Edit history: 2004-06-10, Version 1 by Lars Brinkhoff
Status: For CLiki consideration
- Problem Description:
- The description of BUTLAST and NBUTLAST isn't self-consistent when applied to dotted list.
- Proposal (BUTLAST-DOTTED-LIST:OMIT-CONSES):
- The specified number of cons cells at the end of the list should be removed.
- Proposal (BUTLAST-DOTTED-LIST:RPLACD-TO-NIL):
- Set the cdr of the cons n+1 from the end of the list to nil.
- Test case:
- (butlast '(a b . c) 0)
- Mostly this precludes implementations from arbitraily adopting one of the two possible interpretations.
- Current practice:
- (butlast '(a b . c) 0) returns (a b) in CLISP 2.32 and CMUCL release-18e-branch but (a b . c) in SBCL 0.8.9.46.
- Cost to Implementors:
- Cost to Users:
- None. Portable programs cannot currently rely on any particular behavior.
- Cost of Non-Adoption:
- Users would be confused about what to expect because implementations might implement either of the two behaviours.
- Tighter spec.