and helper functions. Signed-off-by: Matthias Goergens <[email protected]>
stdext/Makefile | 2 +- stdext/either.ml | 24 ++++++++++++++++++++++++ stdext/either.mli | 18 ++++++++++++++++++ 3 files changed, 43 insertions(+), 1 deletions(-)
# HG changeset patch # User Matthias Goergens <[email protected]> # Date 1274194687 -3600 # Node ID 1fa93dc2f9eb79c868c85eb1111f97d84433705a # Parent e19b02ff262bcd15faa1fa3c4f88659812ce9646 stdext/Either: A module for type ('a, 'b) t = Left of 'a | Right of 'b and helper functions. Signed-off-by: Matthias Goergens <[email protected]> diff --git a/stdext/Makefile b/stdext/Makefile --- a/stdext/Makefile +++ b/stdext/Makefile @@ -22,7 +22,7 @@ OCAML_TEST_LIB = $(shell ocamlfind query STDEXT_OBJS = fun listext filenameext stringext arrayext hashtblext pervasiveext threadext ring \ qring fring opt bigbuffer unixext range vIO trie config date encodings fe fecomms \ - forkhelpers gzip sha1sum zerocheck base64 backtrace tar mapext os + forkhelpers gzip sha1sum zerocheck base64 backtrace tar mapext os either INTF = $(foreach obj, $(STDEXT_OBJS),$(obj).cmi) LIBS = stdext.cma stdext.cmxa diff --git a/stdext/either.ml b/stdext/either.ml new file mode 100644 --- /dev/null +++ b/stdext/either.ml @@ -0,0 +1,24 @@ +open Pervasiveext + +type ('a,'b) t = Left of 'a | Right of 'b + +let left x = Left x +let right x = Right x +let is_left = function + | Left _ -> true + | Right _ -> false +let is_right x = not ++ is_left $ x +let to_option = function + | Right x -> Some x + | Left _ -> None + +let cat_right l = Opt.cat_some ++ List.map to_option $ l + +let join = function + | Right (Right x) -> Right x + | Left x -> Left (Left x) + | Right (Left x) -> Left (Right x) + +let swap = function + | Right x -> Left x + | Left x -> Right x diff --git a/stdext/either.mli b/stdext/either.mli new file mode 100644 --- /dev/null +++ b/stdext/either.mli @@ -0,0 +1,18 @@ +(* Inspired by Haskell's Either, as a way to enhance option with + information about what went wrong. + + Right is commonly used for success + Left is commonly used for failure. + *) + +type ('a,'b) t = Left of 'a | Right of 'b +val left : 'a -> ('a, 'b) t +val right: 'b -> ('a, 'b) t +val is_left: ('a, 'b) t -> bool +val is_right: ('a, 'b) t -> bool + +val cat_right: ('a, 'b) t list -> 'b list +(* Brings Right values closer to the surface. *) +val join: ('a, ('b, 'c) t) t -> (('a, 'b) t, 'c) t + +val swap : ('a, 'b) t -> ('b, 'a) t
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