This code was defined for “I can’t find a function named this”, but nothing in the compiler ever produced it: a call to a function Turf doesn’t know has always been reported as E041 (“Unknown function”). The number is kept so an old log that mentions it still has somewhere to land, and is never reused.
Example
mut n: int = lenght("hello"); // misspelled -- E041, with a "did you mean" suggestionRun turf --explain E041 for the explanation. In short: check the spelling, and check that you have imported the module the function lives in.
Run turf --explain E037 in a terminal to read this again.