refactor: rewrite expression evaluation, fix #130

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()!
+  }
+}