There is no such thing as an undefined value and there is certainly no such thing as a numeric context

Actually, even strongly typed languages have a numeric context - and other contexts. In strongly typed languages like Go, the context is used (at compile time) to enforce that a variable or value of a specific type is used.

Also, being strongly typed does not automatically exclude the concept of "undefined value". "undefined" is a sentinel that is reserved and predefined by the language. Many "purists" mistakenly equate undefined with uninitialized. While uninitialized implies undefined, the reverse need not be true. Like "NaN" (not a number) is useful, having undefined as a reserved, predefined representation of a sentinel can also be useful. Otherwise, you have to decide on a value to use as a sentinel, then hope that value never appears in your data.*

Unfortunately, the way Perl uses undefined contributes to the confusion between uninitialized and undefined. It would have been better for Perl to have a flag for uninitialized as well as undefined. At least Perl has a test for undefined. Off hand, I don't recall any other languages that provide a test for undefined.

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* While NaN could be used as a sentinel, it's mathematical definition is an unrepresentable value, which is different from an undefined value.