I tried today to make a case that used variables instead of constants and was surprised to get an error. I’m sure this been true since the 80’s but why don’t cases allow variables??? I thought a case statement was just a group of if..else blocks in succession.

Regards,
Ryan Joseph

Ryan Joseph schrieb am Mo., 29. Okt. 2018,
10:41:

No it's not. At least for ordinal values it's usually implemented as a jump table or something optimized like that which would not work with variables as labels.

Regards,
Sven

I tried today to make a case that used variables instead of constants and was surprised to get an error. I’m sure this been true since the 80’s but why don’t cases allow variables??? I thought a case statement was just a group of if..else blocks in succession.

Case has never allowed variables.

and it is also not a group of if..else blocks. The compiler uses jump tables when possible etc when it encounters a case.

Michael.

I think it is important to differentiate between a language feature and its common implementation. Perhaps case statements with variables make sense? Of course, that doesn't mean anyone is going to add them.

I suggest the OP look up pattern matching. Scala may be more readable than Haskell, and there is also OCaml.

Cheers,
R0b0t1

R0b0t1 wrote

I think it is important to differentiate between a language feature and its common implementation. Perhaps case statements with variables make sense? Of course, that doesn't mean anyone is going to add them.

"case" also includes a compile time check, that case-labels have no duplicates.

Therefore using variables in place of case labels, would require changes to the definition of what case does.

I’ve been programming Pascal since about 1995 and I never knew cases were an optimization or had any special meaning. In my mind I thought they were just a nice way to do branching when there were lots of cases to check (hence the “case statement”).

Under the hood I would think cases with variables should just perform as if..else statements but as was pointed out that would require a significant amount of work.

Just wanted to make sure I wasn’t going crazy because you’d think a person like me would know something so basic about Pascal by now.

Regards,
Ryan Joseph

In our previous episode, Ryan Joseph said:

It is just like a for loop is not exactly like a naieve while loop because the bounds are only evaluated once. Some details you only acquire as very experienced programmer, or implementator.