Disabling Functions in Student Answers

This shows how to disable functions allowed in student answers.

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Complete Code

Download file: DisableFunctions.pg

PG problem file

Explanation

DOCUMENT();
loadMacros('PGstandard.pl', 'PGML.pl', 'PGcourse.pl');

Preamble

These standard macros need to be loaded. 
# Disable exponents in the context.
Context()->operators->undefine('^', '**');

# Disable the 'sin', 'cos', 'tan', 'abs', and 'sqrt' functions.
Context()->functions->undefine('sin', 'cos', 'tan', 'abs', 'sqrt');

# Remove the '|' parenthesis operator which starts and ends an absolute value.
# This needs to be done in addition to disabling the 'abs' function to fully
# disable absolute values.
Context()->parens->remove('|');

# Give consistent error messages if the '|' absolute value parenthesis operator
# is attempted to be used by the student.
Context()->{error}{convert} = sub {
    my $message = shift;
    $message =~ s/Unexpected character '~~|'/Absolute value is not allowed/;
    return $message;
};

$ans = Compute('1/2');

Setup

Specific operations in the context can be disabled with Context()->operations->undefine. The predefined operations are * (multiplication), / (division), + (addition), - (subtraction), ! (factorial), >< (cross product), U (union), ^ (exponent), ** (exponent), . (dot product), and , (list creation).

After disabling an operation, it can be re-enabled with Context()->operators->redefine, e.g., Context()->operators->redefine('^').

Operators can be removed from the context with Context()->operators->remove, but this is not recommended as it makes it completely unknown in the context so that students will not get helpful error messages if they try to use them.

Specific functions can be disabled in the context with Context()->functions->undefine. The predefined functions are sin, cos, tan, sec, csc, cot, asin, acos, atan, asec, acsc, acot, sinh, cosh, tanh, sech, csch, coth, asinh, acosh, atanh, asech, csch, acoth, ln, log, log10, exp, sqrt, abs, int, sgn, atan2, norm, unit, arg, mod, Re, Im, and conj.

In addition, classes of functions can be disabled by passing one of the following arguments to Context()->functions->disable:

  • Trig: disables all trig functions listed in both SimpleTrig and InverseTrig functions
  • SimpleTrig: disables sin, cos, tan, sec, csc, cot
  • InverseTrig: disables asin, acos, atan, asec, acsc, acot, atan2
  • Hyperbolic: disables all hyperbolic functions in both SimpleHyperbolic and InverseHyperbolic functions
  • SimpleHyperbolic: disables sinh, cosh, tanh, sech, csch, coth
  • InverseHyperbolic: disables asinh, acosh, atanh, asech, acsch, acoth
  • Numeric: disables ln, log, log10, exp, sqrt, abs, int, sgn
  • Vector: disables norm, unit
  • Complex: disables arg, mod, Re, Im, conj
  • All: diables all predefined functions

Alternatively, the following syntax can be used.

Parser::Context::Functions::Disable('All');
BEGIN_PGML
Find the numerical value: [`\sin^2(\pi / 4) =`] [____]{$ans}
END_PGML

Statement

This is the problem statement in PGML. 
BEGIN_PGML_SOLUTION
Solution explanation goes here.
END_PGML_SOLUTION

ENDDOCUMENT();

Solution

A solution should be provided here.