.arguments.joinToString(", ") { visit(it) }} ->")
-    appendLine()
-    append(visitAll(node.expressions).joinToString("\n"))
-    appendLine()
-    append("}")
-  }
-
-  override fun visitParentheses(node: Parentheses): String =
-    "(${visit(node.expression)})"
-
-  override fun visitPrefixOperation(node: PrefixOperation): String =
-    "${node.op.token}${visit(node.expression)}"
-
-  override fun visitIf(node: If): String = buildString {
-    append("if (")
-    append(visit(node.condition))
-    append(") {")
-    append(visit(node.thenExpression))
-    append("}")
-    if (node.elseExpression != null) {
-      append(" else {")
-      append(visit(node.elseExpression))
-      append("}")
-    }
-  }
-
-  override fun visitInfixOperation(node: InfixOperation): String =
-    "${visit(node.left)} ${node.op.token} ${visit(node.right)}"
-
-  override fun visitProgram(node: Program): String = buildString {
-    appendLine("fun main() {")
-    for (item in node.expressions) {
-      appendLine(visit(item))
-    }
-    appendLine("}")
-  }
-}

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

@@ -0,0 +1,5 @@
+package gay.pizza.pork.eval
+
+fun interface BlockFunction {
+  fun call(): Any
+}

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

@@ -1,6 +1,6 @@
 package gay.pizza.pork.eval
 
-import gay.pizza.pork.ast.*
+import gay.pizza.pork.ast.NodeVisitor
 import gay.pizza.pork.ast.nodes.*
 
 class Evaluator(root: Scope) : NodeVisitor<Any> {
@@ -102,11 +102,35 @@ class Evaluator(root: Scope) : NodeVisitor<Any> {
     }
   }
 
-  override fun visitProgram(node: Program): Any {
+  override fun visitFunctionDeclaration(node: FunctionDeclaration): Any {
+    val blockFunction = visitBlock(node.block) as BlockFunction
+    val function = CallableFunction { arguments ->
+      currentScope = currentScope.fork()
+      for ((index, argumentSymbol) in node.arguments.withIndex()) {
+        currentScope.define(argumentSymbol.id, arguments.values[index])
+      }
+      try {
+        return@CallableFunction blockFunction.call()
+      } finally {
+        currentScope = currentScope.leave()
+      }
+    }
+    currentScope.define(node.symbol.id, function)
+    return None
+  }
+
+  override fun visitBlock(node: Block): Any = BlockFunction {
     var value: Any? = null
     for (expression in node.expressions) {
       value = visit(expression)
     }
-    return value ?: None
+    value ?: None
+  }
+
+  override fun visitCompilationUnit(node: CompilationUnit): Any {
+    for (declaration in node.declarations) {
+      visit(declaration)
+    }
+    return None
   }
 }

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

@@ -2,7 +2,7 @@ package gay.pizza.pork.frontend
 
 import gay.pizza.pork.ast.NodeVisitor
 import gay.pizza.pork.ast.Printer
-import gay.pizza.pork.ast.nodes.Program
+import gay.pizza.pork.ast.nodes.CompilationUnit
 import gay.pizza.pork.eval.Evaluator
 import gay.pizza.pork.eval.Scope
 import gay.pizza.pork.parse.*
@@ -13,8 +13,8 @@ abstract class Frontend {
   fun tokenize(): TokenStream =
     Tokenizer(createCharSource()).tokenize()
 
-  fun parse(attribution: NodeAttribution = DiscardNodeAttribution): Program =
-    Parser(TokenStreamSource(tokenize()), attribution).readProgram()
+  fun parse(attribution: NodeAttribution = DiscardNodeAttribution): CompilationUnit =
+    Parser(TokenStreamSource(tokenize()), attribution).readCompilationUnit()
 
   fun highlight(scheme: HighlightScheme): List<Highlight> =
     Highlighter(scheme).highlight(tokenize())

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

@@ -160,6 +160,35 @@ class Parser(source: PeekableSource<Token>, val attribution: NodeAttribution) {
     } else expression
   }
 
+  private fun readBlock(): Block = within {
+    expect(TokenType.LeftCurly)
+    val items = collect(TokenType.RightCurly) {
+      readExpression()
+    }
+    expect(TokenType.RightCurly)
+    Block(items)
+  }
+
+  private fun readFunctionDeclaration(): FunctionDeclaration = within {
+    expect(TokenType.Fn)
+    val name = readSymbolRaw()
+    expect(TokenType.LeftParentheses)
+    val arguments = collect(TokenType.RightParentheses, TokenType.Comma) { readSymbolRaw() }
+    expect(TokenType.RightParentheses)
+    FunctionDeclaration(name, arguments, readBlock())
+  }
+
+  fun readDeclaration(): Declaration {
+    val token = peek()
+    return when (token.type) {
+      TokenType.Fn -> readFunctionDeclaration()
+      else -> throw RuntimeException(
+        "Failed to parse token: ${token.type} '${token.text}' as" +
+          " declaration (index ${unsanitizedSource.currentIndex})"
+      )
+    }
+  }
+
   private fun convertInfixOperator(token: Token): InfixOperator =
     when (token.type) {
       TokenType.Plus -> InfixOperator.Plus
@@ -171,10 +200,10 @@ class Parser(source: PeekableSource<Token>, val attribution: NodeAttribution) {
       else -> throw RuntimeException("Unknown Infix Operator")
     }
 
-  fun readProgram(): Program = within {
-    val items = collect(TokenType.EndOfFile) { readExpression() }
+  fun readCompilationUnit(): CompilationUnit = within {
+    val declarations = collect(TokenType.EndOfFile) { readDeclaration() }
     expect(TokenType.EndOfFile)
-    Program(items)
+    CompilationUnit(declarations)
   }
 
   private fun <T> collect(
@@ -209,7 +238,7 @@ class Parser(source: PeekableSource<Token>, val attribution: NodeAttribution) {
     val token = next()
     if (!types.contains(token.type)) {
       throw RuntimeException(
-        "Expected one of ${types.joinToString(", ")} " +
+        "Expected one of ${types.joinToString(", ")}" +
           " but got type ${token.type} '${token.text}'"
       )
     }

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

@@ -28,6 +28,7 @@ enum class TokenType(vararg properties: TokenTypeProperty) {
   If(Keyword("if"), KeywordFamily),
   Then(Keyword("then"), KeywordFamily),
   Else(Keyword("else"), KeywordFamily),
+  Fn(Keyword("fn"), KeywordFamily),
   Whitespace(CharConsumer { it == ' ' || it == '\r' || it == '\n' || it == '\t' }),
   BlockComment(CommentFamily),
   LineComment(CommentFamily),