Diffing(3) OCaml library Diffing(3)

# [NAME](#NAME)

Diffing - Parametric diffing

# [Module](#Module)

Module Diffing

# [Documentation](#Documentation)

Module **Diffing**  
: **sig end**

Parametric diffing

This module implements diffing over lists of arbitrary content. It is parameterized by

-The content of the two lists

-The equality witness when an element is kept

-The diffing witness when an element is changed

Diffing is extended to maintain state depending on the computed changes while walking through the two lists.

The underlying algorithm is a modified Wagner-Fischer algorithm (see <https://en.wikipedia.org/wiki/Wagner%E2%80%93Fischer\_algorithm>).

We provide the following guarantee: Given two lists **l** and **r** , if different patches result in different states, we say that the state diverges.

-We always return the optimal patch on prefixes of **l** and **r** on which state does not diverge.

-Otherwise, we return a correct but non-optimal patch where subpatches with no divergent states are optimal for the given initial state.

More precisely, the optimality of Wagner-Fischer depends on the property that the edit-distance between a k-prefix of the left input and a l-prefix of the right input d(k,l) satisfies

d(k,l) = min ( del\_cost + d(k-1,l), insert\_cost + d(k,l-1), change\_cost + d(k-1,l-1) )

Under this hypothesis, it is optimal to choose greedily the state of the minimal patch transforming the left k-prefix into the right l-prefix as a representative of the states of all possible patches transforming the left k-prefix into the right l-prefix.

If this property is not satisfied, we can still choose greedily a representative state. However, the computed patch is no more guaranteed to be globally optimal. Nevertheless, it is still a correct patch, which is even optimal among all explored patches.

*module type Defs =* **sig end**

The core types of a diffing implementation

*type change\_kind* =  
| Deletion  
| Insertion  
| Modification  
| Preservation

The kind of changes which is used to share printing and styling across implementation

*val prefix* : **Format.formatter -> int * change\_kind -> unit**

*val style* : **change\_kind -> Misc.Color.style list**

*type* **('left, 'right, 'eq, 'diff)** *change* =  
| Delete **of** **'left**  
| Insert **of** **'right**  
| Keep **of** **'left * 'right * 'eq**  
| Change **of** **'left * 'right * 'diff**

*val classify* : **('a, 'b, 'c, 'd) change -> change\_kind**

*module Define :* **functor (D : Defs) -> sig end**

**Define(Defs)** creates the diffing types from the types defined in **Defs** and the functors that need to be instantatied with the diffing algorithm parameters

2026-09-15 OCamldoc

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Document: Diffing(3o) from ocaml-4 4.14.4-r3 (Chainguard OS)
Source: https://github.com/ocaml/ocaml