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author | Denys Shabalin <denys.shabalin@typesafe.com> | 2014-03-24 15:21:32 +0100 |
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committer | Denys Shabalin <denys.shabalin@typesafe.com> | 2014-03-24 15:56:46 +0100 |
commit | fa91b173f7e5e64c2221d50af0684985f046637c (patch) | |
tree | 4ce1ffb4b44edb37aef60cd6e3f93e44460ab146 /src | |
parent | bcf24ec9ba07408ad9e8745135cc941ac3e76289 (diff) | |
download | scala-fa91b173f7e5e64c2221d50af0684985f046637c.tar.gz scala-fa91b173f7e5e64c2221d50af0684985f046637c.tar.bz2 scala-fa91b173f7e5e64c2221d50af0684985f046637c.zip |
SI-8200 provide an identity liftable for trees
This liftable hasn't been originally included in the set of standard
liftables due to following contradiction:
1. On one hand we can have identity lifting that seems to be quite
consistent with regular unquoting:
q"..${List(1,2)}" <==> q"1; 2"
q"${List(1,2)}" <==> q"s.c.i.List(1, 2)"
q"..${List(q"a", q"b")}” <==> q"a; b"
q"${List(q"a", q"b")}" <==> q"s.c.i.List(a, b)"
This is also consistent with how lisp unquoting works although they
get lifting for free thanks to homoiconicity:
// scala
scala> val x = List(q"a", q"b); q"f($x)"
q"f(s.c.i.List(a, b))"
// scheme
> (let [(x (list a b))] `(f ,x))
'(f (list a b))
2. On the other hand lifting is an operation that converts a value into
a code that when evaluated turns into the same value. In this sense
Liftable[Tree] means reification of a tree into a tree that
represents it, i.e.:
q"${List(q"a", q"b")}"
<==>
q"""s.c.i.List(Ident(TermName("a")), Ident(TermName("b")))"""
But I belive that such lifting will be very confusing for everyone
other than a few very advanced users.
This commit introduces the first option as a default Liftable for trees.
Diffstat (limited to 'src')
-rw-r--r-- | src/reflect/scala/reflect/api/StandardLiftables.scala | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/src/reflect/scala/reflect/api/StandardLiftables.scala b/src/reflect/scala/reflect/api/StandardLiftables.scala index af11de46ce..66ac62cc9e 100644 --- a/src/reflect/scala/reflect/api/StandardLiftables.scala +++ b/src/reflect/scala/reflect/api/StandardLiftables.scala @@ -27,6 +27,7 @@ trait StandardLiftables { self: Universe => callScala(stdnme.Symbol)(Literal(Constant(v.name)) :: Nil) } + implicit def liftTree[T <: Tree]: Liftable[T] = Liftable { identity } implicit def liftName[T <: Name]: Liftable[T] = Liftable { name => Ident(name) } implicit def liftExpr[T <: Expr[_]]: Liftable[T] = Liftable { expr => expr.tree } implicit def liftType[T <: Type]: Liftable[T] = Liftable { tpe => TypeTree(tpe) } |