MLton is run from the command line with a collection of options followed by a file name and a list of files to compile, assemble, and link with. The simplest case is to run mlton foo.sml, where foo.sml contains a valid SML program, in which case MLton compiles the program to produce an executable foo. Since MLton does not support separate compilation, the program must be the entire program you wish to compile. However, the program may refer to signatures and structures defined in the Basis Library.

Larger programs, spanning many files, may be compiled with the ML Basis system. In this case, mlton foo.mlb will compile the complete SML program described by the basis foo.mlb, which may specify both SML files and additional bases. See the MLton Guide for details.

MLton also supports a limited subset of SML/NJ Compilation Manager (CM) files. For example, mlton foo.cm will compile the complete SML program consisting of the concatenation of all the SML files referred to (either directly or indirectly) by foo.cm.

MLton's compile-time options control the name of the output file, the verbosity of compile-time messages, and whether or not certain optimizations are performed. They also can specify which intermediate files are saved and can stop the compilation process early, at some intermediate pass, in which case compilation can be resumed by passing the generated files to MLton. MLton uses the input file suffix to determine the type of input program. The possibilities are .c, .cm, .mlb, .o, and .sml.

With no arguments, MLton prints the version number and exits. For a usage message, run MLton with an invalid switch, e.g. mlton -z. In the explanation below and in the usage message, for flags that take a number of choices (e.g. {true|false}), the first value listed is the default.

-align {4|8}

Aligns object sizes and doubles in memory by the specified alignment. The default varies depending on architecture.

-as-opt option

Pass option to gcc when assembling.

-cc-opt option

Pass option to gcc when compiling C code.

-codegen {native|bytecode|c}

Generate native code, byte code, or C code. With -codegen native, MLton typically compiles more quickly and generates better code.

-const 'name value'

Set the value of a compile-time constant. Here is a list of available constants, their default values, and what they control.

Exn.keepHistory {false|true} Enable MLton.Exn.history. There is a performance cost to setting this to true, both in memory usage of exceptions and in run time, because of additional work that must be performed at each exception construction, raise, and handle.

-default-ann ann

Specify default ML Basis annotations. For example, -default-ann 'warnUnused true' causes unused variable warnings to be enabled by default. Defaults may be overridden by an annotation in an ML Basis file.

-disable-ann ann

Ignore the specified ML Basis annotation in every ML Basis File. For example, to see all match and unused warnings, compile with -default-ann 'warnUnused true', -disable-ann forceUsed, -disable-ann nonexhaustiveMatch, -disable-ann redundantMatch, and -disable-ann warnUnused.

-export-header file

Write to file C prototypes for all of the functions exported from SML to C.

-ieee-fp {false|true}

Cause the native code generator to be pedantic about following the IEEE floating point standard. By default, it is not, because of the performance cost. This only has an effect with -codegen native.

-inline n

Set the inlining threshold used in the optimizer. The threshold is an approximate measure of code size of a procedure. The default is 320.

-keep {g|o|sml}

Save intermediate files. If no -keep argument is given, then only the output file is saved. g generated .S and .c files passed to gcc and the assembler o object (.o) files sml SML file

-link-opt option

Pass option to gcc when linking. You can use this to specify library search paths, e.g. -link-opt -Lpath, and libraries to link with, e.g. -link-opt -lfoo, or even both at the same time, e.g. -link-opt '-Lpath -lfoo'. If you wish to pass an option to the linker, you must use gcc's -Wl, syntax, e.g., -link-opt '-Wl,--export-dynamic'.

-mlb-path-map file

Use file as an ML Basis path map to define additional MLB path variables. Multiple uses of -mlb-path-map are allowed, with variable definitions in later path maps taking precendence over earlier ones.

-output file

Specify the name of the final output file. The default name is the input file name with its suffix removed and an appropriate, possibly empty, suffix added.

-profile {no|alloc|count|time}

Produce an executable that gathers profiling data. When such an executable is run, it will produce an mlmon.out file. The man page on mlprof describes how to extract information from this file.

-profile-branch {false|true}

If true, the profiler will separately gather profiling data for each branch of a function definition, case expression, and if expression.

-profile-stack {false|true}

If true, the profiler will gather profiling data for all functions on the stack, not just the currently executing function.

-runtime arg

Pass argument to the runtime system via @MLton. The argument will be processed before other @MLton command line switches. Multiple uses of -runtime are allowed, and will pass all the arguments in order. If the same runtime switch occurs more than once, then the last setting will take effect. There is no need to supply the leading @MLton or the trailing --; these will be supplied automatically.

An argument to -runtime may contain spaces, which will cause the argument to be treated as a sequence of words by the runtime. For example, the command line: mlton -runtime 'ram-slop 0.4' foo.sml will cause foo to run as if it had been called like foo @MLton ram-slop 0.4 --

An executable created with -runtime stop doesn't proces any @MLton arguments. This is useful to create an executable, e.g. echo, that must treat @MLton like any other command-line argument.

-show-basis file

Pretty print to file the basis defined by the input program.

-show-def-use file

Output def-use information to file. Each identifier that is defined appears on a line, follwed on subequent lines by the position of each use.

-stop {f|g|o|sml|tc}

Specify when to stop. f list of files on stdout (only makes sense when input is foo.cm or foo.mlb) g generated .S and .c files o object (.o) files sml SML file (only makes sense when input is foo.cm or foo.mlb) tc after type checking If you compile -stop g or -stop o, you can resume compilation by running MLton on the generated .c and .S or .o files.

-target {self|...}

Generate an executable that runs on the specified platform. The default is self, which means to compile for the machine that MLton is running on. To use any other target, you must first install a cross compiler. See the MLton Guide for details.

-target-as-opt target option

Like -as-opt, this passes option to gcc when assembling, except it only passes option when the target architecture or operating system is target. Valid values for target are: hppa, powerpc, sparc, x86, cygwin, darwin, freebsd, linux, mingw, netbsd, openbsd, solaris.

-target-cc-opt target option

Like -cc-opt, this passes option to gcc when compiling C code, except it only passes option when the target architecture or operating system is target. Valid values for target are as for -target-as-opt.

-target-link-opt target option

Like -link-opt, this passes option to gcc when linking, except it only passes option when the target architecture or operating system is target. Valid values for target are as for -target-as-opt.

-verbose {0|1|2|3}

How verbose to be about what passes are running. The default is 0. 0 silent 1 calls to compiler, assembler, and linker 2 1, plus intermediate compiler passes 3 2, plus some data structure sizes

It is allowed to have a sequence of @MLton arguments, as in: hello-world @MLton gc-summary -- @MLton fixed-heap 10k -- a b c

Run-time options can also control MLton, as in mlton @MLton fixed-heap 0.5g -- foo.sml

fixed-heap x{k|K|m|M|g|G}

Use a fixed size heap of size x, where x is a real number and the trailing letter indicates its units. k or K 1024 m or M 1,048,576 g or G 1,073,741,824 A value of 0 means to use almost all the RAM present on the machine.

The heap size used by fixed-heap includes all memory allocated by SML code, including memory for the stack (or stacks, if there are multiple threads). It does not, however, include any memory used for code itself or memory used by C globals, the C stack, or malloc.

gc-messages

Print a message at the start and end of every garbage collection.

gc-summary

Print a summary of garbage collection statistics upon program termination.

load-world world

Restart the computation with the file specified by world, which must have been created by a call to MLton.World.save by the same executable.

max-heap x{k|K|m|M|g|G}

Run the computation with an automatically resized heap that is never larger than x, where x is a real number and the trailing letter indicates the units as with fixed-heap. The heap size for max-heap is accounted for as with fixed-heap.

-no-load-world

Disable load-world. This can be used as an argument to the compiler via -runtime no-load-world to create executables that will not load a world. This may be useful to ensure that set-uid executables do not load some strange world.

ram-slop x

Multiply x by the amount of RAM on the machine to obtain what the runtime views as the amount of RAM it can use. Typically x is less than 1, and is used to account for space used by other programs running on the same machine.

stop

Causes the runtime to stop processing @MLton arguments once the next -- is reached. This can be used as an argument to the compiler via -runtime stop to create executables that don't process any @MLton arguments.