refactor: rewrite expression evaluation, fix #130

src/builtin/filters/array.ts

@@ -1,5 +1,5 @@
 import { isArray, last } from '../../util/underscore'
-import { isTruthy } from '../../render/syntax'
+import { isTruthy } from '../../render/boolean'
 
 export default {
   'join': (v: any[], arg: string) => v.join(arg === undefined ? ' ' : arg),

src/builtin/filters/object.ts

@@ -1,4 +1,4 @@
-import { isFalsy } from '../../render/syntax'
+import { isFalsy } from '../../render/boolean'
 import { toValue } from '../../util/underscore'
 
 export default {

src/builtin/tags/assign.ts

@@ -1,8 +1,6 @@
 import { assert } from '../../util/assert'
 import { identifier } from '../../parser/lexical'
-import { TagToken } from '../../parser/tag-token'
+import { ITagImplOptions, TagToken, Context } from '../../types'
-import { Context } from '../../context/context'
-import { ITagImplOptions } from '../../template/tag/itag-impl-options'
 
 const re = new RegExp(`(${identifier.source})\\s*=([^]*)`)
 

src/builtin/tags/case.ts

@@ -1,5 +1,4 @@
-import { Hash, Emitter, TagToken, Token, Context, ITemplate, ITagImplOptions, ParseStream } from '../../types'
+import { Expression, Hash, Emitter, TagToken, Token, Context, ITemplate, ITagImplOptions, ParseStream } from '../../types'
-import { evalExp } from '../../render/syntax'
 
 export default {
   parse: function (tagToken: TagToken, remainTokens: Token[]) {
@@ -28,8 +27,8 @@ export default {
   render: async function (ctx: Context, hash: Hash, emitter: Emitter) {
     for (let i = 0; i < this.cases.length; i++) {
       const branch = this.cases[i]
-      const val = await evalExp(branch.val, ctx)
+      const val = new Expression(branch.val).value(ctx)
-      const cond = await evalExp(this.cond, ctx)
+      const cond = new Expression(this.cond).value(ctx)
       if (val === cond) {
         this.liquid.renderer.renderTemplates(branch.templates, ctx, emitter)
         return

src/builtin/tags/cycle.ts

@@ -1,6 +1,6 @@
 import { assert } from '../../util/assert'
 import { value as rValue } from '../../parser/lexical'
-import { evalValue } from '../../render/syntax'
+import { Expression } from '../../render/expression'
 import { TagToken } from '../../parser/tag-token'
 import { Context } from '../../context/context'
 import { ITagImplOptions } from '../../template/tag/itag-impl-options'
@@ -13,7 +13,7 @@ export default {
     let match: RegExpExecArray | null = groupRE.exec(tagToken.args) as RegExpExecArray
     assert(match, `illegal tag: ${tagToken.raw}`)
 
-    this.group = match[1] || ''
+    this.group = new Expression(match[1])
     const candidates = match[2]
 
     this.candidates = []
@@ -25,7 +25,7 @@ export default {
   },
 
   render: async function (ctx: Context) {
-    const group = await evalValue(this.group, ctx)
+    const group = this.group.value(ctx)
     const fingerprint = `cycle:${group}:` + this.candidates.join(',')
     const groups = ctx.getRegister('cycle')
     let idx = groups[fingerprint]
@@ -38,6 +38,6 @@ export default {
     idx = (idx + 1) % this.candidates.length
     groups[fingerprint] = idx
 
-    return evalValue(candidate, ctx)
+    return new Expression(candidate).value(ctx)
   }
 } as ITagImplOptions

src/builtin/tags/for.ts

@@ -1,6 +1,6 @@
 import { Emitter, TagToken, Token, Context, ITemplate, ITagImplOptions, ParseStream } from '../../types'
 import { isString, isObject, isArray } from '../../util/underscore'
-import { parseExp } from '../../render/syntax'
+import { Expression } from '../../render/expression'
 import { assert } from '../../util/assert'
 import { identifier, value, hash } from '../../parser/lexical'
 import { ForloopDrop } from '../../drop/forloop-drop'
@@ -37,7 +37,7 @@ export default {
     stream.start()
   },
   render: async function (ctx: Context, hash: Hash, emitter: Emitter) {
-    let collection = await parseExp(this.collection, ctx)
+    let collection = new Expression(this.collection).value(ctx)
 
     if (!isArray(collection)) {
       if (isString(collection) && collection.length > 0) {

src/builtin/tags/if.ts

@@ -1,4 +1,4 @@
-import { Hash, Emitter, evalExp, isTruthy, TagToken, Token, Context, ITemplate, ITagImplOptions, ParseStream } from '../../types'
+import { Hash, Emitter, isTruthy, Expression, TagToken, Token, Context, ITemplate, ITagImplOptions, ParseStream } from '../../types'
 
 export default {
   parse: function (tagToken: TagToken, remainTokens: Token[]) {
@@ -29,7 +29,7 @@ export default {
 
   render: async function (ctx: Context, hash: Hash, emitter: Emitter) {
     for (const branch of this.branches) {
-      const cond = await evalExp(branch.cond, ctx)
+      const cond = new Expression(branch.cond).value(ctx)
       if (isTruthy(cond)) {
         await this.liquid.renderer.renderTemplates(branch.templates, ctx, emitter)
         return

src/builtin/tags/include.ts

@@ -1,7 +1,6 @@
 import { assert } from '../../util/assert'
-import { Hash, Emitter, TagToken, Context, ITagImplOptions } from '../../types'
+import { Expression, Hash, Emitter, TagToken, Context, ITagImplOptions } from '../../types'
 import { value, quotedLine } from '../../parser/lexical'
-import { evalValue, parseValue } from '../../render/syntax'
 import BlockMode from '../../context/block-mode'
 
 const staticFileRE = /[^\s,]+/
@@ -25,7 +24,7 @@ export default {
         const template = this.value.slice(1, -1)
         filepath = await this.liquid.parseAndRender(template, ctx.getAll(), ctx.opts)
       } else {
-        filepath = await evalValue(this.value, ctx)
+        filepath = new Expression(this.value).value(ctx)
       }
     } else {
       filepath = this.staticValue
@@ -38,7 +37,7 @@ export default {
     ctx.setRegister('blocks', {})
     ctx.setRegister('blockMode', BlockMode.OUTPUT)
     if (this.with) {
-      hash[filepath] = await parseValue(this.with, ctx)
+      hash[filepath] = new Expression(this.with).evaluate(ctx)
     }
     const templates = await this.liquid.getTemplate(filepath, ctx.opts)
     ctx.push(hash)

src/builtin/tags/layout.ts

@@ -1,7 +1,6 @@
 import { assert } from '../../util/assert'
 import { value as rValue } from '../../parser/lexical'
-import { evalValue } from '../../render/syntax'
+import { Expression, TagToken, Token, Context, ITagImplOptions } from '../../types'
-import { TagToken, Token, Context, ITagImplOptions } from '../../types'
 import BlockMode from '../../context/block-mode'
 import { Hash } from '../../template/tag/hash'
 
@@ -23,7 +22,7 @@ export default {
   },
   render: async function (ctx: Context, hash: Hash) {
     const layout = ctx.opts.dynamicPartials
-      ? await evalValue(this.layout, ctx)
+      ? await (new Expression(this.layout).value(ctx))
       : this.staticLayout
     assert(layout, `cannot apply layout with empty filename`)
 

src/builtin/tags/tablerow.ts

@@ -1,5 +1,5 @@
 import { assert } from '../../util/assert'
-import { evalExp, Emitter, Hash, TagToken, Token, Context, ITemplate, ITagImplOptions, ParseStream } from '../../types'
+import { Expression, Emitter, Hash, TagToken, Token, Context, ITemplate, ITagImplOptions, ParseStream } from '../../types'
 import { identifier, value, hash } from '../../parser/lexical'
 import { TablerowloopDrop } from '../../drop/tablerowloop-drop'
 
@@ -29,7 +29,7 @@ export default {
   },
 
   render: async function (ctx: Context, hash: Hash, emitter: Emitter) {
-    let collection = await evalExp(this.collection, ctx) || []
+    let collection = new Expression(this.collection).value(ctx) || []
     const offset = hash.offset || 0
     const limit = (hash.limit === undefined) ? collection.length : hash.limit
 

src/builtin/tags/unless.ts

@@ -1,4 +1,4 @@
-import { Emitter, evalExp, isFalsy, ParseStream, Context, ITagImplOptions, Token, Hash, TagToken } from '../../types'
+import { Emitter, Expression, isFalsy, ParseStream, Context, ITagImplOptions, Token, Hash, TagToken } from '../../types'
 
 export default {
   parse: function (tagToken: TagToken, remainTokens: Token[]) {
@@ -21,7 +21,7 @@ export default {
   },
 
   render: async function (ctx: Context, hash: Hash, emitter: Emitter) {
-    const cond = await evalExp(this.cond, ctx)
+    const cond = new Expression(this.cond).value(ctx)
     isFalsy(cond)
       ? await this.liquid.renderer.renderTemplates(this.templates, ctx, emitter)
       : await this.liquid.renderer.renderTemplates(this.elseTemplates, ctx, emitter)

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)
+}

src/render/boolean.ts

@@ -0,0 +1,6 @@
+export function isTruthy (val: any): boolean {
+  return !isFalsy(val)
+}
+export function isFalsy (val: any): boolean {
+  return val === false || undefined === val || val === null
+}

src/render/expression.ts

@@ -0,0 +1,82 @@
+import { assert } from '../util/assert'
+import { isRange, rangeValue } from './range'
+import { Value } from './value'
+import { Context } from '../context/context'
+import { toValue } from '../util/underscore'
+import { isOperator, precedence, operatorImpls } from './operator'
+
+export class Expression {
+  private str: string
+
+  public constructor (str: string = '') {
+    this.str = str
+  }
+  public evaluate (ctx: Context): any {
+    assert(ctx, 'unable to evaluate: context not defined')
+
+    const operands = []
+    for (const token of toPostfix(this.str)) {
+      if (isOperator(token)) {
+        const r = operands.pop()
+        const l = operands.pop()
+        const result = operatorImpls[token](l, r)
+        operands.push(result)
+        continue
+      }
+      if (isRange(token)) {
+        operands.push(rangeValue(token, ctx))
+        continue
+      }
+      operands.push(new Value(token).evaluate(ctx))
+    }
+    return operands[0]
+  }
+  public value (ctx: Context): any {
+    return toValue(this.evaluate(ctx))
+  }
+}
+
+function * tokenize (expr: string): IterableIterator<string> {
+  const N = expr.length
+  let str = ''
+  const pairs = { '"': '"', "'": "'", '[': ']', '(': ')' }
+
+  for (let i = 0; i < N; i++) {
+    const c = expr[i]
+    switch (c) {
+      case '[':
+      case '"':
+      case "'":
+        str += c
+        while (i + 1 < N) {
+          str += expr[++i]
+          if (expr[i] === pairs[c]) break
+        }
+        break
+      case ' ':
+      case '\t':
+      case '\n':
+        if (str) yield str
+        str = ''
+        break
+      default:
+        str += c
+    }
+  }
+  if (str) yield str
+}
+
+function * toPostfix (expr: string): IterableIterator<string> {
+  const ops = []
+  for (const token of tokenize(expr)) {
+    if (isOperator(token)) {
+      while (ops.length && precedence[ops[ops.length - 1]] > precedence[token]) {
+        yield ops.pop()!
+      }
+      ops.push(token)
+    } else yield token
+  }
+  while (ops.length) {
+    yield ops.pop()!
+  }
+}

src/render/operator.ts

@@ -0,0 +1,59 @@
+import { isComparable } from '../drop/icomparable'
+import { isFunction } from '../util/underscore'
+import { isTruthy } from '../render/boolean'
+
+export const precedence = {
+  '==': 1,
+  '!=': 1,
+  '>': 1,
+  '<': 1,
+  '>=': 1,
+  '<=': 1,
+  'contains': 1,
+  'and': 0,
+  'or': 0
+}
+
+export const operatorImpls: {[key: string]: (lhs: any, rhs: any) => boolean} = {
+  '==': (l: any, r: any) => {
+    if (isComparable(l)) return l.equals(r)
+    if (isComparable(r)) return r.equals(l)
+    return l === r
+  },
+  '!=': (l: any, r: any) => {
+    if (isComparable(l)) return !l.equals(r)
+    if (isComparable(r)) return !r.equals(l)
+    return l !== r
+  },
+  '>': (l: any, r: any) => {
+    if (isComparable(l)) return l.gt(r)
+    if (isComparable(r)) return r.lt(l)
+    return l > r
+  },
+  '<': (l: any, r: any) => {
+    if (isComparable(l)) return l.lt(r)
+    if (isComparable(r)) return r.gt(l)
+    return l < r
+  },
+  '>=': (l: any, r: any) => {
+    if (isComparable(l)) return l.geq(r)
+    if (isComparable(r)) return r.leq(l)
+    return l >= r
+  },
+  '<=': (l: any, r: any) => {
+    if (isComparable(l)) return l.leq(r)
+    if (isComparable(r)) return r.geq(l)
+    return l <= r
+  },
+  'contains': (l: any, r: any) => {
+    return l && isFunction(l.indexOf) ? l.indexOf(r) > -1 : false
+  },
+  'and': (l: any, r: any) => isTruthy(l) && isTruthy(r),
+  'or': (l: any, r: any) => isTruthy(l) || isTruthy(r)
+}
+
+const list = Object.keys(precedence)
+
+export function isOperator (token: string) {
+  return list.includes(token)
+}

src/render/range.ts

@@ -0,0 +1,17 @@
+import { rangeLine } from '../parser/lexical'
+import { Context } from '../context/context'
+import { range } from '../util/underscore'
+import { Value } from './value'
+
+export function isRange (token: string = '') {
+  return token[0] === '(' && token[token.length - 1] === ')'
+}
+
+export function rangeValue (token: string = '', ctx: Context) {
+  let match
+  if ((match = token.match(rangeLine))) {
+    const low = new Value(match[1]).value(ctx)
+    const high = new Value(match[2]).value(ctx)
+    return range(+low, +high + 1)
+  }
+}

src/render/syntax.ts

@@ -1,100 +0,0 @@
-import * as lexical from '../parser/lexical'
-import { assert } from '../util/assert'
-import { Context } from '../context/context'
-import { range, last, isFunction, toValue } from '../util/underscore'
-import { isComparable } from '../drop/icomparable'
-import { NullDrop } from '../drop/null-drop'
-import { EmptyDrop } from '../drop/empty-drop'
-import { BlankDrop } from '../drop/blank-drop'
-
-const binaryOperators: {[key: string]: (lhs: any, rhs: any) => boolean} = {
-  '==': (l: any, r: any) => {
-    if (isComparable(l)) return l.equals(r)
-    if (isComparable(r)) return r.equals(l)
-    return l === r
-  },
-  '!=': (l: any, r: any) => {
-    if (isComparable(l)) return !l.equals(r)
-    if (isComparable(r)) return !r.equals(l)
-    return l !== r
-  },
-  '>': (l: any, r: any) => {
-    if (isComparable(l)) return l.gt(r)
-    if (isComparable(r)) return r.lt(l)
-    return l > r
-  },
-  '<': (l: any, r: any) => {
-    if (isComparable(l)) return l.lt(r)
-    if (isComparable(r)) return r.gt(l)
-    return l < r
-  },
-  '>=': (l: any, r: any) => {
-    if (isComparable(l)) return l.geq(r)
-    if (isComparable(r)) return r.leq(l)
-    return l >= r
-  },
-  '<=': (l: any, r: any) => {
-    if (isComparable(l)) return l.leq(r)
-    if (isComparable(r)) return r.geq(l)
-    return l <= r
-  },
-  'contains': (l: any, r: any) => {
-    return l && isFunction(l.indexOf) ? l.indexOf(r) > -1 : false
-  },
-  'and': (l: any, r: any) => isTruthy(l) && isTruthy(r),
-  'or': (l: any, r: any) => isTruthy(l) || isTruthy(r)
-}
-
-export function parseExp (exp: string, ctx: Context): any {
-  assert(ctx, 'unable to parseExp: 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 = parseExp(match[1], ctx)
-      const op = binaryOperators[match[2].trim()]
-      const r = parseExp(match[3], ctx)
-      return op(l, r)
-    }
-  }
-
-  if ((match = exp.match(lexical.rangeLine))) {
-    const low = evalValue(match[1], ctx)
-    const high = evalValue(match[2], ctx)
-    return range(+low, +high + 1)
-  }
-
-  return parseValue(exp, ctx)
-}
-
-export function evalExp (str: string, ctx: Context): any {
-  return toValue(parseExp(str, ctx))
-}
-
-export function parseValue (str: string | undefined, ctx: Context): any {
-  if (!str) return null
-  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)
-  return ctx.get(str)
-}
-
-export function evalValue (str: string | undefined, ctx: Context) {
-  return toValue(parseValue(str, ctx))
-}
-
-export function isTruthy (val: any): boolean {
-  return !isFalsy(val)
-}
-
-export function isFalsy (val: any): boolean {
-  return val === false || undefined === val || val === null
-}

src/render/value.ts

@@ -0,0 +1,23 @@
+import { toValue } from '../util/underscore'
+import { Context } from '../context/context'
+import { parseLiteral } from '../parser/literal'
+
+export class Value {
+  private str: string
+
+  public constructor (str: string = '') {
+    this.str = str
+  }
+
+  public evaluate (ctx: Context) {
+    const literalValue = parseLiteral(this.str)
+    if (literalValue !== undefined) {
+      return literalValue
+    }
+    return ctx.get(this.str)
+  }
+
+  public value (ctx: Context) {
+    return toValue(this.evaluate(ctx))
+  }
+}

src/template/filter/filter.ts

@@ -1,4 +1,4 @@
-import { parseValue } from '../../render/syntax'
+import { Expression } from '../../render/expression'
 import { Context } from '../../context/context'
 import { isArray } from '../../util/underscore'
 import { FilterImplOptions } from './filter-impl-options'
@@ -24,8 +24,8 @@ export class Filter {
   public render (value: any, context: Context) {
     const argv: any[] = []
     for (const arg of this.args) {
-      if (isKeyValuePair(arg)) argv.push([arg[0], parseValue(arg[1], context)])
+      if (isKeyValuePair(arg)) argv.push([arg[0], new Expression(arg[1]).evaluate(context)])
-      else argv.push(parseValue(arg, context))
+      else argv.push(new Expression(arg).evaluate(context))
     }
     return this.impl.apply({ context }, [value, ...argv])
   }

src/template/tag/hash.ts

@@ -1,5 +1,5 @@
 import { hashCapture } from '../../parser/lexical'
-import { parseValue } from '../../render/syntax'
+import { Expression } from '../../render/expression'
 import { Context } from '../../context/context'
 
 /**
@@ -17,7 +17,7 @@ export class Hash {
     while ((match = hashCapture.exec(markup))) {
       const k = match[1]
       const v = match[2]
-      instance[k] = await parseValue(v, ctx)
+      instance[k] = new Expression(v).evaluate(ctx)
     }
     return instance
   }

src/template/value.ts

@@ -1,4 +1,4 @@
-import { parseExp } from '../render/syntax'
+import { Expression } from '../render/expression'
 import { FilterArgs, Filter } from './filter/filter'
 import { Context } from '../context/context'
 
@@ -48,7 +48,7 @@ export class Value {
     this.filters.push(new Filter(name, args, this.strictFilters))
   }
   public value (ctx: Context) {
-    let val = parseExp(this.initial, ctx)
+    let val = new Expression(this.initial).evaluate(ctx)
     for (const filter of this.filters) {
       val = filter.render(val, ctx)
     }

src/types.ts

@@ -1,7 +1,8 @@
 export { ParseError, TokenizationError, RenderBreakError, AssertionError } from './util/error'
 export { Drop } from './drop/drop'
 export { Emitter } from './render/emitter'
-export { isTruthy, isFalsy, evalExp, evalValue } from './render/syntax'
+export { Expression } from './render/expression'
+export { isFalsy, isTruthy } from './render/boolean'
 export { TagToken } from './parser/tag-token'
 export { Context } from './context/context'
 export { ITemplate } from './template/itemplate'

test/e2e/eval-value.ts

@@ -6,6 +6,6 @@ describe('.evalValue()', function () {
   beforeEach(() => { engine = new Liquid() })
 
   it('should throw when scope undefined', async function () {
-    return expect(() => engine.evalValue('{{"foo"}}', null as any)).to.throw(/scope undefined/)
+    return expect(() => engine.evalValue('{{"foo"}}', null as any)).to.throw(/context not defined/)
   })
 })

test/integration/builtin/tags/if.ts

@@ -60,6 +60,11 @@ describe('tags/if', function () {
       const html = await liquid.parseAndRender(src, ctx)
       return expect(html).to.equal('XY')
     })
+    it('should evaluate right to left', async function () {
+      const src = `{% if false and false or true %}true{%endif%}`
+      const html = await liquid.parseAndRender(src)
+      return expect(html).to.equal('')
+    })
   })
   describe('comparasion to null', function () {
     it('should evaluate false for null < 10', async function () {

test/unit/parser/literal.ts

@@ -0,0 +1,27 @@
+import { expect } from 'chai'
+import { parseLiteral } from '../../../src/parser/literal'
+import { NullDrop } from '../../../src/drop/null-drop'
+
+describe('parseLiteral', function () {
+  it('should eval boolean literal', async function () {
+    expect(parseLiteral('true')).to.equal(true)
+    expect(parseLiteral('TrUE')).to.equal(undefined)
+    expect(parseLiteral('false')).to.equal(false)
+  })
+  it('should eval number literal', async function () {
+    expect(parseLiteral('2.3')).to.equal(2.3)
+    expect(parseLiteral('.32')).to.equal(0.32)
+    expect(parseLiteral('-23.')).to.equal(-23)
+    expect(parseLiteral('23')).to.equal(23)
+  })
+  it('should eval string literal', async function () {
+    expect(parseLiteral('"ab\'c"')).to.equal("ab'c")
+    expect(parseLiteral("'ab\"c'")).to.equal('ab"c')
+  })
+  it('should eval nil literal', async function () {
+    expect(parseLiteral('nil')).to.be.instanceOf(NullDrop)
+  })
+  it('should eval null literal', async function () {
+    expect(parseLiteral('null')).to.be.instanceOf(NullDrop)
+  })
+})

test/unit/render/boolean.ts

@@ -0,0 +1,38 @@
+import { isTruthy } from '../../../src/render/boolean'
+import { expect } from 'chai'
+
+describe('boolean', async function () {
+  describe('.isTruthy()', async function () {
+    // Spec: https://shopify.github.io/liquid/basics/truthy-and-falsy/
+    it('true is truthy', function () {
+      expect(isTruthy(true)).to.be.true
+    })
+    it('false is falsy', function () {
+      expect(isTruthy(false)).to.be.false
+    })
+    it('null is falsy', function () {
+      expect(isTruthy(null)).to.be.false
+    })
+    it('"foo" is truthy', function () {
+      expect(isTruthy('foo')).to.be.true
+    })
+    it('"" is truthy', function () {
+      expect(isTruthy('')).to.be.true
+    })
+    it('0 is truthy', function () {
+      expect(isTruthy(0)).to.be.true
+    })
+    it('1 is truthy', function () {
+      expect(isTruthy(1)).to.be.true
+    })
+    it('1.1 is truthy', function () {
+      expect(isTruthy(1.1)).to.be.true
+    })
+    it('[1] is truthy', function () {
+      expect(isTruthy([1])).to.be.true
+    })
+    it('[] is truthy', function () {
+      expect(isTruthy([])).to.be.true
+    })
+  })
+})

test/unit/render/expression.ts

@@ -0,0 +1,67 @@
+import { Expression } from '../../../src/render/expression'
+import { expect } from 'chai'
+import { Context } from '../../../src/context/context'
+
+describe('Expression', function () {
+  let ctx: Context
+
+  beforeEach(function () {
+    ctx = new Context({
+      one: 1,
+      two: 2,
+      empty: '',
+      x: 'XXX',
+      y: undefined,
+      z: null
+    })
+  })
+
+  it('should throw when context not defined', async function () {
+    return expect(() => new Expression().value()).to.throw(/context not defined/)
+  })
+
+  it('should eval simple expression', async function () {
+    expect(new Expression('1 < 2').value(ctx)).to.equal(true)
+    expect(new Expression('2 <= 2').value(ctx)).to.equal(true)
+    expect(new Expression('one <= two').value(ctx)).to.equal(true)
+    expect(new Expression('x contains "x"').value(ctx)).to.equal(false)
+    expect(new Expression('x contains "X"').value(ctx)).to.equal(true)
+    expect(new Expression('1 contains "x"').value(ctx)).to.equal(false)
+    expect(new Expression('y contains "x"').value(ctx)).to.equal(false)
+    expect(new Expression('z contains "x"').value(ctx)).to.equal(false)
+    expect(new Expression('(1..5) contains 3').value(ctx)).to.equal(true)
+    expect(new Expression('(1..5) contains 6').value(ctx)).to.equal(false)
+    expect(new Expression('"<=" == "<="').value(ctx)).to.equal(true)
+  })
+
+  describe('complex expression', function () {
+    it('should support value or value', async function () {
+      expect(new Expression('false or true').value(ctx)).to.equal(true)
+    })
+    it('should support < and contains', async function () {
+      expect(new Expression('1 < 2 and x contains "x"').value(ctx)).to.equal(false)
+    })
+    it('should support < or contains', async function () {
+      expect(new Expression('1 < 2 or x contains "x"').value(ctx)).to.equal(true)
+    })
+    it('should support value and !=', async function () {
+      expect(new Expression('empty and empty != ""').value(ctx)).to.equal(false)
+    })
+    it('should recognize quoted value', async function () {
+      expect(new Expression('">"').value(ctx)).to.equal('>')
+    })
+    it('should evaluate from right to left', function () {
+      expect(new Expression('true or false and false').value(ctx)).to.equal(true)
+      expect(new Expression('true and false and false or true').value(ctx)).to.equal(false)
+    })
+    it('should recognize property access', function () {
+      const ctx = new Context({ obj: { foo: true } })
+      expect(new Expression('obj["foo"] and true').value(ctx)).to.equal(true)
+    })
+  })
+
+  it('should eval range expression', async function () {
+    expect(new Expression('(2..4)').value(ctx)).to.deep.equal([2, 3, 4])
+    expect(new Expression('(two..4)').value(ctx)).to.deep.equal([2, 3, 4])
+  })
+})

test/unit/render/syntax.ts

@@ -1,102 +0,0 @@
-import { Context } from '../../../src/context/context'
-import { expect } from 'chai'
-import { evalExp, evalValue, isTruthy } from '../../../src/render/syntax'
-
-describe('render/syntax', function () {
-  let ctx: Context
-
-  beforeEach(function () {
-    ctx = new Context({
-      one: 1,
-      two: 2,
-      empty: '',
-      x: 'XXX',
-      y: undefined,
-      z: null,
-      'has_value?': true
-    })
-  })
-
-  describe('.evalValue()', function () {
-    it('should eval boolean literal', async function () {
-      expect(await evalValue('true', ctx)).to.equal(true)
-      expect(await evalValue('TrUE', ctx)).to.equal(undefined)
-      expect(await evalValue('false', ctx)).to.equal(false)
-    })
-    it('should eval number literal', async function () {
-      expect(await evalValue('2.3', ctx)).to.equal(2.3)
-      expect(await evalValue('.32', ctx)).to.equal(0.32)
-      expect(await evalValue('-23.', ctx)).to.equal(-23)
-      expect(await evalValue('23', ctx)).to.equal(23)
-    })
-    it('should eval string literal', async function () {
-      expect(await evalValue('"ab\'c"', ctx)).to.equal("ab'c")
-      expect(await evalValue("'ab\"c'", ctx)).to.equal('ab"c')
-    })
-    it('should eval nil literal', async function () {
-      expect(await evalValue('nil', ctx)).to.be.null
-    })
-    it('should eval null literal', async function () {
-      expect(await evalValue('null', ctx)).to.be.null
-    })
-    it('should eval scope variables', async function () {
-      expect(await evalValue('one', ctx)).to.equal(1)
-      expect(await evalValue('has_value?', ctx)).to.equal(true)
-      expect(await evalValue('x', ctx)).to.equal('XXX')
-    })
-  })
-
-  describe('.isTruthy()', async function () {
-    // Spec: https://shopify.github.io/liquid/basics/truthy-and-falsy/
-    expect(isTruthy(true)).to.be.true
-    expect(isTruthy(false)).to.be.false
-    expect(isTruthy(null)).to.be.false
-    expect(isTruthy('foo')).to.be.true
-    expect(isTruthy('')).to.be.true
-    expect(isTruthy(0)).to.be.true
-    expect(isTruthy(1)).to.be.true
-    expect(isTruthy(1.1)).to.be.true
-    expect(isTruthy([1])).to.be.true
-    expect(isTruthy([])).to.be.true
-  })
-
-  describe('.evalExp()', function () {
-    it('should throw when scope undefined', async function () {
-      return expect(() => (evalExp as any)('')).to.throw(/scope undefined/)
-    })
-
-    it('should eval simple expression', async function () {
-      expect(await evalExp('1<2', ctx)).to.equal(true)
-      expect(await evalExp('2<=2', ctx)).to.equal(true)
-      expect(await evalExp('one<=two', ctx)).to.equal(true)
-      expect(await evalExp('x contains "x"', ctx)).to.equal(false)
-      expect(await evalExp('x contains "X"', ctx)).to.equal(true)
-      expect(await evalExp('1 contains "x"', ctx)).to.equal(false)
-      expect(await evalExp('y contains "x"', ctx)).to.equal(false)
-      expect(await evalExp('z contains "x"', ctx)).to.equal(false)
-      expect(await evalExp('(1..5) contains 3', ctx)).to.equal(true)
-      expect(await evalExp('(1..5) contains 6', ctx)).to.equal(false)
-      expect(await evalExp('"<=" == "<="', ctx)).to.equal(true)
-    })
-
-    describe('complex expression', function () {
-      it('should support value or value', async function () {
-        expect(await evalExp('false or true', ctx)).to.equal(true)
-      })
-      it('should support < and contains', async function () {
-        expect(await evalExp('1<2 and x contains "x"', ctx)).to.equal(false)
-      })
-      it('should support < or contains', async function () {
-        expect(await evalExp('1<2 or x contains "x"', ctx)).to.equal(true)
-      })
-      it('should support value and !=', async function () {
-        expect(await evalExp('empty and empty != ""', ctx)).to.equal(false)
-      })
-    })
-
-    it('should eval range expression', async function () {
-      expect(await evalExp('(2..4)', ctx)).to.deep.equal([2, 3, 4])
-      expect(await evalExp('(two..4)', ctx)).to.deep.equal([2, 3, 4])
-    })
-  })
-})

test/unit/render/value.ts

@@ -0,0 +1,24 @@
+import { Value } from '../../../src/render/value'
+import { Context } from '../../../src/context/context'
+import { expect } from 'chai'
+
+describe('Value', function () {
+  it('should eval number variable', async function () {
+    const ctx = new Context({ one: 1 })
+    expect(new Value('one').value(ctx)).to.equal(1)
+  })
+  it('question mark should be valid variable name', async function () {
+    const ctx = new Context({ 'has_value?': true })
+    expect(new Value('has_value?').value(ctx)).to.equal(true)
+  })
+  it('should eval string variable', async function () {
+    const ctx = new Context({ x: 'XXX' })
+    expect(new Value('x').value(ctx)).to.equal('XXX')
+  })
+  it('should eval null literal', async function () {
+    expect(new Value('null').value({})).to.be.null
+  })
+  it('should eval nil literal', async function () {
+    expect(new Value('nil').value({})).to.be.null
+  })
+})

tsconfig.json

@@ -8,6 +8,7 @@
     "declaration": true,
     "allowSyntheticDefaultImports": true,
     "resolveJsonModule": true,
+    "downlevelIteration": true,
     "strict": true,
     "suppressImplicitAnyIndexErrors": true
   },