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ast-reducer

0.2.2 • Public • Published

AST Reducer

A Tool to process AST or any other recursive data structure in JavaScript.

Features

  • An EDSL to define reduce rules
  • Pure functional:
    • state is managed via simulating a state monad (the state field in context)
    • global constants is managed via simulating a reader monad (the env field in context)
  • Derivable Reducer
  • Pretty and helpful error message
  • Configuable node parsing logic (the parseNode field in opts)
  • Configuable default rule (the defaultRule field in opts)

Install

npm install ast-reducer

Usage

In CoffeeScript

Simple Usage

{defineReducer} = require('ast-reducer')
 
evalExpr = defineReducer({name: 'ArithCalc'}) (def) ->
  def('+') ([a, b]) -> @(a) + @(b)
  def('-') ([a, b]) -> @(a) - @(b)
  def('const') ([a]) -> parseFloat(a)
 
ast = ['+', ['-', ['const', 1], ['const', 2]], ['+', ['const', '4'], ['const', '8']]]
console.log evalExpr.eval(ast)
 
# output: 11 

Use State

evalExpr = defineReducer({name: 'ArithCalc0'}) (def) ->
  def('+') ([a, b], {env, state}) -> state.cnt += 1; @(a) + @(b)
  def('-') ([a, b], {env, state}) -> state.cnt += 1; @(a) - @(b)
  def('const') ([a]) -> parseFloat(a)
 
context = {env: {}, initState: (-> {cnt: 0})}
console.log evalExpr.runState(ast, context)
 
# output: { result: 11, state: { cnt: 3 } } 

Derive Reducer

evalExpr2 = evalExpr.derive({name: 'ArithCalc1'}) (def) ->
  def('*') ([a, b], {env, state}) -> state.cnt += 1; @(a) * @(b)
 
ast2 = ['+', ['-', ['const', 1], ['const', 2]], ['*', ['const', '4'], ['const', '8']]]
console.log evalExpr2.runState(ast2, context)
 
# output: { result: 31, state: { cnt: 3 } } 

Error Report

console.log evalExpr.runState(ast2, context)
 
### error message:
 
ReduceError:
  [reducer]: "ArithCalc0"
  [path]: ["+","*"]
  [state]: {"cnt":2}
  [current]: ["*",["const","4"],["const","8"]]
  [input]: ["+",["-",["const",1],["const",2]],["*",["const","4"],["const","8"]]]
 
  Caused By: UnimplementedRule: *
      at Function.defaultRule (the/long/long/path/to/reducer.coffee:34:13)
 
    at reduce (the/long/long/path/to/reducer.coffee:42:11)
    at Object.runState (the/long/long/path/to/reducer.coffee:47:31)
    ...
###

Readme

Keywords

Package Sidebar

Install

npm i ast-reducer

Repository

github.com/luochen1990/ast-reducer

Homepage

github.com/luochen1990/ast-reducer#readme

Weekly Downloads

12

Version

0.2.2

License

MIT

Unpacked Size

11 kB

Total Files

5

Last publish

Collaborators

  • luochen1990
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