Documentation

Init.Data.Stream

Remark: we considered using the following alternative design

structure Stream (α : Type u) where
  stream : Type u
  next? : stream → Option (α × stream)

class ToStream (collection : Type u) (value : outParam (Type v)) where
  toStream : collection → Stream value

where Stream is not a class, and its state is encapsulated. The key problem is that the type Stream α "lives" in a universe higher than α. This is a problem because we want to use Streams in monadic code.

class ToStream (collection : Type u) (stream : outParam (Type u)) :
  • toStream : collectionstream

Streams are used to implement parallel for statements. Example:

for x in xs, y in ys do
  ...

is expanded into

let mut s := toStream ys
for x in xs do
  match Stream.next? s with
  | none => break
  | some (y, s') =>
    s := s'
    ...
Instances
    class Stream (stream : Type u) (value : outParam (Type v)) :
    Type (max u v)
    • next? : streamOption (value × stream)
    Instances
      def Stream.forIn {ρ : Type u_1} {α : Type u_2} {m : Type u_3 → Type u_4} {β : Type u_3} [Stream ρ α] [Monad m] (s : ρ) (b : β) (f : αβm (ForInStep β)) :
      m β
      Equations
      Instances For
        partial def Stream.forIn.visit {ρ : Type u_1} {α : Type u_2} {m : Type u_3 → Type u_4} {β : Type u_3} [Stream ρ α] [Monad m] (f : αβm (ForInStep β)) (s : ρ) (b : β) :
        m β
        instance instForIn {ρ : Type u_1} {α : Type u_2} {m : Type u_3 → Type u_4} [Stream ρ α] :
        ForIn m ρ α
        Equations
        • instForIn = { forIn := fun {β} [Monad m] => Stream.forIn }
        instance instToStreamList {α : Type u_1} :
        ToStream (List α) (List α)
        Equations
        • instToStreamList = { toStream := fun c => c }
        instance instToStreamArraySubarray {α : Type u_1} :
        Equations
        instance instToStreamSubarray {α : Type u_1} :
        Equations
        • instToStreamSubarray = { toStream := fun a => a }
        Equations
        instance instStreamProdProd {ρ : Type u_1} {α : Type u_2} {γ : Type u_3} {β : Type u_4} [Stream ρ α] [Stream γ β] :
        Stream (ρ × γ) (α × β)
        Equations
        • One or more equations did not get rendered due to their size.
        instance instStreamList {α : Type u_1} :
        Stream (List α) α
        Equations
        • instStreamList = { next? := fun x => match x with | [] => none | a :: as => some (a, as) }
        instance instStreamSubarray {α : Type u_1} :
        Equations
        • One or more equations did not get rendered due to their size.
        Equations
        • instStreamRangeNat = { next? := fun r => if r.start < r.stop then some (r.start, { start := r.start + r.step, stop := r.stop, step := r.step }) else none }
        Equations
        • One or more equations did not get rendered due to their size.