Backquote bug

[DanielAjoy]

I'm reading the UCBLogo user manual:

Backquotes can be nested. Substitution is done only for commas at the same depth as the backquote in which they are found:

SHOW `[a `[b ,[1+2] ,[foo ,[1+3] d] e] f]
[a ` [b , [1+2] , [foo 4 d] e] f]

It seems to me that only the inner most comma was resolved, which was not at the same depth as the backquotes.

[brianharvey]

The language may be unclear, but this is the correct behavior. After the [a [b we're two levels deep in backquotes. The ,[1+2] is just one level of comma, same with the ,[foo ...]. But the ,[1+3] is two commas deep, matching the two backquotes deep. (Good timing, though -- I'm just implementing backquote for Snap!.)

[DanielAjoy]

Is the single backquote in the result after the "a" supposed to be there?

[brianharvey]

Yup! From the Scheme manual: