language: implement list indexing

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

@@ -78,6 +78,10 @@ class Parser(source: TokenSource, attribution: NodeAttribution) :
         val infixOperator = ParserHelpers.convertInfixOperator(infixToken)
         InfixOperation(expression, infixOperator, parseExpression())
       }
+    } else if (next(TokenType.LeftBracket)) {
+      val index = parseExpression()
+      expect(TokenType.RightBracket)
+      IndexedBy(expression, index)
     } else expression
   }
 
@@ -237,6 +241,14 @@ class Parser(source: TokenSource, attribution: NodeAttribution) :
     ImportDeclaration(form, components)
   }
 
+  override fun parseIndexedBy(): IndexedBy = guarded(NodeType.IndexedBy) {
+    val expression = parseExpression()
+    expect(TokenType.LeftBracket)
+    val index = parseExpression()
+    expect(TokenType.RightBracket)
+    IndexedBy(expression, index)
+  }
+
   override fun parseInfixOperation(): InfixOperation = guarded(NodeType.InfixOperation) {
     val infixToken = next()
     val infixOperator = ParserHelpers.convertInfixOperator(infixToken)

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

@@ -233,6 +233,13 @@ class Printer(buffer: StringBuilder) : NodeVisitor<Unit> {
     }
   }
 
+  override fun visitIndexedBy(node: IndexedBy) {
+    visit(node.expression)
+    append("[")
+    visit(node.index)
+    append("]")
+  }
+
   override fun visitCompilationUnit(node: CompilationUnit) {
     for (declaration in node.declarations) {
       visit(declaration)