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This commit introduces internal attachment that allows unapply macros to be aware of their sub patterns and tweak their expansion depending on that info. At the moment this is not possible due to the way pattern macros are expanded: case MacroPat(inner1, inner2) => ... During type checking this will expand as MacroPat.unapply(<unapply-dummy>) Meaning that macro can’t see inner1 and inner2 in it’s macroApplication. To circumvent this we attach that info as an attachment to the dummy.
1. Refactor Holes slice of quasiquotes to make unliftable fit into
the same framework; replace 3 entities: Holes, HoleTypes and Location
with just a single Hole concept (equiv to previous Holes + HoleTypes)
and some matchers over types (equiv to previous Locations);
2. Move Liftable trait inside of the cake; this is crucial to decrease
boilerplate that is required to define liftable and to allow
combining of liftables together with unliftables in the same class
without pulling ones hair out;
3. Introduce Unliftable — a type class similar to liftable that lets
users to extract custom data types out of trees with the help of
straightforward type ascription syntax:
val q“foo.bar(${baz: Baz})” = ...
This will use Unliftable[Baz] to extract custom data type Baz out of
a tree nested inside of the another tree. A simpler example would be
extracting of constant values:
val q”${x: Int} + ${y: Int}” = q”1 + 2”
4. Vastly increase number of standard liftables.
Contributor
Author
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I've found a corner case that needs some more work |
Contributor
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I'm never on the cutting edge of anything, but I already have a commented on SO where I had nothing new to add. |
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This pr introduces a new
Unliftabletype class used by quasiquotes to extract custom data types out of trees:When an implicit value of Unliftable[T] is provided this means that user can extract value of T inside of the quasiquote pattern:
Where this code is semantically equivalent to:
The major use-case for introduction of
Unliftableis vast simplification of extraction of leaf values from the trees:Previously users had to resort to nesting manual tree subpatterns to extract such values:
review by @retronym and @xeno-by