AC_PATH_PROG behaviour

[Al]

Ive been working on the simple macro below. The probem is that
AC_PATH_PROG(_MATLAB, matlab$EXEEXT, none) launches Matlab! Configuration is
blocked until Matlab is killed. This isnt right is it? AC_PATH_PROG shouldnt
be launching an executable in the process of finding it. If not, what have I
done wrong? If so, whats the solution that avoids the launch.

dnl Sets MATLAB to Matlab top directory
dnl
dnl May be overridden by defining MATLAB at the configure level.
dnl Note: Only WARNS if Matlab is not located.
dnl
dnl This file is in the PUBLIC DOMAIN
dnl
AC_DEFUN([AC_PATH_MATLAB],[
if test "x$MATLAB" = x; then
    AC_PATH_PROG(_MATLAB, matlab$EXEEXT, none)
    if test "x$_MATLAB" = xnone; then
            AC_MSG_WARN([Matlab not found in $PATH])
    else
        MATLAB="$_MATLAB/../.."
    fi;dnl
fi;dnl
])


Thanks.