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/* NSC -- new Scala compiler
* Copyright 2005-2011 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
}
}
/** <p>
* Expand partial function applications of type <code>type</code>.
* </p><pre>
* p.f(es_1)...(es_n)
* ==> {
* <b>private synthetic val</b> eta$f = p.f // if p is not stable
* ...
* <b>private synthetic val</b> eta$e_i = e_i // if e_i is not stable
* ...
* (ps_1 => ... => ps_m => eta$f([es_1])...([es_m])(ps_1)...(ps_m))
* }</pre>
* <p>
* tree is already attributed
* </p>
*/
def etaExpand(unit : CompilationUnit, tree: Tree): Tree = {
val tpe = tree.tpe
var cnt = 0 // for NoPosition
def freshName() = {
cnt += 1
unit.freshTermName("eta$" + (cnt - 1) + "$")
}
val defs = new ListBuffer[Tree]
/** Append to <code>defs</code> 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()
// Problem with ticket #2351 here
defs += atPos(tree.pos) {
ValDef(Modifiers(SYNTHETIC), vname.toTermName, TypeTree(), tree)
}
Ident(vname) setPos tree.pos.focus
}
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) =>
treeCopy.Apply(tree, liftoutPrefix(fn), args mapConserve (liftout)) setType null
case TypeApply(fn, args) =>
treeCopy.TypeApply(tree, liftoutPrefix(fn), args) setType null
case Select(qual, name) =>
treeCopy.Select(tree, liftout(qual), 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 = paramSyms map (sym =>
ValDef(Modifiers(SYNTHETIC | PARAM),
sym.name.toTermName, TypeTree(sym.tpe) , EmptyTree))
atPos(tree.pos.makeTransparent) {
Function(params, expand(Apply(tree, params map gen.paramToArg), restpe))
}
case _ =>
tree
}
val tree1 = liftoutPrefix(tree)
atPos(tree.pos)(Block(defs.toList, expand(tree1, tpe)))
}
}
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