Features - MLton Standard ML Compiler (SML Compiler)

Supports the full SML 97 language as given in The Definition of Standard ML (Revised).
If there is a program that is valid according to The Definition that is rejected by MLton, or a program that is invalid according to the Definition that is accepted by MLton, it is a bug. For a list of known bugs, see UnresolvedBugs.
A complete implementation of the Basis Library.
MLton's implementation matches latest Basis Library specification, and includes a complete implementation of all the required modules, as well as many of the optional modules.
Generates standalone executables.
No additional code or libraries are necessary in order to run an executable, except for the standard shared libraries. MLton can also generate statically linked executables.
Compiles large programs.
MLton is sufficiently efficient and robust that it can compile large programs, including itself (over 140K lines). The distributed version of MLton was compiled by MLton.
Support for large amounts of memory (up to 4G on 32-bit systems; more on 64-bit systems).
Support for large array lengths (up to 2³¹ - 1 on 32-bit systems; up to 2⁶³ - 1 on 64-bit systems).
Support for large files, using 64-bit file positions.

Performance

Executables have excellent running times.
Generates small executables.
MLton takes advantage of whole-program compilation to perform very aggressive dead-code elimination, which often leads to smaller executables than with other SML compilers.
Untagged and unboxed native integers, reals, and words.
In MLton, integers and words are 8 bits, 16 bits, 32 bits, and 64 bits and arithmetic does not have any overhead due to tagging or boxing. Also, reals (32-bit and 64-bit) are stored unboxed, avoiding any overhead due to boxing.
Unboxed native arrays.
In MLton, an array (or vector) of integers, reals, or words uses the natural C-like representation. This is fast and supports easy exchange of data with C. Monomorphic arrays (and vectors) use the same C-like representations as their polymorphic counterparts.
Multiple garbage collection strategies.
Fast arbitrary precision arithmetic (IntInf) based on the GnuMP.
For IntInf intensive programs, MLton can be an order of magnitude or more faster than Poly/ML or SML/NJ.

Tools

Source-level Profiling of both time and allocation.
MLLex lexer generator
MLYacc parser generator
MLNLFFIGen foreign-function-interface generator

Extensions

A simple and fast C ForeignFunctionInterface that supports calling from SML to C and from C to SML.
The ML Basis system for programming in the very large, separate delivery of library sources, and more.
A number of extension libraries that provide useful functionality that cannot be implemented with the Basis Library. See below for an overview and MLtonStructure for details.

continuations
MLton supports continuations via callcc and throw.
finalization
MLton supports finalizable values of arbitrary type.
interval timers
MLton supports the functionality of the C setitimer function.
random numbers
MLton has functions similar to the C rand and srand functions, as well as support for access to /dev/random and /dev/urandom.
resource limits
MLton has functions similar to the C getrlimit and setrlimit functions.
resource usage
MLton supports a subset of the functionality of the C getrusage function.
signal handlers
MLton supports signal handlers written in SML. Signal handlers run in a separate MLton thread, and have access to the thread that was interrupted by the signal. Signal handlers can be used in conjunction with threads to implement preemptive multitasking.
size primitive
MLton includes a primitive that returns the size (in bytes) of any object. This can be useful in understanding the space behavior of a program.
system logging
MLton has a complete interface to the C syslog function.
threads
MLton has support for its own threads, upon which either preemptive or non-preemptive multitasking can be implemented. MLton also has support for Concurrent ML (CML).
weak pointers
MLton supports weak pointers, which allow the garbage collector to reclaim objects that it would otherwise be forced to keep. Weak pointers are also used to provide finalization.
world save and restore
MLton has a facility for saving the entire state of a computation to a file and restarting it later. This facility can be used for staging and for checkpointing computations. It can even be used from within signal handlers, allowing interrupt driven checkpointing.