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Standard library for the Scala Programming Language
/* __ *\
** ________ ___ / / ___ 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}
}
}