toke.c: S_intuit_more: Add more commentary #23708
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This function is described in its comments as 'terrifying', and by its original author, Larry Wall, as "truly awful". As a result, it has been mostly untouched since its introduction in 1993. That means it has not been updated as new language features have been added. As an example, it does not know about lexical variables, so the code it has for globals just doesn't work on the vast majority of modern day coding practices. Another example is it knows nothing of UTF-8, and as a result simply changing the input encoding from Latin1 to UTF-8 can result in its outcome being the opposite result. And it is buggy. An example of how hard this can be to get right is this fairly common use in our test suite: [$A-Z] That looks like a character class matching 27 characters. But wait, what if there exists a $A and a parameterless subroutine 'Z'. Then this could instead be an expression for a subcript. A few years ago, I set out to try to understand it. I added commentary and simplified some overly complicated expressions, but left its behavior unchanged. Now, I set out to make some changes, and found many more issues than I had earlier. This commit adds commentary about those. Hopefully this will lead to some discussion and a consensus on the way forward.
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This function is described in its comments as 'terrifying', and by its original author, Larry Wall, as "truly awful". As a result, it has been mostly untouched since its introduction in 1993. That means it has not been updated as new language features have been added.
As an example, it does not know about lexical variables, so the code it has for globals just doesn't work on the vast majority of modern day coding practices.
Another example is it knows nothing of UTF-8, and as a result simply changing the input encoding from Latin1 to UTF-8 can result in its outcome being the opposite result.
And it is buggy.
A few years ago, I set out to try to understand it. I added commentary and simplified some overly complicated expressions, but left its behavior unchanged.
Now, I set out to make some changes, and found many more issues than I had earlier. This commit adds commentary about those. Hopefully this will lead to some discussion and a consensus on the way forward.