Protect Function and Option Names

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The names of the built-in MuPAD® functions and options are protected. If you try to assign a value to a MuPAD function or option, the system throws an error. This approach ensures that you will not overwrite a built-in function or option accidentally.

If you create a new MuPAD procedure, it is recommended to protect the procedure and all its options, especially if you often use that procedure. For example, MuPAD does not provide a function for computing Lucas numbers. You can write your own procedure for computing Lucas numbers, and then protect the procedure name.

The Lucas numbers are a sequence of integers. The recursion formula that defines the nth Lucas number is similar to the definition of the Fibonacci numbers:

Create the following procedure that computes the nth Lucas number:

lucas:= proc(n:Type::PosInt)
  option remember;
  if n = 1 then
  elif n = 2 then
    lucas(n - 1) + lucas(n - 2)
lucas(i) $ i = 1..5

Now protect the procedure name, lucas, using protect with the ProtectLevelError option:

protect(lucas, ProtectLevelError):

ProtectLevelError lets you set full protection for the identifier. Now, trying to assign any value to lucas results in error:

lucas := 0
Error: Identifier 'lucas' is protected. [_assign]

Alternatively, you can use the ProtectLevelWarning option. In this case, you can still assign a value to the protected identifier, but a warning appears, for example:

protect(lucas, ProtectLevelWarning):

You can assign any value to lucas now, but such assignment triggers a warning:

lucas := 0
Warning: Protected variable 'lucas' is overwritten. [_assign]

For further computations, remove protection from the identifier lucas: