40e8f4c5fb
This PR turns on the new `do` elaborator in Init, Lean, Std, Lake and the testsuite. --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
61 lines
1.8 KiB
Text
61 lines
1.8 KiB
Text
/-
|
|
Copyright (c) 2024-2025 Lean FRO, LLC. All rights reserved.
|
|
Released under Apache 2.0 license as described in the file LICENSE.
|
|
Authors: David Thrane Christiansen
|
|
-/
|
|
module
|
|
|
|
prelude
|
|
public import Init.Data.String.Basic
|
|
import Init.Data.Vector.Basic
|
|
import Init.Data.Nat.Order
|
|
import Init.Data.Order.Lemmas
|
|
import Init.Data.Range
|
|
import Init.While
|
|
|
|
set_option linter.missingDocs true
|
|
|
|
namespace Lean.EditDistance
|
|
|
|
/--
|
|
Computes the Levenshtein distance between two strings, up to some cutoff.
|
|
|
|
If the return value is `none`, then the distance is certainly greater than the cutoff value, but a
|
|
returned `some` does not necessarily indicate that the edit distance is less than or equal to the
|
|
cutoff.
|
|
-/
|
|
public def levenshtein (str1 str2 : String) (cutoff : Nat) : Option Nat := Id.run do
|
|
let len1 := str1.length
|
|
let len2 := str2.length
|
|
|
|
-- The lower bound on the Levenshtein distance is the difference in lengths
|
|
if max len1 len2 - min len1 len2 > cutoff then return none
|
|
|
|
let mut v0 := Vector.replicate (len2 + 1) 0
|
|
let mut v1 := v0
|
|
|
|
for h : i in [0:v0.size] do
|
|
v0 := v0.set i i
|
|
let mut iter1 := str1.startPos
|
|
let mut i := 0
|
|
while h1 : ¬iter1.IsAtEnd do
|
|
v1 := v1.set 0 (i+1)
|
|
let mut iter2 := str2.startPos
|
|
let mut j : Fin (len2 + 1) := 0
|
|
while h2 : ¬iter2.IsAtEnd do
|
|
let j' : Fin (len2 + 1) := j + 1
|
|
let deletionCost := v0[j'] + 1
|
|
let insertionCost := v1[j] + 1
|
|
let substCost :=
|
|
if iter1.get h1 == iter2.get h2 then v0[j]
|
|
else v0[j] + 1
|
|
let cost := min (min deletionCost insertionCost) substCost
|
|
v1 := v1.set j' cost
|
|
iter2 := iter2.next h2
|
|
j := j + 1
|
|
iter1 := iter1.next h1
|
|
i := i + 1
|
|
-- Terminate early if it's impossible that the result is below the cutoff
|
|
if v1.all (· > cutoff) then return none
|
|
v0 := v1
|
|
some v0[len2]
|