theory ExternalSolver
imports "../Appendix"
begin


section {* Executing an External Application (TBD) \label{rec:external}*}

text {*
  {\bf Problem:}
  You want to use an external application.
  \smallskip

  {\bf Solution:} The function @{ML system_out} might be the right thing for
  you.
  \smallskip

  This function executes an external command as if printed in a shell. It
  returns the output of the program and its return value.

  For example, consider running an ordinary shell commands:

  @{ML_response [display,gray] 
    "system_out \"echo Hello world!\"" "(\"Hello world!\\n\", 0)"}

  Note that it works also fine with timeouts (see Recipe~\ref{rec:timeout}
  on Page~\pageref{rec:timeout}), i.e. external applications are killed
  properly. For example, the following expression takes only approximately
  one second:

  @{ML_response_fake [display,gray] 
    "TimeLimit.timeLimit (Time.fromSeconds 1) system_out \"sleep 30\"
     handle TimeLimit.TimeOut => (\"timeout\", ~1)" "(\"timeout\", ~1)"}

  The function @{ML system_out} can also be used for more reasonable
  applications, e.g. coupling external solvers with Isabelle. In that case,
  one has to make sure that Isabelle can find the particular executable.
  One way to ensure this is by adding a Bash-like variable binding into
  one of Isabelle's settings file (prefer the user settings file usually to
  be found at @{text "$HOME/.isabelle/etc/settings"}).
  
  For example, assume you want to use the application @{text foo} which
  is here supposed to be located at @{text "/usr/local/bin/"}.
  The following line has to be added to one of Isabelle's settings file:

  @{text "FOO=/usr/local/bin/foo"}

  In Isabelle, this application may now be executed by

  @{ML_response_fake [display,gray] "system_out \"$FOO\"" "\<dots>"}
*}


end