The Great Renaming, Chapter 10: map renaming

[jmid]

Still wrapping up loose ends in the renaming adventure, we come across map combinators.

The status is:

Combinator name	QCheck.Gen	QCheck.arbitrary	QCheck2.Gen
map	('a -> 'b) -> 'a t -> 'b t	?rev:('b -> 'a) -> ('a -> 'b) -> 'a arbitrary -> 'b arbitrary	('a -> 'b) -> 'a t -> 'b t
map2	('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t	-	('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t
map3	('a -> 'b -> 'c -> 'd) -> ... -> 'd t	-	('a -> 'b -> 'c -> 'd) -> ... -> 'd t
map4	('a -> 'b -> 'c -> 'd -> 'e) -> ... -> 'e t	-	('a -> 'b -> 'c -> 'd -> 'e) -> ... -> 'e t
map5	('a -> 'b -> 'c -> 'd -> 'e -> 'f) -> ... -> 'f t	-	('a -> 'b -> 'c -> 'd -> 'e -> 'f) -> ... -> 'f t
map_keep_input	('a -> 'b) -> 'a t -> ('a * 'b) t	?print:'b Print.t -> ?small:('b -> int) -> ('a -> 'b) -> 'a arbitrary -> ('a * 'b) arbitrary	-
map_same_type	-	('a -> 'a) -> 'a arbitrary -> 'a arbitrary	-

where I have abbreviated somel map signatures in an attempt to make things fit:

• map3 : ('a -> 'b -> 'c -> 'd) -> 'a t -> 'b t -> 'c t -> 'd t
• map4 : ('a -> 'b -> 'c -> 'd -> 'e) -> 'a t -> 'b t -> 'c t -> 'd t -> 'e t
• map5 : ('a -> 'b -> 'c -> 'd -> 'e -> 'f) -> 'a t -> 'b t -> 'c t -> 'd t -> 'e t -> 'f t

Observations

• map* is hard to preserve shrinkers, printers, hence the omissions from QCheck.arbitrary are natural
  • this is also the reason for the optional rev parameter in QCheck.map
• map_same_type only occurs in QCheck.arbitrary - but for QCheck.Gen and QCheck2.Gen map is equivalent
• map_keep_input is missing from QCheck2.Gen for consistency

This PR therefore adds the missing QCheck2.Gen.map_keep_input : ('a -> 'b) -> 'a t -> ('a * 'b) t, while leaving the rest as is.