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Error Message Customization

This PG code shows how to customize (remap) the error messages students receive after submitting an incorrect response or making a syntax error when entering their answer. This requires using MathObjects or a macro file that loads MathObjects, so that a Context is defined.

You may also be interested in AnswerHints

Problem Techniques Index

PG problem file Explanation

Initialization: To be able to customize the error messages students receive, we must be using MathObjects or a macro that loads MathObjects and has a Context.

Context()->{error}{msg}{"Missing operand after '-'"} 
  = "Enter '-1' instead of '-'";

$ans1 = Real(-1);
$ans2 = Formula("x-2");

Setup: First, specify a Context. One way to remap the error message is through the context. In factoring -x+2 as -(x-2), students may enter - instead of -1 in the first answer box and receive the error message Missing operand after '-'. We can replace this error message with "Enter '-1' instead of '-'" via the Context()->{error}{msg}... code to the left. The replacement error message can be anything you like as long as it is nonempty. To generate a blank error message, use a quoted space " ", not "".

For another way to customize the error message, see the Answer Evaluation section below.

Factor \( -1 \) from \( -x+2 \).
\( -x + 2 = \) 
\{ ans_rule(5) \} 
\( \cdot \big( \) 
\{ ans_rule(10) \} 
\( \big) \)

Main Text: The problem text section of the file is as we'd expect.

ANS( $ans1->cmp() );
ANS( $ans2->cmp() );


Answer Evaluation: Another way to customize the error message Missing operand after '-' would be to use a post-filter to remove the message after the answer has been graded. The macro provides one way to do this, but it is probably just as easy to do it manually, as in:

ANS($ans1->cmp->withPostFilter(sub { 
  my $ans = shift; 
  $ans->{ans_message} = "Enter '-1' instead of '-'" 
    if $ans->{ans_message} eq "Missing operand after '-'";
  return $ans; 

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