OCaml 4.02.2

• Add a new class of binary operators with the same syntactic
  precedence as method calls; these operators start with # followed
  by a non-empty sequence of operator symbols (for instance #+, #!?).
  It is also possible to use # as part of these extra symbols
  (for instance ##, or #+#); this is rejected by the type-checker,
  but can be used e.g. by ppx rewriters.
• Add a nonrec keyword for type declarations, allowing to write type nonrec t = t.

See also: detailed list of changes.

OCaml 4.02.1

Bug fixes. See detailed list of changes.

OCaml 4.02.0

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 module Bytes were
  introduced. By default, bytes is a synonym for string, so
  existing code that mutates values of type string still compiles,
  with warnings. Option -safe-string separates the types string
  and bytes, 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
  a let x = a in b, catch exceptions raised by a but not those
  raised by b.

• Module aliases (giving an alternative name to an existing module or
  compilation unit, as in module 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 the printf 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.

OCaml 4.01.0

• It is now possible to have several variant constructors or record
  fields of the same name in scope, and type information will be used
  to disambiguate which one is used -- instead of always using the
  last one. See this post for a more detailed description of the feature.

• New warnings can be activated to warn about identifiers that are
  used after having been shadowed by an open construct. The open
  keyword can be written open! to silence this warning (as method!
  silences the method warning).

• The compiler now suggests possible typos on "unbound identifier"
  errors.

• Infix application operators (|>) and (@@) are added to
  Pervasives.

• The -short-path option changes the way the type-checker prints
  types to pick a short representation (eg. string instead of
  StringSet.elt).

• This release saw a lot of polishing with sets of changes in many
  places: the type system for GADTs, compilation speed with
  -bin-annot, ocamlbuild, the test suite, low-level optimizations,
  etc.

See also: detailed list of changes.

OCaml 4.00.1

Bug fixes. See detailed list of changes.

OCaml 4.00.0

• The name the language is now officially "OCaml", and this name is
  used consistently in all the documentation and tool outputs.
• Generalized Algebraic Data Types (GADTs): this is a powerful
  extension of the type system that provides great flexibility and
  power to the programmer.
• A new and improved ARM back-end.
• Changes to first-class modules: type annotations can now be omitted
  when packing and unpacking modules (and are inferred from context
  whenever possible), and first-class modules can now be unpacked by
  pattern-matching.
• Support for randomized hash tables to avoid denial-of-service
  vulnerabilities.
• Installation of the compiler's internal libraries in
  +compiler-libs for easier access by third-party programming tools.

See also: detailed list of changes.