Diffing(3) OCaml library Diffing(3)

Diffing - Parametric diffing

Module Diffing

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.Style.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

2024-05-31 OCamldoc