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Adjust example and fix showExtractors note on tasty-reflect doc #7039

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Aug 14, 2019
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Adjust example and fix showExtractors note on tasty-reflect doc #7039

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22 changes: 13 additions & 9 deletions docs/docs/reference/metaprogramming/tasty-reflect.md
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Original file line number Diff line number Diff line change
Expand Up @@ -20,8 +20,8 @@ guarantees and may fail at macro expansion time, hence additional explicit
checks must be done.

To provide reflection capabilities in macros we need to add an implicit
parameter of type `scala.quoted.QuoteContext` and import `tasty._` from it in the scope where it
is used.
parameter of type `scala.quoted.QuoteContext` and import `tasty._` from it in
the scope where it is used.

```scala
import scala.quoted._
Expand All @@ -47,18 +47,22 @@ def natConstImpl(x: Expr[Int]) given (qctx: QuoteContext): Expr[Int] = {
import qctx.tasty._
val xTree: Term = x.unseal
xTree match {
case Term.Literal(Constant.Int(n)) =>
if (n <= 0)
QuoteError("Parameter must be natural number")
n.toExpr
case Inlined(_, _, Literal(Constant(n: Int))) =>
if (n <= 0) {
qctx.error("Parameter must be natural number")
'{0}
} else {
xTree.seal.cast[Int]
}
case _ =>
QuoteError("Parameter must be a known constant")
qctx.error("Parameter must be a known constant")
'{0}
}
}
```

To easily know which extractors are needed, the `qctx.tasty.Term.show` method
returns the string representation of the extractors.
To easily know which extractors are needed, the `showExtractors` method on a
`qctx.tasty.Term` returns the string representation of the extractors.

The method `qctx.tasty.Term.seal[T]` provides a way to go back to a
`quoted.Expr[Any]`. Note that the type is `Expr[Any]`. Consequently, the type
Expand Down