NAME

       Diffing -  Parametric diffing

Module

       Module   Diffing

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.

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

       The type of potential changes on a list.

       val map : ('l1 -> 'l2) -> ('r1 -> 'r2) -> ('l1, 'r1, 'eq, 'diff) change -> ('l2, 'r2, 'eq, 'diff) change

       type ('l, 'r, 'eq, 'diff) patch = ('l, 'r, 'eq, 'diff) change list

       A patch is an ordered list of changes.

       val diff : weight:(('l, 'r, 'eq, 'diff) change -> int) -> test:('state  ->  'l  ->  'r  ->  ('eq,  'diff)
       result)  -> update:(('l, 'r, 'eq, 'diff) change -> 'state -> 'state) -> 'state -> 'l array -> 'r array ->
       ('l, 'r, 'eq, 'diff) patch

       diff ~weight ~test ~update state l r computes the diff between l and r , using the initial state state .

       - test st xl xr tests if the elements xl and xr are compatible ( Ok ) or not ( Error ).

       - weight ch returns the weight of the change ch .  Used to find the smallest patch.

       - update ch st returns the new state after applying a change.

   Variadic diffing
       Variadic diffing allows to expand the lists being diffed during diffing.

       type ('l, 'r, 'e, 'd, 'state) update =
        | Without_extensions of (('l, 'r, 'e, 'd) change -> 'state -> 'state)
        | With_left_extensions of (('l, 'r, 'e, 'd) change -> 'state -> 'state * 'l array)
        | With_right_extensions of (('l, 'r, 'e, 'd) change -> 'state -> 'state * 'r array)

       val variadic_diff : weight:(('l, 'r, 'eq, 'diff) change -> int) -> test:('state ->  'l  ->  'r  ->  ('eq,
       'diff)  result)  ->  update:('l, 'r, 'eq, 'diff, 'state) update -> 'state -> 'l array -> 'r array -> ('l,
       'r, 'eq, 'diff) patch

       variadic_diff ~weight ~test ~update state l r behaves as diff with the following difference:

       - update must now be an Diffing.update which indicates in which direction the expansion takes place.