language: implement let definitions

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

@@ -226,7 +226,7 @@ class Parser(source: PeekableSource<Token>, val attribution: NodeAttribution) {
     ImportDeclaration(form, components)
   }
 
-  private fun readFunctionDeclaration(): FunctionDefinition = within {
+  private fun readDefinitionModifiers(): DefinitionModifiers {
     val modifiers = DefinitionModifiers(export = false)
     while (true) {
       val token = peek()
@@ -238,12 +238,16 @@ class Parser(source: PeekableSource<Token>, val attribution: NodeAttribution) {
         else -> break
       }
     }
+    return modifiers
+  }
+
+  private fun readFunctionDeclaration(modifiers: DefinitionModifiers): FunctionDefinition = within {
     expect(TokenType.Func)
     val name = readSymbolRaw()
     expect(TokenType.LeftParentheses)
     val arguments = collect(TokenType.RightParentheses, TokenType.Comma) {
       val symbol = readSymbolRaw()
-      var multiple: Boolean = false
+      var multiple = false
       if (next(TokenType.DotDotDot)) {
         multiple = true
       }
@@ -261,11 +265,21 @@ class Parser(source: PeekableSource<Token>, val attribution: NodeAttribution) {
     FunctionDefinition(modifiers, name, arguments, block, native)
   }
 
+  private fun readLetDefinition(modifiers: DefinitionModifiers): LetDefinition = within {
+    val modifiers = readDefinitionModifiers()
+    expect(TokenType.Let)
+    val name = readSymbolRaw()
+    expect(TokenType.Equals)
+    val value = readExpression()
+    LetDefinition(modifiers, name, value)
+  }
+
   private fun maybeReadDefinition(): Definition? {
+    val modifiers = readDefinitionModifiers()
     val token = peek()
     return when (token.type) {
-      TokenType.Export,
-      TokenType.Func -> readFunctionDeclaration()
+      TokenType.Func -> readFunctionDeclaration(modifiers)
+      TokenType.Let -> readLetDefinition(modifiers)
       else -> null
     }
   }

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

@@ -91,6 +91,14 @@ class Printer(buffer: StringBuilder) : NodeVisitor<Unit> {
     visit(node.value)
   }
 
+  override fun visitLetDefinition(node: LetDefinition) {
+    visitDefinitionModifiers(node.modifiers)
+    append("let ")
+    visit(node.symbol)
+    append(" = ")
+    visit(node.value)
+  }
+
   override fun visitSymbolReference(node: SymbolReference) {
     visit(node.symbol)
   }
@@ -152,10 +160,14 @@ class Printer(buffer: StringBuilder) : NodeVisitor<Unit> {
     visit(node.right)
   }
 
-  override fun visitFunctionDefinition(node: FunctionDefinition) {
-    if (node.modifiers.export) {
+  private fun visitDefinitionModifiers(modifiers: DefinitionModifiers) {
+    if (modifiers.export) {
       append("export ")
     }
+  }
+
+  override fun visitFunctionDefinition(node: FunctionDefinition) {
+    visitDefinitionModifiers(node.modifiers)
     append("func ")
     visit(node.symbol)
     append("(")