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When you want to point to an asset, you use an AssetRef. This is a refernece specifying how to get to the asset you're looking for. It could be a simple loaded asset, an asset referenced in another asset, or even a subasset (a part of a larger asset).

An AssetRef a can be used with functions such as asset and qasset to attempt to grab the a the ref is pointing to.

Assume you have these two .kdl assets:

assets/foo.kdl

foo {
  f 10
  bar "bars/bar.kdl"
}

assets/bars/bar.kdl

bar {
  b 15
}

And their represenatations in Haskell:

data Foo = Foo {
  f :: Int,
  bar :: AssetRef Bar
}

data Bar = Bar {
  b :: Int
}

To query for the Foo asset, you need to provide an AssetRef Foo, which can be the path to the asset:

foo :: Foo <- asset "foo.kdl"

You can also query directly for the f field of a Foo:

f <- asset $ do
  foo :: Foo <- "foo.kdl"
  pure foo.f

And you can query for the Bar asset referenced by a certain Foo:

bar <- asset $ do
  foo :: Foo <- "foo.kdl"
  foo.bar

Note that this is equivalent to referencing Bar's file directly, assuming you know the path to it:

bar <- asset $ "bars/bar.kdl"

For kdl files in particular, there is an utility called a KdlRef.

Let's rewrite the earlier types, this time with KdlRefs instead of AssetRefs:

data Foo = Foo {
  f :: Int
  bar :: KdlRef Bar
}

data Bar = Bar {
  b :: Int
}

A KdlRef can have two possible values: either a reference to another file, or directly the value of the other asset:

So both of these are valid:

-- foo.kdl
foo {
  f 10
  bar link="bar.kdl"
}

-- bar.kdl
bar {
  b 15
}

-- foo.kdl
foo {
  f 10
  bar {
    b 15 s
  }
}

You can convert a KdlRef to an AssetRef using toRef. For instance, this is how we'd get the value of b from a Foo file:

b <- asset $ do
  foo :: Foo <- "foo.kdl"
  bar <- toRef foo.bar
  pure bar.b