Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.compilers > #3019

Re: Who first invented dotted-item notation?

Show all headers | View raw

On 2022-05-22, Christopher F Clark <christopher.f.clark@compiler-resources.com> wrote:
> I know the notation from LR(0) machine construction, but also know
> that Gluskhov used it in his solution to NFA construction.  Earley
> also used the notation to describe his method if I understand right.
> I'm presuming that there is some first use of the notation.  Do we
> know who invented it?

In Lisp, we can write (1 2 3 4 5 6) in any of these ways:

(1 . (2 3 4 5 6))
(1 2 . (3 4.5 6))
(1 2 3 . (4 5 6))
(1 2 3 4 . (5 6))
(1 2 3 4 5 . (6))
(1 2 3 4 5 6 . NIL)

As well as:

(1 . (2 . (3 4 5 6)))

The dot doesn't actually exist; it isn't represented anywhere in the
data structure, but in a hand-written expression it could be used to
convey (purely as a comment) some semanticaly interesting division in
the list.

E.g. suppose we have some data structure which holds a list of symbols,
and an integer indicating a position among those symbols.

A custom printing routine for that structure could take advantage
of this, rendering it as, say:

  #S(sym-structure
    :dot-position 2
    :syms (a b . (c d)))

where the custom printer for sym-structure looks at dot-position
and renders the syms slot accordingly, to provide a visual aid.

The following is not possible in any mainstream Lisp I know of: (. (a b c))
as a way of denoting (a b c).  The custom printer could omit the
dot notation.

(I know of a dialect in which it that leading dot notation is allowed,
with that semantics, but starting in a git commit made in 2014, making
it irrelevant here.)

--
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal

Back to comp.compilers | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

Who first invented dotted-item notation? Christopher F Clark <christopher.f.clark@compiler-resources.com> - 2022-05-22 12:32 +0300
  Re: Who first invented dotted-item notation? Kaz Kylheku <480-992-1380@kylheku.com> - 2022-05-22 18:29 +0000
    RE: Who first invented dotted-item notation? Christopher F Clark <christopher.f.clark@compiler-resources.com> - 2022-05-23 13:23 +0300
  Re: Who first invented dotted-item notation? gah4 <gah4@u.washington.edu> - 2022-05-23 18:31 -0700
    RE: Who first invented dotted-item notation? Christopher F Clark <christopher.f.clark@compiler-resources.com> - 2022-05-24 11:27 +0300
      Re: Who first invented dotted-item notation? antispam@math.uni.wroc.pl - 2022-05-28 04:51 +0000

csiph-web