Some of the highlights in release 4.02 are:
-
In a first step towards making strings immutable, a type bytes of
mutable byte arrays and a supporting library moduleBytes
were
introduced. By default,bytes
is a synonym forstring
, so
existing code that mutates values of typestring
still compiles,
with warnings. Option-safe-string
separates the typesstring
andbytes
, making strings immutable. -
The
match
construct was extended to discriminate not just on the
value of its argument expression, but also on exceptions arising out
of the evaluation of this expression. This solves an old problem: in
alet x = a in b
, catch exceptions raised bya
but not those
raised byb
. -
Module aliases (giving an alternative name to an existing module or
compilation unit, as inmodule M = AnotherModule
) are now tracked
specially by the type system and the compiler. This enables not only
more precise typing of applicative functors, but also more precise
dependency analysis at link-time, potentially reducing the size of
executables. -
Annotations can now be attached to most syntactic elements of OCaml
sources (expressions, definitions, type declarations, etc). These
annotations are used by the compiler (e.g. to warn on uses of
functions annotated as deprecated) but also by "ppx" preprocessors,
to guide rewriting of abstract syntax trees. -
Extensible data types can be declared (
type t = ..
) then later
extended with new constructors (type t += A of int
). This
generalizes the handling of the exn type of exception values. -
Functors and functor applications can now take a special () argument
to force generativity of abstract types. -
New toplevel directives
#show_type
,#show_modules
, etc, to query
the toplevel environment. -
Performance of
ocamlopt
-generated code is improved on some
programs through more aggressive constant propagation, two new
optimization passes (dead code elimination and common subexpression
elimination), better compilation of pattern-matching over strings,
optimized representation of constant exceptions, and GC tuning for
large memory heaps. -
The format strings argument of
printf
functions are now
represented as a GADT. This speeds up theprintf
functions
considerably, and leads to more precise typechecking of format
strings. -
The native-code compiler now supports the AArch64 (ARM 64 bits)
architecture. -
The Camlp4 preprocessor and the Labltk library were split off the
distribution. They are now separate projects.
See also: detailed list of changes.