perf: introduce AST to avoid reparse

src/tokens/literal-token.ts

@@ -0,0 +1,15 @@
+import { Token } from './token'
+import { TokenKind } from '../parser/token-kind'
+
+export class LiteralToken extends Token {
+  public literal: string
+  public constructor (
+    public input: string,
+    public begin: number,
+    public end: number,
+    public file?: string
+  ) {
+    super(TokenKind.Literal, input, begin, end, file)
+    this.literal = this.getText()
+  }
+}