chore(TypeScript): refactor objects into classes

fix: `Nil`(null, undefined) now renders as empty string
change: `parser.parseValue()` renamed to `parser.parseOutput`
change: registered tags/filters become static and shared across different liquid instances

src/render/syntax.ts

@@ -0,0 +1,67 @@
+import * as lexical from '../parser/lexical'
+import assert from '../util/assert'
+
+const operators = {
+  '==': (l, r) => l === r,
+  '!=': (l, r) => l !== r,
+  '>': (l, r) => l !== null && r !== null && l > r,
+  '<': (l, r) => l !== null && r !== null && l < r,
+  '>=': (l, r) => l !== null && r !== null && l >= r,
+  '<=': (l, r) => l !== null && r !== null && l <= r,
+  'contains': (l, r) => {
+    if (!l) return false
+    if (typeof l.indexOf !== 'function') return false
+    return l.indexOf(r) > -1
+  },
+  'and': (l, r) => isTruthy(l) && isTruthy(r),
+  'or': (l, r) => isTruthy(l) || isTruthy(r)
+}
+
+export function evalExp (exp, scope) {
+  assert(scope, 'unable to evalExp: scope undefined')
+  const operatorREs = lexical.operators
+  let match
+  for (let i = 0; i < operatorREs.length; i++) {
+    const operatorRE = operatorREs[i]
+    const expRE = new RegExp(`^(${lexical.quoteBalanced.source})(${operatorRE.source})(${lexical.quoteBalanced.source})$`)
+    if ((match = exp.match(expRE))) {
+      const l = evalExp(match[1], scope)
+      const op = operators[match[2].trim()]
+      const r = evalExp(match[3], scope)
+      return op(l, r)
+    }
+  }
+
+  if ((match = exp.match(lexical.rangeLine))) {
+    const low = evalValue(match[1], scope)
+    const high = evalValue(match[2], scope)
+    const range = []
+    for (let j = low; j <= high; j++) {
+      range.push(j)
+    }
+    return range
+  }
+
+  return evalValue(exp, scope)
+}
+
+export function evalValue (str, scope) {
+  str = str && str.trim()
+  if (!str) return undefined
+
+  if (lexical.isLiteral(str)) {
+    return lexical.parseLiteral(str)
+  }
+  if (lexical.isVariable(str)) {
+    return scope.get(str)
+  }
+  throw new TypeError(`cannot eval '${str}' as value`)
+}
+
+export function isTruthy (val) {
+  return !isFalsy(val)
+}
+
+export function isFalsy (val) {
+  return val === false || undefined === val || val === null
+}