Errors

Now that you've learned the basics in Wall, you can already to a fair bit of exploring. While exploring, if you're anything like everyone else, you will surely run into errors.

The three main errors in Wall are NotAFunctionError, CannotReassignError and IncorrectDomainError.

Not a function

Wall will throw a NotAFunctionError if a value that is not a function, or a value that may not be a function, is invoked as a function

w> 1 2
NotAFunctionError. `1` is or may not be a function.
w> {1: 2, 3: 4 } 1
2
w> good = (? (< rand 0.5) {1: 2} {1: 42})
w> good 1
42 // also could be 2 depending on the outcome of rand
w> bad = (? (< rand 0.5) {1: 2} 1)
w> bad 1
NotAFunctionError. `bad` is or may not be a function.

Cannot reassign

We saw in the Assignment section that a symbol cannot be reassigned.

w> stacy fred = 
w> stacy = fred
CannotReassignError. `stacy` cannot be reassigned.

Incorrect domain

An incorrect domain error is raised when a function is called with a value that is or may not be in the domain of the function.

w> { 2: 3 } 4
IncorrectDomainError. The function `{ 2: 3 }` does not or may not contain the element `4` in its domain.
w> good = (? (< rand 0.5) {1: 2} {1: 42})
w> good 1
42 // also could be 2 depending on the outcome of rand
w> bad = (? (< rand 0.5) {1: 2} {2 :5})
w> bad 1
IncorrectDomainError. The function `bad` does not or may not contain the element `1` in its domain.