% -*- mode: Noweb; noweb-code-mode: caml-mode -*-
% $Id: option.nw,v 1.6 2004-06-05 15:35:48 govereau Exp $
\section{Command Line Options}
\label{sec:options}

% ---------------------------------------------------------------------------
\subsection{Options}
% ---------------------------------------------------------------------------
The [[Option]] module provides command line parsing and access to
option settings. On startup, the [[parse_cmdline]] function parses the
command line and stores the state of all user settable options. Other
modules may access the value of options through the accessor
functions.
<<option.mli>>=
val parse_cmdline : unit -> unit
val print_ast     : unit -> bool
val print_ext     : unit -> bool
val print_lext    : unit -> bool
val use_unwind    : unit -> bool
val filename      : unit -> string
val channel       : unit -> in_channel
@
% ---------------------------------------------------------------------------
\subsection{Option Implementation}
% ---------------------------------------------------------------------------
Each parameter is kept in a private variable, and the accessor
functions simply return the values of these variables.
<<option.ml>>=
let ast    = ref false
let ext    = ref false
let lext   = ref false
let unwind = ref false
let file   = ref ""
let inch   = ref stdin

let print_ast()  = !ast
let print_ext()  = !ext
let print_lext() = !lext
let use_unwind() = !unwind
let filename()   = !file
let channel()    = !inch
@
When an input file is specified by the user, the [[set_input]]
function is called.
<<option.ml>>=
let set_input s =
  try file := s; inch := open_in s
  with Sys_error err ->
    raise (Arg.Bad ("could not open file " ^ err))
@
The command line is processed using the [[Arg]] module from the Ocaml
standard library. First we define a set of option specs, and then call
the [[Arg]] module. After processing, we check the options for
consistency.
<<option.ml>>=
let rec usage() = Arg.usage options "Usage:";exit 0;
and options = [
  "-ast",      Arg.Set ast,    "\t\tprint Abstract Syntax Tree";
  "-ext",      Arg.Set ext,    "\t\tprint Expression Trees";
  "-lext",     Arg.Set lext,   "\tprint Linearized Expression Trees";
  "-unwind",   Arg.Set unwind, "\tuse unwind continuations for exceptions";
  "-help",     Arg.Unit usage, "\tprint this message";
]
let parse_cmdline() = Arg.parse options set_input "Usage:"
@