Example:
Write a function which returns number passed into it as an argument.
Solution:
f=x=>x
What is its length?
Is it 4 as a length of the lambda x=>x only or 6 as a length of whole statement with assignment?
What if there are 2 functions?
g=x=>x/2
f=x=>g(x)+g(x)
Unless the challenge explicitly asks for a named function unnamed functions are completely legitimate. That means you don't count the assignment either. So your example
f=x=>x
would be four bytes, and I wouldn't even include f= in the post, so that it's clear how I've counted.
What if there are two functions? That depends. If the questions actually asks for two functions (e.g. a decoder and an encoder), count them separately just like you would count a single function. This means that neither assignment would be counted. For instance, if your two submissions were
f=x=>x*x
g=x=>sqrt(x)
I'd count that as 6 + 10 = 16. Again I would not actually write f= and g= in the post.
However, if you define one function to be used in another, like you did in your example, then the first assignment definitely needs to be counted. Your f wouldn't work without the assignment, because it references g by name. So I would count the assignment to g but not the assignment to f. I would present the solution like this:
g=x=>x/2
x=>g(x)+g(x)
and therefore count it as 21 bytes.
Likewise, if a function is recursive, you must also count the assignment:
f=x=>x&&f(x-1)
Would count as 14 bytes since the function wouldn't work unless f was defined.
The length of the lambda is the same as with a full program: the length of your function is the number of characters including the assignment. You want something that can be inserted as a line, not proceeding or preceding any other code on that line.
So, in Python:
f=lambda x:x*2
Is 14 bytes and:
f=lambda x:x*2
g=lambda y:y*3
is 29 bytes.
This is akin to the language handicaps: keep it simple and easy to police.
lambda x:x*2 is 12.
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