perf: introduce AST to avoid reparse

src/template/value.ts

@@ -1,23 +1,24 @@
-import { Expression } from '../render/expression'
+import { evalToken } from '../render/expression'
 import { Tokenizer } from '../parser/tokenizer'
 import { FilterMap } from '../template/filter/filter-map'
 import { Filter } from './filter/filter'
 import { Context } from '../context/context'
+import { ValueToken } from '../tokens/value-token'
 
 export class Value {
   public readonly filters: Filter[] = []
-  public readonly initial: string
+  public readonly initial?: ValueToken
 
   /**
    * @param str the value to be valuated, eg.: "foobar" | truncate: 3
    */
   public constructor (str: string, private readonly filterMap: FilterMap) {
     const tokenizer = new Tokenizer(str)
-    this.initial = tokenizer.readValue().toString()
-    this.filters = tokenizer.readFilterTokens().map(({ name, args }) => new Filter(name, this.filterMap.get(name), args))
+    this.initial = tokenizer.readValue()
+    this.filters = tokenizer.readFilters().map(({ name, args }) => new Filter(name, this.filterMap.get(name), args))
   }
   public * value (ctx: Context) {
-    let val = yield new Expression(this.initial).evaluate(ctx)
+    let val = yield evalToken(this.initial, ctx)
     for (const filter of this.filters) {
       val = yield filter.render(val, ctx)
     }