(* Unix -- SML Basis Library *) type proctype signal = Signal.signal val executeInEnv : string * string list * string list -> proc val execute      : string * string list -> proc val streamsOf    : proc -> TextIO.instream * TextIO.outstreamval kill         : proc * signal -> unitval reap         : proc -> Process.status  (*    This structure allows Moscow ML programs to start other processes   and to communicate with them.      Child processes are not automatically terminated when the parent   (ML) process terminates.  To forcibly terminate a child process pr,   use Unix.kill(pr, Signal.term).  Then, to remove the terminated   process from the operating system tables, call Unix.reap(pr).    The protocol for communication between the ML program and its child   process must be designed with some care, typically using   non-blocking input for reading from the child process.    [proc] is the type of processes started by the ML program.    [signal] is the type of Unix-style signals, which can be sent to   another process.  Signal values must be obtained from the Signal   structure.    [execute (cmd, args)] asks the operating system to execute the   command cmd with the argument list args, as a separate process.   Two pipes connected to the standard input and standard output of   the new process are created; these may be obtained using streamsOf.   A proc value representing the new process is returned.  The new   process executes using the same environment as the calling process.   Raises Fail in case of failure, e.g. if the process or the pipes   cannot be created.    Typically, the cmd argument will be the full pathname of an   executable.  On Unix systems, simple command searching as done by   the shell, allowing cmd to be a relative pathname, can be achieved   by using        execute("/bin/sh", "-c" :: concat (cmd :: " " :: args))    [executeInEnv (cmd, args, env)] asks the operating system to   execute the command cmd with the argument list args in the   environment env, as a separate process.  Returns a proc value   representing the new process.  Typically, a string in the env list   has the form "NAME=VALUE".  See also Process.getEnv.      [streamsOf pr] returns a pair (ins, outs) of input and output   streams associated with process pr.  The standard output of pr is   the source for the input stream ins, and the standard input of pr   is the sink for the output stream outs.    [reap pr] closes the input and output streams associated with pr,   and then suspends the current (ML) process until the process   corresponding to pr terminates.  Returns the exit status given by   pr when it terminated.  Raises Fail in case of failure, e.g. if pr   has already been reaped.    Under Unix, information about a terminated process remains in the   system tables until the process is reaped.  Thus, an ML program   using execute or executeInEnv must make sure to reap any process it   has created, or else the system tables will fill up.    [kill (pr, s)] sends the signal s to the process pr.  Raises Fail   in case of failure, e.g. if pr has already been killed.*)