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Allow pattern matching anonymous functions of arity > 1 #887

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Merged
merged 4 commits into from
Nov 2, 2015
Merged

Allow pattern matching anonymous functions of arity > 1 #887

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f0e54c5
Allow pattern matching anonymous functions of arity > 1
odersky Oct 30, 2015
2a4d7bc
Fix case expansion for nullary functions.
odersky Oct 30, 2015
9fbb9c9
Revert nullary function patch
odersky Oct 30, 2015
b80b179
Also handle SAM functions when adaptiing arity of case lambdas.
odersky Oct 30, 2015
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16 changes: 11 additions & 5 deletions src/dotty/tools/dotc/ast/Desugar.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -556,14 +556,20 @@ object desugar {
DefDef(nme.ANON_FUN, Nil, params :: Nil, tpt, body).withMods(synthetic),
Closure(Nil, Ident(nme.ANON_FUN), EmptyTree))

/** Expand partial function
/** If `nparams` == 1, expand partial function
*
* { cases }
* ==>
* x$0 => x$0 match { cases }
* x$1 => x$1 match { cases }
*
* If `nparams` > 1, expand instead to
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scalac also allows pattern matching anonymous functions with an expected type of Function0:

% cat sandbox/test.scala
class Test {
  ({case _ if "".isEmpty => 0} : (() => Any)).apply()
}

%  qscalac -Xprint:typer sandbox/test.scala
[[syntax trees at end of                     typer]] // test.scala
package <empty> {
  class Test extends scala.AnyRef {
    def <init>(): Test = {
      Test.super.<init>();
      ()
    };
    ((() => () match {
  case _ if "".isEmpty() => 0
}): () => Any).apply()
  }
}

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That might fall out of this implementation too, but the doc needs an update.

*
* (x$1, ..., x$n) => (x$0, ..., x${n-1}) match { cases }
*/
def makeCaseLambda(cases: List[CaseDef])(implicit ctx: Context) = {
val param = makeSyntheticParameter()
Function(param :: Nil, Match(Ident(param.name), cases))
def makeCaseLambda(cases: List[CaseDef], nparams: Int = 1)(implicit ctx: Context) = {
val params = (1 to (nparams min 1)).toList.map(makeSyntheticParameter(_))
val selector = makeTuple(params.map(p => Ident(p.name)))
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Probably need to report an error if n > MaxTupleArity, which might result from a SAM method type.

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@retronym We don't intend to keep MaxTupleArity for much longer anyway.

Function(params, Match(selector, cases))
}

/** Add annotation with class `cls` to tree:
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6 changes: 5 additions & 1 deletion src/dotty/tools/dotc/typer/Typer.scala
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Expand Up @@ -629,7 +629,11 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
def typedMatch(tree: untpd.Match, pt: Type)(implicit ctx: Context) = track("typedMatch") {
tree.selector match {
case EmptyTree =>
typed(desugar.makeCaseLambda(tree.cases) withPos tree.pos, pt)
val arity = pt match {
case defn.FunctionType(args, _) => args.length
case _ => 1
}
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Recent versions of scalac (2.10+?) are more lenient, the expected type of a patmat anon function need only have a FunctionN with fully defined argument types as base type.

class Test {
  trait X extends Function1[Int, String]
  implicit def f2x(f: Function1[Int, String]): X = ???
  ({case _ if "".isEmpty => ""} : X) // allowed, implicit view used to adapt

  ({case _ if "".isEmpty => 0} : X) // expected String, found Int
}

This change was motivated by spores.

http://issues.scala-lang.org/browse/SI-6221

typed(desugar.makeCaseLambda(tree.cases, arity) withPos tree.pos, pt)
case _ =>
val sel1 = typedExpr(tree.selector)
val selType = widenForMatchSelector(
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4 changes: 4 additions & 0 deletions tests/pos/i873.scala
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@@ -0,0 +1,4 @@
object Test {
def call(k: (Int, Int) => Unit): Unit = ???
def test = call({ case (x, y) => ()})
}