facc356a0a
Typos were found with ``` pip install codespell --upgrade codespell --summary --ignore-words-list enew,forin,fro,happend,hge,ihs,iterm,spred --skip stage0 --check-filenames codespell --summary --ignore-words-list enew,forin,fro,happend,hge,ihs,iterm,spred --skip stage0 --check-filenames --regex '[A-Z][a-z]*' codespell --summary --ignore-words-list enew,forin,fro,happend,hge,ihs,iterm,spred --skip stage0 --check-filenames --regex "\b[a-z']*" ```
35 lines
1.1 KiB
Text
35 lines
1.1 KiB
Text
/-
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Copyright (c) 2025 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: Joachim Breitner
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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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import Lean.Meta.InferType
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open Lean Meta
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/-!
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This module provides builder for efficient `Nat → …` functions based on binary decision trees.
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-/
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/--
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Builds an expression of type `Nat → $type` that returns the `es[i]`, using binary search.
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The array must be non-empty.
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-/
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public def mkNatLookupTable (i : Expr) (type : Expr) (es : Array Expr) : MetaM Expr := do
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if h : es.size = 0 then
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panic! "mkNatLookupTable: expected non-empty array"
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else
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let u ← getLevel type
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let rec go (start stop : Nat) (hstart : start < stop := by omega) (hstop : stop ≤ es.size := by omega) : MetaM Expr := do
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if h : start + 1 = stop then
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return es[start]
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else
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let mid := (start + stop) / 2
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let low ← go start mid
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let high ← go mid stop
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return mkApp4 (mkConst ``cond [u]) type (mkApp2 (mkConst ``Nat.ble) i (mkRawNatLit (mid-1))) low high
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go 0 es.size
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