integrating combinators into trunk

2 files changed, 365 insertions, 0 deletions

diff --git a/src/library/scala/util/parsing/ast/AbstractSyntax.scala b/src/library/scala/util/parsing/ast/AbstractSyntax.scala
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+++ b/src/library/scala/util/parsing/ast/AbstractSyntax.scala
@@ -0,0 +1,31 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2006-2007, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |                                         **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+package scala.util.parsing.ast
+
+import scala.util.parsing.input.Positional
+
+/** This component provides the core abstractions for representing an Abstract Syntax Tree
+ *
+ * @author Adriaan Moors
+ */
+trait AbstractSyntax {
+  /** The base class for elements of the abstract syntax tree.
+   */
+  trait Element extends Positional
+
+  /** The base class for elements in the AST that represent names {@see Binders}.
+   */
+  trait NameElement extends Element {
+    def name: String
+    override def equals(that: Any): Boolean = that match {
+      case n: NameElement => n.name == name
+      case _ => false
+    }
+  }
+}
diff --git a/src/library/scala/util/parsing/ast/Binders.scala b/src/library/scala/util/parsing/ast/Binders.scala
new file mode 100644
index 0000000000..4aeb9f40ea
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+++ b/src/library/scala/util/parsing/ast/Binders.scala
@@ -0,0 +1,334 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2006-2007, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |                                         **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+package scala.util.parsing.ast
+
+import scala.collection.mutable.Map
+
+//DISCLAIMER: this code is not well-tested -- consider it beta-quality!
+
+  // 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 Ralph Lämmel's SYB papers
+ *
+ * @author Adriaan Moors
+ */
+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(val 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(val 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 (wrt. ==)
+   *
+   * 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 Iterable[binderType]{
+    private val substitution: Map[binderType, Element] =
+      new scala.collection.jcl.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 elements = substitution.keys
+
+    /** Return the `i'th binder in this scope.*/
+    def apply(i: Int): binderType = elements.toList(i)
+
+    /** Returns true if this container has a binder equal (==) to `b'
+     */
+    def binds(b: binderType): Boolean = substitution.contains(b)
+
+    def indexFor(b: binderType): Option[Int] = {
+      val iter = elements.counted
+      (for(val that <- iter) {
+        if(that.name == b.name) // TODO: why do name equals and structural equals differ?
+          return Some(iter.count)
+        else
+          Console.println(that+"!="+b)
+      })
+
+      None
+    }
+
+    /** Adds a new binder.
+     * (e.g. 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
+     * @pre canAddBinder(b)
+     * @post binds(b)
+     * @post getElementFor(b) eq b
+     */
+    def addBinder(b: binderType) = substitution += b -> b
+
+    /** `canAddElement' indicates whether `b' may be added to this scope.
+     *
+     * 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)?
+     *
+     * @returns 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
+     * @param value the new value for the bound occurrences of `b'
+     * @pre binds(b)
+     * @post getElementFor(b) eq value
+     */
+    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
+		 * @pre binds(b)
+     */
+    def getElementFor(b: binderType): Element = substitution(b)
+
+    override def toString: String =  elements.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(val b <- elements) 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'.
+   *
+   * @invar scope.binds(el)
+   */
+  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: scala.collection.immutable.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: scala.collection.immutable.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(val 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.
+   *
+   * @pre !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))
+
+  /** An environment that maps a `NameElement' to the scope in which it is bound.
+   * This can be used to model scoping during parsing.
+   *
+   * (This class is similar to Burak's ECOOP paper on pattern matching, except that we use `=='
+   *  instead of `eq', thus types can't be unified in general)
+   *
+   * TODO: more documentation
+   */
+  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
+  }
+
+  /** Returns a given result, but executes the supplied closure before returning.
+   * (The effect of this closure does not influence the returned value.)
+   *
+   * TODO: move this to some utility object higher in the scala hierarchy?
+   *
+   * @param result the result to be returned
+   * @param block  code to be executed, purely for its side-effects
+   */
+  trait ReturnAndDo[t]{def andDo(block: =>unit):t} // gotta love Smalltalk syntax :-)
+  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}
+  }
+}