Contents

getkeywords()

Usage:

getkeywords(arg1 [,arg2, arg3 ...]), arg1, arg2, ... arbitrary.

Keywords: syntax, macros

result <- getkeywords(arg1 [, arg2, ..., argK]) returns a CHARACTER
vector of length K.  If argument i is a keyword phrase, result[i] is the
keyword name; otherwise result[i] is "".

  Cmd> getkeywords(cos:3, kappa:PI,a,"b",3)
  (1) "cos"
  (2) "kappa"
  (3) ""
  (4) ""
  (5) ""

The principal use for getkeywords() is in a macro.  It is one of the
tools for analyzing the argument list to a macro.  For example, it is
sometimes necessary to identify which arguments are keyword phrases and
which are not.

Here is a snippet of code that might be in a macro.

  @keynames <- getkeywords($0) # check entire argument list
  @keynames <- @keynames[!ismissing(@keynames)] # extract keyword names
  if (!isnull(@keynames)){
    @legalkeys <- vector("short","long","narrow","wide")
    for (@i,1,length(@keynames)){
      if (match(@keynames[@i], @legalkeys, 0) == 0) {
        error(paste(@keynames[@i],"is not a legal keyword"))
      }
    }
  }

This checks to see that all keywords in the argument list are in a list
of permissible keyword names.

See also argvalue(), keyvalue(), 'keywords', 'macro_syntax', 'macros',
match().