2 Features of MLton
-
whole-program optimization
-
Because MLton compiles the whole program at once, it can perform
optimization across module boundaries. As a consequence, MLton
often reduces or eliminates the run-time penalty that arises with
separate compilation of SML features such as functors, modules,
polymorphism, and higher-order functions. MLton takes advantage of
having the entire program to perform transformations such as:
defunctorization, monomorphisation, higher-order control-flow
analysis, inlining, unboxing, argument flattening, redundant-argument
removal, constant folding, and representation selection.
Whole-program compilation is an integral part of the design of
MLton and is not likely to change.
- supports the full SML 97 language
-
MLton compiles the Standard ML language as given in The Definition
of Standard ML (Revised)[MTHM97]. 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
Section 14.
- complete basis library
-
MLton implements the latest Standard ML basis library
specification, with a complete implementation of all the required
modules, as well as many of the optional modules. See
Section 8 for details.
- excellent running times
-
MLton generates executables with excellent running times.
For a comparison with other SML compilers, see
http://www.mlton.org/performance.html.
- native integers, reals, and words
-
In MLton, integers and words are 32 bits and arithmetic does not have
any overhead due to tagging. Also, reals 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.
- runtime system supports large arrays
-
In MLton, array lengths can be up to 231 - 1, the largest possible
twos-complement 32 bit integer.
- support for large files
-
In MLton, file positions and sizes are 64-bit integers, so files
can be as large as is supported by the underlying platform.
- several garbage collection strategies
-
The MLton runtime system uses copying, mark-compact, and generational
collection, automatically deciding which to use based on the amount of live
data relative to the amount of RAM. The runtime system tries to keep the heap
within RAM if at all possible.
- standalone executables
-
MLton 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.
- small executables
-
Because of whole-program compilation, MLton can use very aggressive
dead-code elimination, which often leads to smaller executables than
with other SML compilers.
- compiles large programs
-
MLton is sufficiently efficient and robust that it can compile
large programs, including itself (over 100K lines). The distributed
version of MLton was compiled by MLton.
- fast IntInf based on GNU multiprecision library
-
The MLton implementation of arbitrary precision arithmetic (the
IntInf structure) uses the
GNU multiprecision library (GNUmp).
Hence, for IntInf intensive programs, MLton can be an order
of magnitude or more faster than Poly/ML or SML/NJ.
- simple and fast C FFI
-
MLton has a straightforward and fast FFI for calling from SML to C
and from C to SML. See Section 6 for details.
- source-level profiling of allocation and time
-
MLton and mlprof provide source-level profiling information.
See Section 7 for details.
- useful libraries
-
MLton has a collection of libraries that provide useful functionality that
cannot be implemented with the standard basis library. See below for an
overview and Section 9 for details.
- continuations
-
MLton supports continuations via callcc and throw.
- finalization
-
MLton supports finalizable values of arbitrary type.
- interval timers
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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. At some point in
the future, MLton will support Concurrent ML (CML).
- weak pointers
-
MLton suports 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.