OCaml - MLton Standard ML Compiler (SML Compiler)

OCaml is a variant of ML and is similar to Standard ML.

OCaml and SML

Here's a comparison of some aspects of the OCaml and SML languages.

Standard ML has a formal Definition, while OCaml is specified by its lone implementation and informal documentation.
Standard ML has a number of compilers, while OCaml has only one.
OCaml has built-in support for object-oriented programming, while Standard ML does not (however, see ObjectOrientedProgramming).
Andreas Rossberg has a side-by-side comparison of the syntax of SML and OCaml.

Here's a comparison of some aspects of OCaml and MLton.

Both OCaml and MLton have excellent performance.
MLton performs extensive WholeProgramOptimization, which can provide substantial improvements in large, modular programs.
MLton uses native types, like 32-bit integers, without any penalty due to tagging or boxing. OCaml uses 31-bit integers with a penalty due to tagging, and 32-bit integers with a penalty due to boxing.
MLton uses native types, like 64-bit floats, without any penalty due to boxing. OCaml, in some situations, boxes 64-bit floats.
MLton represents arrays of all types unboxed. In OCaml, only arrays of 64-bit floats are unboxed, and then only when it is syntactically apparent.
MLton represents records compactly by reordering and packing the fields.
In MLton, polymorphic and monomorphic code have the same performance. In OCaml, polymorphism can introduce a performance penalty.
In MLton, module boundaries have no impact on performance. In OCaml, moving code between modules can cause a performance penalty.