refactor: rewrite expression evaluation, fix #130

src/parser/literal.ts

@@ -0,0 +1,18 @@
+import { last } from '../util/underscore'
+import { NullDrop } from '../drop/null-drop'
+import { EmptyDrop } from '../drop/empty-drop'
+import { BlankDrop } from '../drop/blank-drop'
+
+type literal = true | false | NullDrop | EmptyDrop | BlankDrop | number | string
+
+export function parseLiteral (str: string): literal | undefined {
+  str = str.trim()
+
+  if (str === 'true') return true
+  if (str === 'false') return false
+  if (str === 'nil' || str === 'null') return new NullDrop()
+  if (str === 'empty') return new EmptyDrop()
+  if (str === 'blank') return new BlankDrop()
+  if (!isNaN(Number(str))) return Number(str)
+  if ((str[0] === '"' || str[0] === "'") && str[0] === last(str)) return str.slice(1, -1)
+}