## WeBWorK Problems

### Re: Does a method exist to say whether or not a Formula uses a given function?

by Davide Cervone -
Number of replies: 0

It turns out this is easier than I thought. Here is a little code that does the trick:

package my::Function;
our @ISA = ('Parser::Function');

sub new {
my $self = shift; my ($equation, $name) = @_;$equation->{functions}{$name} = 1;$self->SUPER::new(@_);
}

package main;

Context("Numeric")->{parser}{Function} = 'my::Function';

$f = Formula("sin(x+sqrt(x+1))"); TEXT(join(', ', keys %{$f->{functions} || {}}));


This subclasses the Parser::Function object and overrides the new method so that it marks the names of the functions used in the formula. You could use $f->{functions}{sqrt} to determine if sqrt() had been used in the formula. Note that if you use Compute() rather than Formula(), and the result is a constant, you won't get the functions property because the formula will have been evaluated to the constant, but you can use $f->{equation}{formula} in that case. In an answer checker, you should be able to use $ansHash->{student_value} rather than $ansHash->{student_answer} to access the formula.