Stdcompat: compatibility module for OCaml standard library
Stdcompat is a compatibility layer allowing programs to use some
recent additions to the OCaml standard library while preserving the
ability to be compiled on former versions of OCaml.
The Stdcompat API is not intended to be stable, but there will be
efforts to allow future versions of Stdcompat to be compiled on a
large range of versions of OCaml: Stdcompat should compile (at least)
on every version of OCaml from 3.07 (included).
The module Stdcompat provides some definitions for values and
types introduced in recent versions of the standard library. These
definitions are just aliases to the matching definition of the standard
library if the latter is recent enough. Otherwise, the module
Stdcompat provides an alternative implementation.
The signature of Stdcompat follows the signature of the standard library.
All the modules are defined as sub-modules of Stdcompat.Stdlib, such as
Stdcompat.Stdlib.Pervasives, Stdcompat.Stdlib.List, etc. The module
Stdcompat.Stdlib.Pervasives is included in Stdcompat.Stdlib, and
the module Stdcompat.Stdlib is included in Stdcompat itself.
For instance, the function
Stdcompat.really_input_string is an alias for
Stdcompat.Pervasives.really_input_string,
which is an alias for Stdcompat.Stdlib.Pervasives.really_input_string,
which is itself an alias for
Pervasives.really_input_string when the version of the OCaml
compiler is above 4.02.0, or an alternative definition otherwise.
The types Stdcompat.bytes and Stdcompat.floatarray are aliases
to the built-in ones is the latter are available (above 4.02.0 for
bytes and above 4.06.0 for floatarray), and are aliases to
string and float array respectively otherwise.
Sub-modules match the names of the standard library modules. For
instance, Stdcompat.List.find_opt is an alias for
List.find_opt on 4.05.0 and above, or an alternative definition
otherwise. Definitions from the standard library are reexported so that
Stdcompat can be open without hiding unchanged definitions.
Functors Set.Make, Map.Make, Hashtbl.Make, Weak.Make
are redefined to provide the additional definitions appeared on recent
OCaml releases.
If Pervasives.result, Uchar.t and/or Seq.t are not
provided by the standard library and if the compatibility packages
result, uchar, and/or seq are available via ocamlfind,
then the types Stdcompat.Pervasives.result, Stdcompat.Uchar.t
and Stdcompat.Seq.t are defined as alias to the types defined in
those packages (these packages should then appear before Stdcompat
in the linking chain).
Some redefinitions access to the internal representation of
the data structures when they are abstracted: it is the case for
{Set,Map,Hashtbl,Queue,Stack}.to_seq*,
Hashtbl.filter_map_inplace, Hashtbl.stats, Stack.fold,
Set.find*, Set.map.
Pure (but less efficient) implementations are available by configuring
Stdcompat with ./configure --disable-magic.
Note that redefinitions can still have bad time complexity:
for instance, Set.map uses the function union to rebuild trees
instead of the internal function try_join, because using the
latter would require to redefine too much internal functions.
Redefinitions cannot even guarantee some security fixes: for instance,
seeds and randomization are ignored with Hashtbl prior to 4.00.0.
See the generated documentation (in doc/) for available
definitions.