mirror of https://github.com/sbt/sbt.git
261 lines
11 KiB
Scala
261 lines
11 KiB
Scala
package sbt
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package appmacro
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import Classes.Applicative
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import Types.Id
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/** The separate hierarchy from Applicative/Monad is for two reasons.
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*
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* 1. The type constructor is represented as an abstract type because a TypeTag cannot represent a type constructor directly.
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* 2. The applicative interface is uncurried.
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*/
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trait Instance
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{
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type M[x]
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def app[K[L[x]], Z](in: K[M], f: K[Id] => Z)(implicit a: AList[K]): M[Z]
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def map[S,T](in: M[S], f: S => T): M[T]
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def pure[T](t: () => T): M[T]
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}
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trait Convert
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{
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def apply[T: c.TypeTag](c: scala.reflect.makro.Context)(in: c.Tree): c.Tree
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}
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trait MonadInstance extends Instance
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{
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def flatten[T](in: M[M[T]]): M[T]
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}
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object InputWrapper
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{
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def wrap[T](in: Any): T = error("This method is an implementation detail and should not be referenced.")
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}
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import scala.reflect._
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import makro._
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object Instance
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{
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final val DynamicDependencyError = "Illegal dynamic dependency."
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final val DynamicReferenceError = "Illegal dynamic reference."
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final val ApplyName = "app"
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final val FlattenName = "flatten"
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final val PureName = "pure"
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final val MapName = "map"
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final val InstanceTCName = "M"
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final val WrapName = "wrap"
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final class Input[U <: Universe with Singleton](val tpe: U#Type, val expr: U#Tree, val local: U#ValDef)
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/** Implementation of a macro that provides a direct syntax for applicative functors and monads.
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* It is intended to be used in conjunction with another macro that conditions the inputs.
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*
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* This method processes the Tree `t` to find inputs of the form `InputWrapper.wrap[T]( input )`
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* This form is typically constructed by another macro that pretends to be able to get a value of type `T`
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* from a value convertible to `M[T]`. This `wrap(input)` form has two main purposes.
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* First, it identifies the inputs that should be transformed.
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* Second, it allows the input trees to be wrapped for later conversion into the appropriate `M[T]` type by `convert`.
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* This wrapping is necessary because applying the first macro must preserve the original type,
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* but it is useful to delay conversion until the outer, second macro is called. The `wrap` method accomplishes this by
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* allowing the original `Tree` and `Type` to be hidden behind the raw `T` type. This method will remove the call to `wrap`
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* so that it is not actually called at runtime.
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*
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* Each `input` in each expression of the form `InputWrapper.wrap[T]( input )` is transformed by `convert`.
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* This transformation converts the input Tree to a Tree of type `M[T]`.
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* The original wrapped expression `wrap(input)` is replaced by a reference to a new local `val $x: T`, where `$x` is a fresh name.
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* These converted inputs are passed to `builder` as well as the list of these synthetic `ValDef`s.
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* The `TupleBuilder` instance constructs a tuple (Tree) from the inputs and defines the right hand side of the vals
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* that unpacks the tuple containing the results of the inputs.
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*
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* The constructed tuple of inputs and the code that unpacks the results of the inputs are then passed to the `i`,
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* which is an implementation of `Instance` that is statically accessible.
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* An Instance defines a applicative functor associated with a specific type constructor and, if it implements MonadInstance as well, a monad.
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* Typically, it will be either a top-level module or a stable member of a top-level module (such as a val or a nested module).
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* The `with Singleton` part of the type verifies some cases at macro compilation time,
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* while the full check for static accessibility is done at macro expansion time.
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* Note: Ideally, the types would verify that `i: MonadInstance` when `t.isRight`.
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* With the various dependent types involved, this is not worth it.
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*
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* The `t` argument is the argument of the macro that will be transformed as described above.
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* If the macro that calls this method is for a multi-input map (app followed by map),
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* `t` should be the argument wrapped in Left.
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* If this is for multi-input flatMap (app followed by flatMap),
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* this should be the argument wrapped in Right.
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*/
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def contImpl[T: c.TypeTag](c: Context, i: Instance with Singleton, convert: Convert, builder: TupleBuilder)(t: Either[c.Expr[T], c.Expr[i.M[T]]])(
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implicit tt: c.TypeTag[T], mt: c.TypeTag[i.M[T]], it: c.TypeTag[i.type]): c.Expr[i.M[T]] =
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{
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import c.universe.{Apply=>ApplyTree,_}
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import scala.tools.nsc.Global
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// Used to access compiler methods not yet exposed via the reflection/macro APIs
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val global: Global = c.universe.asInstanceOf[Global]
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val util = ContextUtil[c.type](c)
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val mTC: Type = util.extractTC(i, InstanceTCName)
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// the tree for the macro argument
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val (tree, treeType) = t match {
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case Left(l) => (l.tree, tt.tpe.normalize)
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case Right(r) => (r.tree, mt.tpe.normalize)
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}
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val instanceSym = util.singleton(i)
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// A Tree that references the statically accessible Instance that provides the actual implementations of map, flatMap, ...
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val instance = Ident(instanceSym)
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val parameterModifiers = Modifiers(Flag.PARAM)
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val wrapperSym = util.singleton(InputWrapper)
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val wrapMethodSymbol = util.method(wrapperSym, WrapName)
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def isWrapper(fun: Tree) = fun.symbol == wrapMethodSymbol
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type In = Input[c.universe.type]
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var inputs = List[In]()
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// constructs a ValDef with a parameter modifier, a unique name, with the provided Type and with an empty rhs
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def freshMethodParameter(tpe: Type): ValDef =
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ValDef(parameterModifiers, freshTermName("p"), typeTree(tpe), EmptyTree)
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def freshTermName(prefix: String) = newTermName(c.fresh("$" + prefix))
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def typeTree(tpe: Type) = TypeTree().setType(tpe)
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// constructs a function that applies f to each subtree of the input tree
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def visitor(f: Tree => Unit): Tree => Unit =
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{
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val v: Transformer = new Transformer {
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override def transform(tree: Tree): Tree = { f(tree); super.transform(tree) }
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}
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(tree: Tree) => v.transform(tree)
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}
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/* Local definitions in the macro. This is used to ensure
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* references are to M instances defined outside of the macro call.*/
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val defs = new collection.mutable.HashSet[Symbol]
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// a reference is illegal if it is to an M instance defined within the scope of the macro call
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def illegalReference(sym: Symbol): Boolean =
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sym != null && sym != NoSymbol && defs.contains(sym)
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// a function that checks the provided tree for illegal references to M instances defined in the
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// expression passed to the macro and for illegal dereferencing of M instances.
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val checkQual = visitor {
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case s @ ApplyTree(fun, qual :: Nil) => if(isWrapper(fun)) c.error(s.pos, DynamicDependencyError)
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case id @ Ident(name) if illegalReference(id.symbol) => c.error(id.pos, DynamicReferenceError)
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case _ => ()
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}
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// adds the symbols for all non-Ident subtrees to `defs`.
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val defSearch = visitor {
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case _: Ident => ()
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case tree => if(tree.symbol ne null) defs += tree.symbol;
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}
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// transforms the original tree into calls to the Instance functions pure, map, ...,
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// resulting in a value of type M[T]
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def makeApp(body: Tree): Tree =
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inputs match {
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case Nil => pure(body)
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case x :: Nil => single(body, x)
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case xs => arbArity(body, xs)
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}
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// no inputs, so construct M[T] via Instance.pure or pure+flatten
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def pure(body: Tree): Tree =
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{
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val typeApplied = TypeApply(Select(instance, PureName), typeTree(treeType) :: Nil)
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val p = ApplyTree(typeApplied, Function(Nil, body) :: Nil)
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if(t.isLeft) p else flatten(p)
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}
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// m should have type M[M[T]]
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// the returned Tree will have type M[T]
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def flatten(m: Tree): Tree =
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{
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val typedFlatten = TypeApply(Select(instance, FlattenName), typeTree(tt.tpe) :: Nil)
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ApplyTree(typedFlatten, m :: Nil)
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}
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// calls Instance.map or flatmap directly, skipping the intermediate Instance.app that is unnecessary for a single input
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def single(body: Tree, input: In): Tree =
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{
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val variable = input.local
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val param = ValDef(parameterModifiers, variable.name, variable.tpt, EmptyTree)
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val typeApplied = TypeApply(Select(instance, MapName), variable.tpt :: typeTree(treeType) :: Nil)
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val mapped = ApplyTree(typeApplied, input.expr :: Function(param :: Nil, body) :: Nil)
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if(t.isLeft) mapped else flatten(mapped)
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}
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// calls Instance.app to get the values for all inputs and then calls Instance.map or flatMap to evaluate the body
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def arbArity(body: Tree, inputs: List[In]): Tree =
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{
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val result = builder.make(c)(mTC, inputs)
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val param = freshMethodParameter( appliedType(result.representationC, util.idTC :: Nil) )
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val bindings = result.extract(param)
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val f = Function(param :: Nil, Block(bindings, body))
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val ttt = typeTree(treeType)
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val typedApp = TypeApply(Select(instance, ApplyName), typeTree(result.representationC) :: ttt :: Nil)
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val app = ApplyTree(ApplyTree(typedApp, result.input :: f :: Nil), result.alistInstance :: Nil)
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if(t.isLeft) app else flatten(app)
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}
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// called when transforming the tree to add an input
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// for `qual` of type M[A], and a selection qual.value,
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// the call is addType(Type A, Tree qual)
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// the result is a Tree representing a reference to
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// the bound value of the input
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def addType(tpe: Type, qual: Tree): Tree =
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{
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checkQual(qual)
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val vd = util.freshValDef(tpe, qual.symbol)
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inputs ::= new Input(tpe, qual, vd)
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Ident(vd.name)
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}
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// the main tree transformer that replaces calls to InputWrapper.wrap(x) with
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// plain Idents that reference the actual input value
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object appTransformer extends Transformer
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{
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override def transform(tree: Tree): Tree =
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tree match
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{
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case ApplyTree(TypeApply(fun, t :: Nil), qual :: Nil) if isWrapper(fun) =>
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val tag = c.TypeTag(t.tpe)
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addType(t.tpe, convert(c)(qual)(tag) )
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case _ => super.transform(tree)
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}
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}
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// collects all definitions in the tree. used for finding illegal references
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defSearch(tree)
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// applies the transformation
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// resetting attributes: a) must be local b) must be done
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// on the transformed tree and not the wrapped tree or else there are obscure errors
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val tr = makeApp( c.resetLocalAttrs(appTransformer.transform(tree)) )
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c.Expr[i.M[T]](tr)
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}
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import Types._
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implicit def applicativeInstance[A[_]](implicit ap: Applicative[A]): Instance { type M[x] = A[x] } = new Instance
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{
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type M[x] = A[x]
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def app[ K[L[x]], Z ](in: K[A], f: K[Id] => Z)(implicit a: AList[K]) = a.apply[A,Z](in, f)
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def map[S,T](in: A[S], f: S => T) = ap.map(f, in)
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def pure[S](s: () => S): M[S] = ap.pure(s())
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}
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type AI[A[_]] = Instance { type M[x] = A[x] }
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def compose[A[_], B[_]](implicit a: AI[A], b: AI[B]): Instance { type M[x] = A[B[x]] } = new Composed[A,B](a,b)
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// made a public, named, unsealed class because of trouble with macros and inference when the Instance is not an object
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class Composed[A[_], B[_]](a: AI[A], b: AI[B]) extends Instance
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{
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type M[x] = A[B[x]]
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def pure[S](s: () => S): A[B[S]] = a.pure(() => b.pure(s))
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def map[S,T](in: M[S], f: S => T): M[T] = a.map(in, (bv: B[S]) => b.map(bv, f))
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def app[ K[L[x]], Z ](in: K[M], f: K[Id] => Z)(implicit alist: AList[K]): A[B[Z]] =
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{
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val g: K[B] => B[Z] = in => b.app[K, Z](in, f)
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type Split[ L[x] ] = K[ (L ∙ B)#l ]
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a.app[Split, B[Z]](in, g)(AList.asplit(alist))
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}
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}
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}
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