79 lines
1.7 KiB
Text
79 lines
1.7 KiB
Text
/-
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Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Joe Hendrix
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-/
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module
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prelude
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public import Lean.Meta.Basic
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public section
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namespace Lean.Meta
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/--
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Provides an interface for iterating over values that are bundled with the `Meta` state
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they are valid in.
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-/
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protected structure Iterator (α : Type) where
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/-- Function for getting next value and state pair. -/
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next : MetaM (Option (α × Meta.SavedState))
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namespace Iterator
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/--
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Convert a list into an iterator with the current state.
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-/
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def ofList (l : List α) : MetaM (Meta.Iterator α) := do
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let s ← saveState
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let ref ← IO.mkRef l
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let next := do
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restoreState s
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match ← ref.get with
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| [] =>
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pure none
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| r :: l =>
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ref.set l
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pure <| some (r, ←saveState)
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pure { next }
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/--
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Map and filter results of iterator and returning only those values returned
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by `f`.
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-/
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partial def filterMapM (f : α → MetaM (Option β)) (L : Meta.Iterator α) : Meta.Iterator β :=
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{ next := _next }
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where _next := do
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match ← L.next with
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| none =>
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pure none
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| some (v, s) =>
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restoreState s
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let r ← f v
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match r with
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| none =>
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_next
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| some r =>
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pure <| some (r, ←saveState)
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/--
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Find the first value in the iterator while resetting state or call `failure`
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if empty.
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-/
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def head (L : Meta.Iterator α) : MetaM α := do
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match ← L.next with
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| none =>
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failure
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| some (x, s) =>
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restoreState s
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pure x
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/--
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Return the first value returned by the iterator that `f` succeeds on.
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-/
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def firstM (L : Meta.Iterator α) (f : α → MetaM (Option β)) : MetaM β := L.filterMapM f |>.head
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end Iterator
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end Lean.Meta
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