text: 
  // Walk through the file-system "database" of installed
  // packages, and create a data object related to the
  // installed versions of each package.
  
  /*
  This will traverse through all node_modules folders,
  resolving the dependencies object to the object corresponding to
  the package that meets that dep, or just the version/range if
  unmet.
  
  Assuming that you had this folder structure:
  
  /path/to
  +-- package.json { name = "root" }
  `-- node_modules
      +-- foo {bar, baz, asdf}
      | +-- node_modules
      |   +-- bar { baz }
      |   `-- baz
      `-- asdf
  
  where "foo" depends on bar, baz, and asdf, bar depends on baz,
  and bar and baz are bundled with foo, whereas "asdf" is at
  the higher level (sibling to foo), you'd get this object structure:
  
  { <package.json data>
  , path: "/path/to"
  , parent: null
  , dependencies:
    { foo :
      { version: "1.2.3"
      , path: "/path/to/node_modules/foo"
      , parent: <Circular: root>
      , dependencies:
        { bar:
          { parent: <Circular: foo>
          , path: "/path/to/node_modules/foo/node_modules/bar"
          , version: "2.3.4"
          , dependencies: { baz: <Circular: foo.dependencies.baz> }
          }
        , baz: { ... }
        , asdf: <Circular: asdf>
        }
      }
    , asdf: { ... }
    }
  }
  
  Unmet deps are left as strings.
  Extraneous deps are marked with extraneous:true
  deps that don't meet a requirement are marked with invalid:true
  
  to READ(packagefolder, parentobj, name, reqver)
  obj = read package.json
  installed = ./node_modules/*
  if parentobj is null, and no package.json
    obj = {dependencies:{<installed>:"*"}}
  deps = Object.keys(obj.dependencies)
  obj.path = packagefolder
  obj.parent = parentobj
  if name, && obj.name !== name, obj.invalid = true
  if reqver, && obj.version !satisfies reqver, obj.invalid = true
  if !reqver && parentobj, obj.extraneous = true
  for each folder in installed
    obj.dependencies[folder] = READ(packagefolder+node_modules+folder,
                                    obj, folder, obj.dependencies[folder])
  # walk tree to find unmet deps
  for each dep in obj.dependencies not in installed
    r = obj.parent
    while r
      if r.dependencies[dep]
        if r.dependencies[dep].verion !satisfies obj.dependencies[dep]
          WARN
          r.dependencies[dep].invalid = true
        obj.dependencies[dep] = r.dependencies[dep]
        r = null
      else r = r.parent
  return obj
  
  
  TODO:
  1. Find unmet deps in parent directories, searching as node does up
  as far as the left-most node_modules folder.
  2. Ignore anything in node_modules that isn't a package folder.
  
  */
  
  try {
    var fs = require("graceful-fs")
  } catch (er) {
    var fs = require("fs")
  }
  
  try {
    var log = require("npmlog")
  } catch (_) {
    var log = { verbose: noop, info: noop, warn: noop, error: noop }
    function noop () {}
  }
  
  var path = require("path")
  var asyncMap = require("slide").asyncMap
  var semver = require("semver")
  var readJson = require("read-package-json")
  var url = require("url")
  
  module.exports = readInstalled
  
  function readInstalled (folder, depth, cb) {
    if (typeof cb !== "function") cb = depth, depth = Infinity
    readInstalled_(folder, null, null, null, 0, depth, function (er, obj) {
      if (er) return cb(er)
      // now obj has all the installed things, where they're installed
      // figure out the inheritance links, now that the object is built.
      resolveInheritance(obj)
      cb(null, obj)
    })
  }
  
  var rpSeen = {}
  function readInstalled_ (folder, parent, name, reqver, depth, maxDepth, cb) {
    //console.error(folder, name)
  
    var installed
      , obj
      , real
      , link
  
    fs.readdir(path.resolve(folder, "node_modules"), function (er, i) {
      // error indicates that nothing is installed here
      if (er) i = []
      installed = i.filter(function (f) { return f.charAt(0) !== "." })
      next()
    })
  
    readJson(path.resolve(folder, "package.json"), function (er, data) {
      obj = copy(data)
  
      if (!parent) {
        obj = obj || true
        er = null
      }
      return next(er)
    })
  
    fs.lstat(folder, function (er, st) {
      if (er) {
        if (!parent) real = true
        return next(er)
      }
      fs.realpath(folder, function (er, rp) {
        //console.error("realpath(%j) = %j", folder, rp)
        real = rp
        if (st.isSymbolicLink()) link = rp
        next(er)
      })
    })
  
    var errState = null
      , called = false
    function next (er) {
      if (errState) return
      if (er) {
        errState = er
        return cb(null, [])
      }
      //console.error('next', installed, obj && typeof obj, name, real)
      if (!installed || !obj || !real || called) return
      called = true
      if (rpSeen[real]) return cb(null, rpSeen[real])
      if (obj === true) {
        obj = {dependencies:{}, path:folder}
        installed.forEach(function (i) { obj.dependencies[i] = "*" })
      }
      if (name && obj.name !== name) obj.invalid = true
      obj.realName = name || obj.name
      obj.dependencies = obj.dependencies || {}
  
      // "foo":"http://blah" is always presumed valid
      if (reqver
          && semver.validRange(reqver)
          && !semver.satisfies(obj.version, reqver)) {
        obj.invalid = true
      }
  
      if (parent
          && !(name in parent.dependencies)
          && !(name in (parent.devDependencies || {}))) {
        obj.extraneous = true
      }
      obj.path = obj.path || folder
      obj.realPath = real
      obj.link = link
      if (parent && !obj.link) obj.parent = parent
      rpSeen[real] = obj
      obj.depth = depth
      //if (depth >= maxDepth) return cb(null, obj)
      asyncMap(installed, function (pkg, cb) {
        var rv = obj.dependencies[pkg]
        if (!rv && obj.devDependencies) rv = obj.devDependencies[pkg]
        if (depth >= maxDepth) {
          // just try to get the version number
          var pkgfolder = path.resolve(folder, "node_modules", pkg)
            , jsonFile = path.resolve(pkgfolder, "package.json")
          return readJson(jsonFile, function (er, depData) {
            // already out of our depth, ignore errors
            if (er || !depData || !depData.version) return cb(null, obj)
            obj.dependencies[pkg] = depData.version
            cb(null, obj)
          })
        }
  
        readInstalled_( path.resolve(folder, "node_modules/"+pkg)
                      , obj, pkg, obj.dependencies[pkg], depth + 1, maxDepth
                      , cb )
  
      }, function (er, installedData) {
        if (er) return cb(er)
        installedData.forEach(function (dep) {
          obj.dependencies[dep.realName] = dep
        })
  
        // any strings here are unmet things.  however, if it's
        // optional, then that's fine, so just delete it.
        if (obj.optionalDependencies) {
          Object.keys(obj.optionalDependencies).forEach(function (dep) {
            if (typeof obj.dependencies[dep] === "string") {
              delete obj.dependencies[dep]
            }
          })
        }
        return cb(null, obj)
      })
    }
  }
  
  // starting from a root object, call findUnmet on each layer of children
  var riSeen = []
  function resolveInheritance (obj) {
    if (typeof obj !== "object") return
    if (riSeen.indexOf(obj) !== -1) return
    riSeen.push(obj)
    if (typeof obj.dependencies !== "object") {
      obj.dependencies = {}
    }
    Object.keys(obj.dependencies).forEach(function (dep) {
      findUnmet(obj.dependencies[dep])
    })
    Object.keys(obj.dependencies).forEach(function (dep) {
      resolveInheritance(obj.dependencies[dep])
    })
  }
  
  // find unmet deps by walking up the tree object.
  // No I/O
  var fuSeen = []
  function findUnmet (obj) {
    if (fuSeen.indexOf(obj) !== -1) return
    fuSeen.push(obj)
    //console.error("find unmet", obj.name, obj.parent && obj.parent.name)
    var deps = obj.dependencies = obj.dependencies || {}
    //console.error(deps)
    Object.keys(deps)
      .filter(function (d) { return typeof deps[d] === "string" })
      .forEach(function (d) {
        //console.error("find unmet", obj.name, d, deps[d])
        var r = obj.parent
          , found = null
        while (r && !found && typeof deps[d] === "string") {
          // if r is a valid choice, then use that.
          found = r.dependencies[d]
          if (!found && r.realName === d) found = r
  
          if (!found) {
            r = r.link ? null : r.parent
            continue
          }
          if ( typeof deps[d] === "string"
              // url deps presumed innocent.
              && !url.parse(deps[d]).protocol
              && !semver.satisfies(found.version, deps[d])) {
            // the bad thing will happen
            log.warn("unmet dependency", obj.path + " requires "+d+"@'"+deps[d]
                    +"' but will load\n"
                    +found.path+",\nwhich is version "+found.version
                    )
            found.invalid = true
          }
          deps[d] = found
        }
  
      })
    log.verbose("readInstalled", "returning", obj._id)
    return obj
  }
  
  function copy (obj) {
    if (!obj || typeof obj !== 'object') return obj
    if (Array.isArray(obj)) return obj.map(copy)
  
    var o = {}
    for (var i in obj) o[i] = copy(obj[i])
    return o
  }
  