Skip to content
This repository
Fetching contributors…

Octocat-spinner-32-eaf2f5

Cannot retrieve contributors at this time

file 348 lines (295 sloc) 16.572 kb
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2006-2013, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */

package scala.util.parsing.ast

import scala.collection.AbstractIterable
import scala.collection.mutable
import scala.language.implicitConversions

//DISCLAIMER: this code is highly experimental!

  // TODO: avoid clashes when substituting
  // TODO: check binders in the same scope are distinct

/** This trait provides the core ''Scrap-Your-Boilerplate'' abstractions as
* well as implementations for common datatypes.
*
* (Based on Ralf Lämmel's [[http://homepages.cwi.nl/~ralf/syb3/ SYB papers]].)
*
* @author Adriaan Moors
*/
@deprecated("This class will be removed", "2.10.0")
trait Mappable {
  trait Mapper { def apply[T <% Mappable[T]](x: T): T } /* TODO: having type `Forall T. T => T` is too strict:
sometimes we want to allow `Forall T >: precision. T => T` for some type `precision`, so that,
beneath a certain threshold, we have some leeway.
concretely: to use gmap for substitution, we simply require that ast nodes are mapped to ast nodes,
we can't require that the type is preserved precisely: a Name may map to e.g., a MethodCall
*/

  trait Mappable[T] {
    // one-layer traversal
    def gmap(f: Mapper): T
    // everywhere f x = f (gmapT (everywhere f) x)
    def everywhere(f: Mapper)(implicit c: T => Mappable[T]): T =
      f(gmap(new Mapper { def apply[T <% Mappable[T]](x: T): T = x.everywhere(f)}))
  }

  implicit def StringIsMappable(s: String): Mappable[String] =
    new Mappable[String] {
      def gmap(f: Mapper): String = f(s)
    }

  implicit def ListIsMappable[t <% Mappable[t]](xs: List[t]): Mappable[List[t]] =
    new Mappable[List[t]] {
      def gmap(f: Mapper): List[t] = (for (x <- xs) yield f(x)).toList
    }

  implicit def OptionIsMappable[t <% Mappable[t]](xs: Option[t]): Mappable[Option[t]] =
    new Mappable[Option[t]] {
      def gmap(f: Mapper): Option[t] = (for (x <- xs) yield f(x))
    }
}

/** This component provides functionality for enforcing variable binding
* during parse-time.
*
* When parsing simple languages, like Featherweight Scala, these parser
* combinators will fully enforce the binding discipline. When names are
* allowed to be left unqualified, these mechanisms would have to be
* complemented by an extra phase that resolves names that couldn't be
* resolved using the naive binding rules. (Maybe some machinery to
* model `implicit` binders (e.g., `this` and imported qualifiers)
* and selection on a binder will suffice?)
*
* @author Adriaan Moors
*/
trait Binders extends AbstractSyntax with Mappable {
  /** A `Scope` keeps track of one or more syntactic elements that represent bound names.
* The elements it contains share the same scope and must all be distinct, as determined by `==`.
*
* A `NameElement` `n` in the AST that is conceptually bound by a `Scope` `s`, is replaced by a
* `BoundElement(n, s)`. (For example, in `val x:Int=x+1`, the first `x` is modelled by a
* Scope `s` that contains `x` and the second `x` is represented by a `BoundElement(x, s)`)
* The term (`x+1`) in scope of the Scope becomes an `UnderBinder(s, x+1)`.
*
* A `NameElement` `n` is bound by a `Scope` `s` if it is wrapped as a `BoundElement(n, s)`, and
* `s` has a binder element that is semantically equal (`equals` or `==`) to `n`.
*
* A `Scope` is represented textually by its list of binder elements, followed by the scope's `id`.
* For example: `[x, y]!1` represents the scope with `id` `1` and binder elements `x` and `y`.
* (`id` is solely used for this textual representation.)
*/
  class Scope[binderType <: NameElement] extends AbstractIterable[binderType] with Iterable[binderType] {
    private val substitution: mutable.Map[binderType, Element] =
      new mutable.LinkedHashMap[binderType, Element] // a LinkedHashMap is ordered by insertion order -- important!

    /** Returns a unique number identifying this Scope (only used for representation purposes). */
    val id: Int = _Binder.genId

    /** Returns the binders in this scope.
* For a typical let-binding, this is just the variable name. For an argument list to a method body,
* there is one binder per formal argument.
*/
    def iterator = substitution.keysIterator

    /** Return the `i`th binder in this scope. */
    def apply(i: Int): binderType = this.iterator.toList(i)

    /** Returns true if this container has a binder equal (as determined by `==`) to `b`. */
    def binds(b: binderType): Boolean = substitution.contains(b)

    def indexFor(b: binderType): Option[Int] = {
      val iter = this.iterator.zipWithIndex
      for ((that, count) <- iter) {
        if (that.name == b.name) // TODO: why do name equals and structural equals differ?
          return Some(count + 1)
        else
          Console.println(that+"!="+b)
      }

      None
    }

    /** Adds a new binder, for example the variable name in a local variable declaration.
*
* @param b a new binder that is distinct from the existing binders in this scope,
* and shares their conceptual scope. `canAddBinder(b)` must hold.
* @return `binds(b)` and `getElementFor(b) eq b` will hold.
*/
    def addBinder(b: binderType) { substitution += Pair(b, b) }

    // TODO: strengthen this condition so that no binders may be added after this scope has been
    // linked to its `UnderBinder` (i.e., while parsing, BoundElements may be added to the Scope
    // associated to the UnderBinder, but after that, no changes are allowed, except for substitution)?
    /** `canAddElement` indicates whether `b` may be added to this scope.
*
*
* @return true if `b` had not been added yet
*/
    def canAddBinder(b: binderType): Boolean = !binds(b)

    /** ''Replaces'' the bound occurrences of a contained binder by their new value.
* The bound occurrences of `b` are not actually replaced; the scope keeps track
* of a substitution that maps every binder to its current value. Since a `BoundElement` is
* a proxy for the element it is bound to by its binder, `substitute` may thus be thought of
* as replacing all the bound occurrences of the given binder `b` by their new value `value`.
*
* @param b the binder whose bound occurrences should be given a new value. `binds(b)` must hold.
* @param value the new value for the bound occurrences of `b`
* @return `getElementFor(b) eq value` will hold.
*/
    def substitute(b: binderType, value: Element): Unit = substitution(b) = value

    /** Returns the current value for the bound occurrences of `b`.
*
* @param b the contained binder whose current value should be returned `binds(b)` must hold.
*/
    def getElementFor(b: binderType): Element = substitution(b)

    override def toString: String = this.iterator.toList.mkString("[",", ","]")+"!"+id // TODO show substitution?

    /** Returns a list of strings that represent the binder elements, each tagged with this scope's id. */
    def bindersToString: List[String] = (for(b <- this.iterator) yield b+"!"+id).toList

    /** Return a new inheriting scope that won't check whether binding is respected until the scope is left (so as to support forward references). */
    def allowForwardRef: Scope[binderType] = this // TODO

    /** Return a nested scope -- binders entered into it won't be visible in this scope, but if this scope allows forward references,
* the binding in the returned scope also does, and thus the check that all variables are bound is deferred until this scope is left.
*/
    def nested: Scope[binderType] = this // TODO

    def onEnter() {}
    def onLeft() {}
  }


  trait BindingSensitive {
    // would like to specify this as one method:
    // def alpha_==[t <: NameElement](other: BoundElement[t]): Boolean
    // def alpha_==[bt <: binderType, st <: elementT](other: UnderBinder[bt, st]): Boolean
  }

  /** A `BoundElement` is bound in a certain scope `scope`, which keeps track of the actual element that
* `el` stands for.
*
* A `BoundElement` is represented textually by its bound element, followed by its scope's `id`.
* For example: `x@1` represents the variable `x` that is bound in the scope with `id` `1`.
*
* @note `scope.binds(el)` holds before and after.
*/
  case class BoundElement[boundElement <: NameElement](el: boundElement, scope: Scope[boundElement]) extends NameElement with Proxy with BindingSensitive {
    /** Returns the element this `BoundElement` stands for.
* The `Proxy` trait ensures `equals`, `hashCode` and `toString` are forwarded to
* the result of this method.
*/
    def self: Element = scope.getElementFor(el)

    def name = self.asInstanceOf[NameElement].name // TODO: this is only safe when substituted to a NameElement, which certainly isn't required -- I want dynamic inheritance! :)

    // decorate element's representation with the id of the scope it's bound in
    override def toString: String = super.toString+"@"+scope.id

    def alpha_==[t <: NameElement](other: BoundElement[t]): Boolean = scope.indexFor(el) == other.scope.indexFor(other.el)
  }

  /** A variable that escaped its scope (i.e., a free variable) -- we don't deal very well with these yet. */
  class UnboundElement[N <: NameElement](private val el: N) extends NameElement {
    def name = el.name+"@??"
  }

  // this is useless, as Element is a supertype of BoundElement --> the coercion will never be inferred
  // if we knew a more specific type for the element that the bound element represents, this could make sense
  // implicit def BoundElementProxy[t <: NameElement](e: BoundElement[t]): Element = e.self

  /** Represents an element with variables that are bound in a certain scope. */
  class UnderBinder[binderType <: NameElement, elementT <% Mappable[elementT]](val scope: Scope[binderType], private[Binders] val element: elementT) extends Element with BindingSensitive {
    override def toString: String = "(" + scope.toString + ") in { "+element.toString+" }"

    /** Alpha-equivalence -- TODO
* Returns true if the `element` of the `other` `UnderBinder` is equal to this `element` up to alpha-conversion.
*
* That is, regular equality is used for all elements but `BoundElement`s: such an element is
* equal to a `BoundElement` in `other` if their binders are equal. Binders are equal if they
* are at the same index in their respective scope.
*
* Example:
* {{{
* UnderBinder([x, y]!1, x@1) alpha_== UnderBinder([a, b]!2, a@2)
* ! (UnderBinder([x, y]!1, y@1) alpha_== UnderBinder([a, b]!2, a@2))
* }}}
*/
    /*def alpha_==[bt <: binderType, st <: elementT](other: UnderBinder[bt, st]): Boolean = {
var result = true

// TODO: generic zip or gmap2
element.gmap2(other.element, new Mapper2 {
def apply[s <% Mappable[s], t <% Mappable[t]](x :{s, t}): {s, t} = x match {
case {be1: BoundElement[_], be2: BoundElement[_]} => result == result && be1.alpha_==(be2) // monadic gmap (cheating using state directly)
case {ub1: UnderBinder[_, _], ub2: UnderBinder[_, _]} => result == result && be1.alpha_==(be2)
case {a, b} => result == result && a.equals(b)
}; x
})
}*/

    def cloneElementWithSubst(subst: Map[NameElement, NameElement]) = element.gmap(new Mapper { def apply[t <% Mappable[t]](x :t): t = x match{
      case substable: NameElement if subst.contains(substable) => subst.get(substable).asInstanceOf[t] // TODO: wrong... substitution is not (necessarily) the identity function
         //Console.println("substed: "+substable+"-> "+subst.get(substable)+")");
      case x => x // Console.println("subst: "+x+"(keys: "+subst.keys+")");x
    }})

    // TODO
    def cloneElementNoBoundElements = element.gmap(new Mapper { def apply[t <% Mappable[t]](x :t): t = x match{
      case BoundElement(el, _) => new UnboundElement(el).asInstanceOf[t] // TODO: precision stuff
      case x => x
    }})

    def extract: elementT = cloneElementNoBoundElements
    def extract(subst: Map[NameElement, NameElement]): elementT = cloneElementWithSubst(subst)

    /** Get a string representation of element, normally we don't allow direct access to element, but just getting a string representation is ok. */
    def elementToString: String = element.toString
  }

  //SYB type class instances
  implicit def UnderBinderIsMappable[bt <: NameElement <% Mappable[bt], st <% Mappable[st]](ub: UnderBinder[bt, st]): Mappable[UnderBinder[bt, st]] =
    new Mappable[UnderBinder[bt, st]] {
      def gmap(f: Mapper): UnderBinder[bt, st] = UnderBinder(f(ub.scope), f(ub.element))
    }

  implicit def ScopeIsMappable[bt <: NameElement <% Mappable[bt]](scope: Scope[bt]): Mappable[Scope[bt]] =
    new Mappable[Scope[bt]] {
      def gmap(f: Mapper): Scope[bt] = { val newScope = new Scope[bt]()
        for(b <- scope) newScope.addBinder(f(b))
        newScope
      }
    }

  implicit def NameElementIsMappable(self: NameElement): Mappable[NameElement] = new Mappable[NameElement] {
    def gmap(f: Mapper): NameElement = self match {
      case BoundElement(el, scope) => BoundElement(f(el), f(scope))
      case _ => UserNameElementIsMappable(self).gmap(f)
    }
  }

  def UserNameElementIsMappable[t <: NameElement](self: t): Mappable[t]

  object UnderBinder {
    def apply[binderType <: NameElement, elementT <% Mappable[elementT]](scope: Scope[binderType], element: elementT) = new UnderBinder(scope, element)
    def unit[bt <: NameElement, elementT <% Mappable[elementT]](x: elementT) = UnderBinder(new Scope[bt](), x)
  }

  /** If a list of `UnderBinder`s all have the same scope, they can be turned in to an `UnderBinder`
* containing a list of the elements in the original `UnderBinder`.
*
* The name `sequence` comes from the fact that this method's type is equal to the type of monadic sequence.
*
* @note `!orig.isEmpty` implies `orig.forall(ub => ub.scope eq orig(0).scope)`
*
*/
  def sequence[bt <: NameElement, st <% Mappable[st]](orig: List[UnderBinder[bt, st]]): UnderBinder[bt, List[st]] =
    if(orig.isEmpty) UnderBinder.unit(Nil)
    else UnderBinder(orig(0).scope, orig.map(_.element))

  // couldn't come up with a better name...
  def unsequence[bt <: NameElement, st <% Mappable[st]](orig: UnderBinder[bt, List[st]]): List[UnderBinder[bt, st]] =
    orig.element.map(sc => UnderBinder(orig.scope, sc))

  //TODO: more documentation
  /** An environment that maps a `NameElement` to the scope in which it is bound.
* This can be used to model scoping during parsing.
*
* @note This class uses similar techniques as described by ''Burak Emir'' in
* [[http://library.epfl.ch/theses/?nr=3899 Object-oriented pattern matching]],
* but uses `==` instead of `eq`, thus types can't be unified in general.
*/
  abstract class BinderEnv {
    def apply[A <: NameElement](v: A): Option[Scope[A]]
    def extend[a <: NameElement](v : a, x : Scope[a]) = new BinderEnv {
      def apply[b <: NameElement](w : b): Option[Scope[b]] =
        if(w == v) Some(x.asInstanceOf[Scope[b]])
        else BinderEnv.this.apply(w)
    }
  }

  object EmptyBinderEnv extends BinderEnv {
    def apply[A <: NameElement](v: A): Option[Scope[A]] = None
  }

  // TODO: move this to some utility object higher in the scala hierarchy?
  /** Returns a given result, but executes the supplied closure before returning.
* (The effect of this closure does not influence the returned value.)
*/
  trait ReturnAndDo[T]{
    /**
* @param block code to be executed, purely for its side-effects
*/
    def andDo(block: => Unit): T
  }

  def return_[T](result: T): ReturnAndDo[T] =
    new ReturnAndDo[T] {
      val r = result
      def andDo(block: => Unit): T = {block; r}
    }

  private object _Binder {
    private var currentId = 0
    private[Binders] def genId = return_(currentId) andDo {currentId=currentId+1}
  }
}
Something went wrong with that request. Please try again.