Hi! Given:
def mkParam(p: Param): Term.Param = q"${p.value}: String"and
for {
…
params = matched.params.map(mkParam)
} yield q"def $name($params): Response = client.$method($path)"I run into two issues:
error: type mismatch;
found : meta.Term.Ascribe
required: scala.meta.Term.Param
def mkParam(p: Param): Term.Param = q"${p.value}: String"
^and
error: type mismatch when unquoting;
found : List[scala.meta.Term.Param]
required: scala.meta.Term.Param
} yield q"def $name($params): Response = client.$method($path)"
^I did not find documentation about how to construct interpolated quasi quote strings to create parameter lists for def and how to create Parameters in general. How do I do this and/or where in the documentation is this?
what happens if you do
param"${p.value}: String" instead of q"${p.value}: String"?
thanks! That leaves me with the other problem, still
error: type mismatch when unquoting;
found : List[scala.meta.Term.Param]
required: scala.meta.Term.Param
} yield q"def $name($params): Response = client.$method($path)"
^
@ val params = List(param"a: Int", param"b: String")
params: List[Term.Param] = List(
Term.Param(List(), Term.Name("a"), Some(Type.Name("Int")), None),
Term.Param(List(), Term.Name("b"), Some(Type.Name("String")), None)
)
@ q"def foo(..$params) = a".syntax
res7: String = "def foo(a: Int, b: String) = a"
add
.. before $params
Those references are quite dense
ah, yes, I see it now. Thanks again! Seems that the documentation was meant to be read slightly different than how I browsed it
OK, so, how do I construct a
Term.Name using string interpolation? When I do this, all I get is a Stat
method: Term.Name = q"${someString.toLowerCase}" is what I do
I also, in my neverending wisdom, tried adding <>:
error: type mismatch when unquoting;
found : String
required: scala.meta.Term.Name
method: Term.Name = q"<${someString.toLowerCase}>"to no avail.
error: type mismatch;
found : scala.meta.Stat
required: scala.meta.Term.Name
method: Term.Name = q"${someString.toLowerCase}"
oh, I see it now. The example doesn't actually have a
$ sign. Oh my
Guess I have to create them manually
There are some cases where you can interpolate a string and it's interpreted as a term name
but it's usually simplest to use
Term.Name(String) if you know you need a term name
I gotta say scalameta is really cool and it's fun to use :)
q"a" becomes Term.Name("a")
I added a note in the quasiquote spec about using
Term.Name when interpolation is needed scalameta/scalameta@4e5dabd
@urbanchr the issue appears to be caused by this line in Ammonite where it adds scalameta 4.3.20 to the classpath by default https://github.com/lihaoyi/Ammonite/blob/master/build.sc#L205
There are some obviously non-trivial problems to solve, like how do you treat implicits, etc., but it looks like we're closer to a possibility of having that than back then
hi all, I'm trying to use scalameta for code generation. i have referred documentation multiple times. is there a sample example that covers all the features of how to use it? any help is greatly appreciated, thx! (also on a side not, i have never used macros before. would that be a blocker?)
1 reply
Hey guys, i am just getting the hang of scala meta. I am interested in visiting each tree node and folding it into a new type. Something like a fold method for trees. The closest i have found is the tree traverser but it is restricted to the type Unit. Is there anything like this:
tree.foldLeft[B](z:B)(op: (B,tree) => B):B ? Or some method to simulate this behaviour?
@olafurpg
Transformers apply method override def apply(tree: Tree): Tree is restricted to the type Tree. So i can only transform tree classes into other valid tree classes. But i'd like to transform them into my own type. What i really want is something like having a tree and counting the number of traits inside the tree. So i would want to recursively add 1 on each tree node representing a trait. I think it might be possible using a context class (in the example this would be counter:Int) in a traverser that simulates the accumulator in foldleft. Edit: In the example i want this behaviour: tree.foldleft(0){ (t,i) => if(t equals ("trait")) i + 1 else i }
You can probably implement a purer wrapper around that pattern
I normally write a helper method that wires everything together so that the mutability doesn't leak
def computeFoo(t: Tree): Foo {
val t = new MyFooTraverser()
t.traverse(t)
t.result()
}
Thx for the suggestion! I usually don't like working with mutable fields. As i look through
Trees.scala it could also be possible to actually implement a foldLeft function on the tree nodes that interest me myself. I might give that a try. Maybe it would be worth it considering to implement some kind of generic Visitor Pattern on tree notes ? I like for example the way ANTLR4 makes use of the Visitor Pattern :)
I agree the visitor pattern is a very nice way to build values from a tree traversal. It's not on the roadmap to implement this for scalameta, but I suspect it wouldn't be too hard to implement on top of the
Traverser class similar to how Tree.collect() implements a pure API on top of Traverser
@hugo-vrijswijk @olafurpg i can achieve what i want by using collect . For each node i now first call collect on each child passing a custom operation and then perform the operation on the node itself. This way i can write a custom recursion on the tree. Thx for the suggestion ! It is a bit hacky because at the end i get a List as a result of collect but all i need is a single value return, but it'll do.