System.FS.Sim.Stream

Possibly infinite streams of Maybe as.

Streams

data Stream a

A Stream is a stream of Maybe as, which is possibly infinite or definitely finite.

Finiteness is tracked internally and used for shrinking and the Show instance.

Instances

Functor Stream

Defined in System.FS.Sim.Stream

Methods

fmap :: (a -> b) -> Stream a -> Stream b

(<$) :: a -> Stream b -> Stream a

Show a => Show (Stream a)

Fully shows a Stream if it is definitely finite, or prints a placeholder string if it is possibly infinite.

Defined in System.FS.Sim.Stream

Methods

showsPrec :: Int -> Stream a -> ShowS

show :: Stream a -> String

showList :: [Stream a] -> ShowS

Running

runStream :: Stream a -> (Maybe a, Stream a)

Advance the Stream. Return the Maybe a and the remaining Stream.

Returns Nothing by default if the Stream is empty.

Construction

always :: a -> Stream a

Make a Stream that always generates the given a.

empty :: Stream a

Make an empty Stream.

mkInfinite :: [Maybe a] -> Stream a

Make a Stream that is marked as possibly infinite.

repeating :: [Maybe a] -> Stream a

Make a Stream that infinitely repeats the given list.

unsafeMkFinite :: [Maybe a] -> Stream a

UNSAFE: Make a Stream that is marked as definitely finite.

This is unsafe since a user can pass in any list, and evaluating shrink or show on the resulting Stream will diverge. It is the user's responsibility to only pass in a finite list.

Query

null :: Stream a -> Bool

Return True if the stream is empty.

A stream consisting of only Nothings (even if it is only one) is not considered to be empty.

Generation and shrinking

genFinite

Arguments

:: Int

Requested size of finite stream. Tip: use genMaybe.

-> Gen (Maybe a)

-> Gen (Stream a)

Generate a finite Stream of length n.

genInfinite

Arguments

:: Gen (Maybe a)

Tip: use genMaybe.

-> Gen (Stream a)

Generate an infinite Stream.

genMaybe

Arguments

:: Int

Likelihood of Nothing

-> Int

Likelihood of Just a

-> Gen a

-> Gen (Maybe a)

Make a Maybe a generator based on an a generator.

Each element has a chance of being either Nothing or an element generated with the given a generator (wrapped in a Just).

The first argument is the likelihood (as used by frequency) of a Just where Nothing has likelihood 2.

genMaybe'

Arguments

:: Int

Likelihood of Just a

-> Gen a

-> Gen (Maybe a)

Like genMaybe, but with the likelihood of Nothing fixed to 2. frequency

shrinkStream :: Stream a -> [Stream a]

Shrink a stream like it is an InfiniteList.

Possibly infinite streams are shrunk differently than lists that are definitely finite, which is to ensure that shrinking terminates. * Possibly infinite streams are shrunk by taking finite prefixes of the argument stream. As such, shrinking a possibly infinite stream creates definitely finite streams. * Definitely finite streams are shrunk like lists are shrunk normally, preserving that the created streams are still definitely finite.