##########################################################
#
#  Example showing how to add a new single-variable function to the Parser
#

DOCUMENT();        # This should be the first executable line in the problem.

loadMacros(
  "PGbasicmacros.pl",
  "PGanswermacros.pl",
  "Parser.pl",
  "parserTables.pl",
);

TEXT(beginproblem());

###########################################################
#
#   Use  standard numeric mode
#
Context('Numeric');

#############################################
#
#  Create a 'log2' function to the Parser for log base 2
#

package MyFunction1;
our @ISA = qw(Parser::Function::numeric); # this is what makes it R -> R

sub log2 {
  shift; my $x = shift;
  return CORE::log($x)/CORE::log(2);
}

package main;

#
#  Make it work on formulas as well as numbers
#
sub log2 {Parser::Function->call('log2',@_)}

#
#  Add the new functions into the Parser
#

Context()->functions->add(
  log2 => {class => 'MyFunction1', TeX => '\log_2'},  # fancier TeX output
);

$x = Formula('x');

###########################################################
#
#  The problem text
#
BEGIN_TEXT
$BEGIN_ONE_COLUMN

In this problem, we have added a new function to the Parser: ${BTT}log2(x)${ETT}.
(Edit the code to see how this is done.)
$PAR
Assuming that ${BTT}${DOLLAR}x = Formula('x')${ETT}, it can be used as follows:
$PAR

\{ParserTable(
     'Formula("log2(x)")',
     'log2(8)',
     'log2($x+1)',
     'Formula("log2(x)")->eval(x=>16)',
     '(log2($x))->eval(x=>16)',
     'Formula("log2()")',
     'Formula("log2(1,x)")',
     'log2()',
     'log2(1,3)',
  )\}

$END_ONE_COLUMN
END_TEXT

###########################################################

ENDDOCUMENT();        # This should be the last executable line in the problem.