Represent a match as a formula in propositional logic that encodes whether the match matches (abstractly: we only consider types)
Represent a match as a formula in propositional logic that encodes whether the match matches (abstractly: we only consider types)
Interface with user-defined match monad?
if there's a __match
in scope, we use this as the match strategy, assuming it conforms to MatchStrategy as defined below:
Interface with user-defined match monad?
if there's a __match
in scope, we use this as the match strategy, assuming it conforms to MatchStrategy as defined below:
type Matcher[P[_], M[+_], A] = { def flatMap[B](f: P[A] => M[B]): M[B] def orElse[B >: A](alternative: => M[B]): M[B] } abstract class MatchStrategy[P[_], M[+_]] { // runs the matcher on the given input def runOrElse[T, U](in: P[T])(matcher: P[T] => M[U]): P[U] def zero: M[Nothing] def one[T](x: P[T]): M[T] def guard[T](cond: P[Boolean], then: => P[T]): M[T] }
P and M are derived from one's signature (def one[T](x: P[T]): M[T]
)
if no __match
is found, we assume the following implementation (and generate optimized code accordingly)
object __match extends MatchStrategy[({type Id[x] = x})#Id, Option] { def zero = None def one[T](x: T) = Some(x) // NOTE: guard's return type must be of the shape M[T], where M is the monad in which the pattern match should be interpreted def guard[T](cond: Boolean, then: => T): Option[T] = if(cond) Some(then) else None def runOrElse[T, U](x: T)(f: T => Option[U]): U = f(x) getOrElse (throw new MatchError(x)) }
The phase defined by this transform
The phase defined by this transform
A standard phase template
A standard phase template
Names of phases that must run before this phase.
Names of phases that must run before this phase.
Name of the phase that this phase must follow immediately.
Name of the phase that this phase must follow immediately.
Compute the type T implied for a value v
matched by a pattern pat
(with expected type pt
).
Compute the type T implied for a value v
matched by a pattern pat
(with expected type pt
).
Usually, this is the pattern's type because pattern matching implies instance-of checks.
However, Stable Identifier and Literal patterns are matched using ==
,
which does not imply a type for the binder that binds the matched value.
See SI-1503, SI-5024: don't cast binders to types we're not sure they have
TODO: update spec as follows (deviation between **
):
A pattern binder x@p consists of a pattern variable x and a pattern p. The type of the variable x is the static type T **IMPLIED BY** the pattern p. This pattern matches any value v matched by the pattern p **Deleted: , provided the run-time type of v is also an instance of T, ** and it binds the variable name to that value.
Addition:
A pattern p
_implies_ a type T
if the pattern matches only values of the type T
.
Is this component enabled? Default is true.
Is this component enabled? Default is true.
SubComponent are added to a HashSet and two phases are the same if they have the same name
SubComponent are added to a HashSet and two phases are the same if they have the same name
True if this phase runs before all other phases.
True if this phase runs before all other phases. Usually, parser
.
True if this phase is not provided by a plug-in.
True if this phase is not provided by a plug-in.
Create a new phase which applies transformer
Create a new phase which applies transformer
The transformer factory
The transformer factory
The phase corresponding to this subcomponent in the current compiler run
The phase corresponding to this subcomponent in the current compiler run
The name of the phase
The name of the phase
New flags defined by the phase which are not valid before
New flags defined by the phase which are not valid before
New flags defined by the phase which are not valid until immediately after it
New flags defined by the phase which are not valid until immediately after it
Names of phases required by this component.
Names of phases required by this component. Default is Nil
.
Names of phases that must run after this phase.
Names of phases that must run after this phase. Default is Nil
.
True if this phase runs after all other phases.
True if this phase runs after all other phases. Usually, terminal
.
Translate pattern matching.
Either into optimized if/then/else's, or virtualized as method calls (these methods form a zero-plus monad), similar in spirit to how for-comprehensions are compiled.
For each case, express all patterns as extractor calls, guards as 0-ary extractors, and sequence them using
flatMap
(lifting the body of the case into the monad usingone
).Cases are combined into a pattern match using the
orElse
combinator (the implicit failure case is expressed using the monad'szero
).TODO:
(longer-term) TODO: