---
name: "Diffing_with_keys"
section: "3o"
platform: "linux"
package: "ocaml"
version: "5.5.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Diffing_with_keys"
---

# Diffing\_with\_keys(3o)

When diffing lists where each element has a distinct key, we can refine the diffing patch by introducing two composite edit moves: swaps and moves.

## NAME

Diffing\_with\_keys - When diffing lists where each element has a distinct key, we can refine the diffing patch by introducing two composite edit moves: swaps and moves.

## Module

Module   Diffing\_with\_keys

## Documentation

Module **Diffing\_with\_keys**\
  :  **sig end**

When diffing lists where each element has a distinct key, we can refine the diffing patch by introducing two composite edit moves: swaps and moves.

**Swap** s exchange the position of two elements.  **Swap** cost is set to **2 \* change - epsilon** . **Move** s change the position of one element.  **Move** cost is set to **delete + addition - epsilon** .

When the cost  **delete + addition** is greater than  **change** and with those specific weights, the optimal patch with  **Swap** s and  **Move** s can be computed directly and cheaply from the original optimal patch.

*type* **'a** *with\_pos* = {\
  pos :  **int** ;\
  data :  **'a** ;\
  }

*val with\_pos* :  **'a list -\> 'a with\_pos list**

*type* **('l, 'r, 'diff)** *mismatch* =\
  \| Name **of {**\
  pos :  **int** ;\
  got :  **string** ;\
  expected :  **string** ;\
  types\_match :  **bool** ;\
  }\
  \| Type **of {**\
  pos :  **int** ;\
  got :  **'l** ;\
  expected :  **'r** ;\
  reason :  **'diff** ;\
  }

*type* **('l, 'r, 'diff)** *change* =\
  \| Change **of** **('l, 'r, 'diff) mismatch**\
  \| Swap **of {**\
  pos :  **int \* int** ;\
  first :  **string** ;\
  last :  **string** ;\
  }\
  \| Move **of {**\
  name :  **string** ;\
  got :  **int** ;\
  expected :  **int** ;\
  }\
  \| Insert **of {**\
  pos :  **int** ;\
  insert :  **'r** ;\
  }\
  \| Delete **of {**\
  pos :  **int** ;\
  delete :  **'l** ;\
  }

This specialized version of changes introduces two composite changes:  **Move** and  **Swap**

*val prefix* :  **('l, 'r, 'diff) change Format\_doc.printer**

*module Define :* **(D : sig end) -\> sig end**