Handling math errors in Wipple

Originally posted on wipple.org.

Previously, Wipple’s built-in math operations like / and sqrt would cause the program to crash if provided an invalid input. This caused problems when graphing functions using the math library:

plot (x -> 1 / x) -- crashed when x = 0!

Really, what we want is to skip graphing any points that produce an undefined result. So now, Wipple’s Number type has a new member — undefined!

Rather than crashing, all of Wipple’s math operations now return undefined if provided an invalid or undefined input. This means undefined propagates through the program:

x : sqrt -1
show x -- undefined
show (x + 1) -- undefined

When comparing undefined with another number, the result is always False. If you need to check whether an number is undefined, you can use undefined?:

x : 0 / 0
show (x = undefined) -- False
show (undefined? x) -- True

This behavior matches the NaN value in the IEEE 754 floating-point standard (Wipple’s Number type has a decimal representation, however), and indeed undefined is represented as NaN in JavaScript.