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Module Sys

module Sys: sig .. end
System interface.

Every function in this module raises Sys_error with an informative message when the underlying system call signal an error.

type backend_type =
| Native
| Bytecode
| Other of string (*
Currently, the official distribution only supports Native and Bytecode, but it can be other backends with alternative compilers, for example, javascript
*) 
val argv : string array
The command line arguments given to the process. The first element is the command name used to invoke the program. The following elements are the command-line arguments given to the program.
val executable_name : string
The name of the file containing the executable currently running.
val file_exists : string -> bool
Test if a file with the given name exists.
val is_directory : string -> bool
Returns true if the given name refers to a directory, false if it refers to another kind of file. Raise Sys_error if no file exists with the given name.
val remove : string -> unit
Remove the given file name from the file system.
val rename : string -> string -> unit
Rename a file. The first argument is the old name and the second is the new name. If there is already another file under the new name, rename may replace it, or raise an exception, depending on your operating system.
val getenv : string -> string
Return the value associated to a variable in the process environment. Raise Not_found if the variable is unbound.
val command : string -> int
Execute the given shell command and return its exit code.
val time : unit -> float
Return the processor time, in seconds, used by the program since the beginning of execution.
val chdir : string -> unit
Change the current working directory of the process.
val getcwd : unit -> string
Return the current working directory of the process.
val readdir : string -> string array
Return the names of all files present in the given directory. Names denoting the current directory and the parent directory ("." and ".." in Unix) are not returned. Each string in the result is a file name rather than a complete path. There is no guarantee that the name strings in the resulting array will appear in any specific order; they are not, in particular, guaranteed to appear in alphabetical order.
val interactive : bool ref
This reference is initially set to false in standalone programs and to true if the code is being executed under the interactive toplevel system ocaml.
val os_type : string
Operating system currently executing the OCaml program. One of 
val backend_type : backend_type
Backend type currently executing the OCaml program. @ since 4.04.0
val unix : bool
True if Sys.os_type = "Unix".
val win32 : bool
True if Sys.os_type = "Win32".
val cygwin : bool
True if Sys.os_type = "Cygwin".
val word_size : int
Size of one word on the machine currently executing the OCaml program, in bits: 32 or 64.
val int_size : int
Size of an int. It is 31 bits (resp. 63 bits) when using the OCaml compiler on a 32 bits (resp. 64 bits) platform. It may differ for other compilers, e.g. it is 32 bits when compiling to JavaScript.
val big_endian : bool
Whether the machine currently executing the Caml program is big-endian.
val max_string_length : int
Maximum length of strings and byte sequences.
val max_array_length : int
Maximum length of a normal array. The maximum length of a float array is max_array_length/2 on 32-bit machines and max_array_length on 64-bit machines.
val runtime_variant : unit -> string
Return the name of the runtime variant the program is running on. This is normally the argument given to -runtime-variant at compile time, but for byte-code it can be changed after compilation.
val runtime_parameters : unit -> string
Return the value of the runtime parameters, in the same format as the contents of the OCAMLRUNPARAM environment variable.
Signal handling
type signal_behavior =
| Signal_default
| Signal_ignore
| Signal_handle of (int -> unit)
What to do when receiving a signal: 
val signal : int -> signal_behavior -> signal_behavior
Set the behavior of the system on receipt of a given signal. The first argument is the signal number. Return the behavior previously associated with the signal. If the signal number is invalid (or not available on your system), an Invalid_argument exception is raised.
val set_signal : int -> signal_behavior -> unit
Same as Sys.signal but return value is ignored.
Signal numbers for the standard POSIX signals.
val sigabrt : int
Abnormal termination
val sigalrm : int
Timeout
val sigfpe : int
Arithmetic exception
val sighup : int
Hangup on controlling terminal
val sigill : int
Invalid hardware instruction
val sigint : int
Interactive interrupt (ctrl-C)
val sigkill : int
Termination (cannot be ignored)
val sigpipe : int
Broken pipe
val sigquit : int
Interactive termination
val sigsegv : int
Invalid memory reference
val sigterm : int
Termination
val sigusr1 : int
Application-defined signal 1
val sigusr2 : int
Application-defined signal 2
val sigchld : int
Child process terminated
val sigcont : int
Continue
val sigstop : int
Stop
val sigtstp : int
Interactive stop
val sigttin : int
Terminal read from background process
val sigttou : int
Terminal write from background process
val sigvtalrm : int
Timeout in virtual time
val sigprof : int
Profiling interrupt
val sigbus : int
Bus error
val sigpoll : int
Pollable event
val sigsys : int
Bad argument to routine
val sigtrap : int
Trace/breakpoint trap
val sigurg : int
Urgent condition on socket
val sigxcpu : int
Timeout in cpu time
val sigxfsz : int
File size limit exceeded
exception Break
Exception raised on interactive interrupt if Sys.catch_break is on.
val catch_break : bool -> unit
catch_break governs whether interactive interrupt (ctrl-C) terminates the program or raises the Break exception. Call catch_break true to enable raising Break, and catch_break false to let the system terminate the program on user interrupt.
val ocaml_version : string
ocaml_version is the version of OCaml. It is a string of the form "major.minor[.patchlevel][+additional-info]", where major, minor, and patchlevel are integers, and additional-info is an arbitrary string. The [.patchlevel] and [+additional-info] parts may be absent.
val enable_runtime_warnings : bool -> unit
Control whether the OCaml runtime system can emit warnings on stderr. Currently, the only supported warning is triggered when a channel created by open_* functions is finalized without being closed. Runtime warnings are enabled by default.
val runtime_warnings_enabled : unit -> bool
Return whether runtime warnings are currently enabled.
Optimization
val opaque_identity : 'a -> 'a
For the purposes of optimization, opaque_identity behaves like an unknown (and thus possibly side-effecting) function.

At runtime, opaque_identity disappears altogether.

A typical use of this function is to prevent pure computations from being optimized away in benchmarking loops. For example: 

      for _round = 1 to 100_000 do
        ignore (Sys.opaque_identity (my_pure_computation ()))
      done