/* NSC -- new Scala compiler * Copyright 2005-2013 LAMP/EPFL * @author Martin Odersky */ package scala.tools.nsc package typechecker import scala.collection.mutable.ListBuffer import symtab.Flags._ /** This trait ... * * @author Martin Odersky * @version 1.0 */ trait EtaExpansion { self: Analyzer => import global._ object etaExpansion { private def isMatch(vparam: ValDef, arg: Tree) = arg match { case Ident(name) => vparam.name == name case _ => false } def unapply(tree: Tree): Option[(List[ValDef], Tree, List[Tree])] = tree match { case Function(vparams, Apply(fn, args)) if (vparams corresponds args)(isMatch) => Some((vparams, fn, args)) case _ => None } } /**
* 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$f([es_1])...([es_m])(ps_1)...(ps_m)) * }*
* tree is already attributed *
*/ def etaExpand(unit : CompilationUnit, tree: Tree, typer: Typer): Tree = { val tpe = tree.tpe var cnt = 0 // for NoPosition def freshName() = { cnt += 1 unit.freshTermName("eta$" + (cnt - 1) + "$") } val defs = new ListBuffer[Tree] /** Append todefs
value definitions for all non-stable
* subexpressions of the function application tree
.
*
* @param tree ...
* @return ...
*/
def liftoutPrefix(tree: Tree): Tree = {
def liftout(tree: Tree, byName: Boolean): Tree =
if (treeInfo.isExprSafeToInline(tree)) tree
else {
val vname: Name = freshName()
// Problem with ticket #2351 here
defs += atPos(tree.pos) {
val rhs = if (byName) {
val res = typer.typed(Function(List(), tree))
new ChangeOwnerTraverser(typer.context.owner, res.symbol) traverse tree // SI-6274
res
} else tree
ValDef(Modifiers(SYNTHETIC), vname.toTermName, TypeTree(), rhs)
}
atPos(tree.pos.focus) {
if (byName) Apply(Ident(vname), List()) else Ident(vname)
}
}
val tree1 = tree match {
// a partial application using named arguments has the following form:
// { val qual$1 = qual
// val x$1 = arg1
// [...]
// val x$n = argn
// qual$1.fun(x$1, ..)..(.., x$n) }
// Eta-expansion has to be performed on `fun`
case Block(stats, fun) =>
defs ++= stats
liftoutPrefix(fun)
case Apply(fn, args) =>
val byName: Int => Option[Boolean] = fn.tpe.params.map(p => definitions.isByNameParamType(p.tpe)).lift
val newArgs = mapWithIndex(args) { (arg, i) =>
// with repeated params, there might be more or fewer args than params
liftout(arg, byName(i).getOrElse(false))
}
treeCopy.Apply(tree, liftoutPrefix(fn), newArgs) setType null
case TypeApply(fn, args) =>
treeCopy.TypeApply(tree, liftoutPrefix(fn), args) setType null
case Select(qual, name) =>
treeCopy.Select(tree, liftout(qual, false), name) setSymbol NoSymbol setType null
case Ident(name) =>
tree
}
if (tree1 ne tree) tree1 setPos tree1.pos.makeTransparent
tree1
}
/** Eta-expand lifted tree.
*/
def expand(tree: Tree, tpe: Type): Tree = tpe match {
case mt @ MethodType(paramSyms, restpe) if !mt.isImplicit =>
val params: List[(ValDef, Boolean)] = paramSyms.map {
sym =>
val origTpe = sym.tpe
val isRepeated = definitions.isRepeatedParamType(origTpe)
// SI-4176 Don't leak A* in eta-expanded function types. See t4176b.scala
val droppedStarTpe = if (settings.etaExpandKeepsStar.value) origTpe else dropRepeatedParamType(origTpe)
val valDef = ValDef(Modifiers(SYNTHETIC | PARAM), sym.name.toTermName, TypeTree(droppedStarTpe), EmptyTree)
(valDef, isRepeated)
}
atPos(tree.pos.makeTransparent) {
val args = params.map {
case (valDef, isRepeated) => gen.paramToArg(Ident(valDef.name), isRepeated)
}
Function(params.map(_._1), expand(Apply(tree, args), restpe))
}
case _ =>
tree
}
val tree1 = liftoutPrefix(tree)
atPos(tree.pos)(Block(defs.toList, expand(tree1, tpe)))
}
}