tree-reduce

Reducible tree walk for an arbitrary data structures

npm install tree-reduce
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tree-reduce

Build Status

Reducible tree walk for an arbitrary data structures.

API

tree(form, isBranch, nodes)

Function takes arbitrary data structure as a form argument and returns reducible tree, that can be walked via reduce. Since such trees are reducible that also makes them filter-able, map-able etc... Basically all the reducer functions can be used. To define a tree structure for navigation two other arguments need to be supplied:

  • isBranch predicate function that is invoked on every node and is supposed to return true if node is branch or false otherwise.

  • nodes function invoked on every branch node (nodes to which isBranch returns true) and is expected to return reducible collection of the child nodes.

Please note that tree won't attempt to normalize order of child nodes during recursively walk. More simply if results of nodes function are eventual collections like Stream that emit data asynchronously order of nodes being walked will depend on order in which those nodes arrive. If sequential walk order is desired but underlying data structures are asynchronous it's up to consumer to sequentialize form before passing it to tree.

var tree = require("tree-reduce")
var filter = require("reducers/filter")
var map = require("reducers/map")

function isObject(value) { return value && typeof(value) === "object" }
function values(dictionary) {
  return Object.keys(dictionary).map(function(key) {
    return dictionary[key]
  })
}

// Make reducible AST tree of the source. If node is an object than it's
// a branch.
var ast = tree(esprima.parse(source), isObject, function nodes(form) {
  return values(form).filter(isObject).map(function(node) {
    // Add non-enumerable `parent` property to each node so that path to
    // global scope can be simply obtained. Define `parent` as non-enumerable
    // so it won't show up in `Object.keys` & won't be traversed again.
    Object.defineProperty(node, "parent", {
      parent: { value: form, enumerable: false }
    })
  })
})

// Find all the identifier nodes in the AST.
var allIdentifiers = filter(ast, function(node) {
  return node.type === esprima.Syntax.Identifier
})

// Accumulate only unique identifiers.
var uniqueIdentifiers = fold(allIdentifiers, function(node, unique) {
  var name = node.name
  var contains = unique.some(function(node) { return node.name === name })
  return contains ? unique : unique.concat(node)
}, [])

// Get names for all unique identifiers.
var names = map(uniqueIdentifiers, function(node) { return node.name })

// Find all the global identifiers
var globals = filter(ast, function(node) {
  var path = node.parent
  // That's an exercise to you my friend, but hopefully you got the idea!
  return isGlobal(path)
})

Install

npm install tree-reduce
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