Fix #7788: Add new syntax for conditional given instances #7794
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Treat
given (A, B) => ...
as equivalent to
given A, B => ...
Motivation: Because of the similarity with function types, it's very easy to
wrap multiple types in parentheses by mistake. On the other hand, it
should be extremely rare to demand a tuple of givens. So the syntax tweak
is there to "do what I mean".
bishabosha
requested changes
Dec 18, 2019
| ModuleDef(name, Template(makeConstructor(tparams, vparamss), Nil, Nil, self, stats)) | ||
| else | ||
| checkAllGivens(vparamss, "parameter of given instance") | ||
| def conditionalParents(): List[Tree] = |
There was a problem hiding this comment.
The rules still accept given [A]: (given showA: Show[A]) => Show[List[A]] e.g. :
trait Show[-A] with
def show(a:A): String
given Show[String] = x => x
given Show[Int] = _.toString
given [A,B]: (given sA: Show[A], sB: Show[B]) => Show[(A,B)] = (a,b) => s"(${sA.show(a)}, ${sB.show(b)})"
given [A]: (given Show[A]) => Show[List[A]] = as => as.map(summon[Show[A]].show).mkString(", ")
given showOption[A]: (given Show[A]) => Show[Option[A]] = o => o.map(summon[Show[A]].show).fold("Nothing")(s => s"Some($s)")
given showEither[A,B]: (given sA: Show[A], sb: Show[B]) => Show[Either[A,B]] = _.fold(a => s"Left(${summon[Show[A]].show(a)})", b => s"Right(${summon[Show[B]].show(b)})")
@main def ShowDemo =
println(summon[Show[(Int, String)]].show(0 -> "hello"))
println(summon[Show[List[Int]]].show(List(1,2,3)))
println(summon[Show[Option[Int]]].show(Some(25)))
println(summon[Show[Either[Int, String]]].show(Left(-1)))
println(summon[Show[Either[Int, String]]].show(Right("success message")))There was a problem hiding this comment.
So this syntax is still ok to be alongside the other?
|
|
||
| val isConditional = | ||
| in.token == ARROW | ||
| && vparamss.length == 1 |
There was a problem hiding this comment.
there should probably be a neg test for curried param lists:
trait Show[-A] with
def show(a:A): String
given Show[String] = x => x
given Show[Int] = _.toString
given [A,B]: (sA: Show[A])(sB: Show[B]) => Show[(A,B)] = (a,b) => s"(${sA.show(a)}, ${sB.show(b)})"
given [A,B,C]: (Show[A])(Show[B])(Show[C]) => Show[(A,B,C)] = (a,b,c) => s"(${summon[Show[A]].show(a)}, ${summon[Show[B]].show(b)}, ${summon[Show[C]].show(c)})"
given showEither[A,B]: (sA: Show[A])(sb: Show[B]) => Show[Either[A,B]] = _.fold(a => s"Left(${summon[Show[A]].show(a)})", b => s"Right(${summon[Show[B]].show(b)})")
@main def ShowDemo =
println(summon[Show[(Int, String)]].show(0 -> "hello"))
bishabosha
requested changes
Dec 18, 2019
|
@bishabosha Should be fixed now. I did not include a neg test since the old syntax will probably be dropped anyway. |
bishabosha
requested changes
Dec 18, 2019
Co-Authored-By: Jamie Thompson <[email protected]>
bishabosha
requested changes
Dec 18, 2019
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Trial implementation to experiment with the syntax proposed in #7788.
In the end we will keep only the new or the old way of writing things.