/* NSC -- new Scala compiler
* Copyright 2005-2006 LAMP/EPFL
* @author Martin Odersky
*/
// $Id$
package scala.tools.nsc.typechecker
import scala.collection.mutable.ListBuffer
import symtab.Flags._
/** This trait ...
*
* @author Martin Odersky
* @version 1.0
*/
trait EtaExpansion requires Analyzer {
import global._
import posAssigner.atPos
/** Expand partial function applications of type `type'.
*
* p.f(es_1)...(es_n)
* ==> {
* private synthetic val eta$f = p.f // if p is not stable
* ...
* private synthetic val eta$e_i = e_i // if e_i is not stable
* ...
*
* (ps_1 => ... => ps_m => eta$f([es_1])...([es_m])(ps_1)...(ps_m))
* }
* tree is already attributed
*/
def etaExpand(tree: Tree): Tree = {
val tpe = tree.tpe
var cnt = 0
def freshName() = { cnt = cnt + 1; newTermName("eta$" + cnt) }
val defs = new ListBuffer[Tree]
/** Append to `defs' value definitions for all non-stable subexpressions
* of the function application <code>tree</code>
*
* @param tree ...
* @return ...
*/
def liftoutPrefix(tree: Tree): Tree = {
def liftout(tree: Tree): Tree =
if (treeInfo.isPureExpr(tree)) tree
else {
val vname: Name = freshName()
defs += atPos(tree.pos)(ValDef(Modifiers(SYNTHETIC), vname, TypeTree(), tree))
Ident(vname) setPos tree.pos
}
tree match {
case Apply(fn, args) =>
copy.Apply(tree, liftoutPrefix(fn), List.mapConserve(args)(liftout)) setType null
case TypeApply(fn, args) =>
copy.TypeApply(tree, liftoutPrefix(fn), args) setType null
case Select(qual, name) =>
copy.Select(tree, liftout(qual), name) setSymbol NoSymbol setType null
case Ident(name) =>
tree
}
}
/** Eta-expand lifted tree.
*
* @param tree ...
* @param tpe ...
* @return ...
*/
def expand(tree: Tree, tpe: Type): Tree = tpe match {
case mt: ImplicitMethodType =>
tree
case MethodType(formals, restpe) =>
val params = formals map (formal =>
ValDef(Modifiers(SYNTHETIC | PARAM), freshName(), TypeTree()
.setType(formal), EmptyTree))
val args = params map (param => Ident(param.name))
atPos(tree.pos)(Function(params, expand(Apply(tree, args), restpe)))
case _ =>
tree
}
val tree1 = liftoutPrefix(tree)
atPos(tree.pos)(Block(defs.toList, expand(tree1, tpe)))
}
}