backquote expansion in LW
Espen Vestre
little discovery I just made, and I think newbies that get confused
by certain postings on backquote may find this very helpful:
In LispWorks(**), the backquote expansion of nested backquotes is
done _exactly_ in the order of the definition in the spec, and it's
possible to trace it!
You can do this little experiment at home:
(trace system::backquote-translate)
'`(gazonk `(foo ,(bar ,gazonk)))
(*) Troll follow-ups will be redirected to /dev/null (I promise!) ;-)
(**) tested on LW 4.2.6 linux + win32
--
(espen)
ilias
> I might be feeding the trolls (*), but I couldn't resist posting a
> little discovery I just made, and I think newbies that get confused
> by certain postings on backquote may find this very helpful:
why don't you post in topic, if you care about the newbies?
don't you realize that you behave like a troll?
>
> In LispWorks(**), the backquote expansion of nested backquotes is
> done _exactly_ in the order of the definition in the spec, and it's
> possible to trace it!
>
> You can do this little experiment at home:
>
> (trace system::backquote-translate)
> '`(gazonk `(foo ,(bar ,gazonk)))
>
> (*) Troll follow-ups will be redirected to /dev/null (I promise!) ;-)
> (**) tested on LW 4.2.6 linux + win32
i'm a lisp novice.
function 'trace'
looks very nice.
i'll use it.
in the next document.
here the output of this function:
----------------------------------------------------------------------
CL-USER 1 > (trace system::backquote-translate)
(SYSTEM::BACKQUOTE-TRANSLATE)
0 SYSTEM::BACKQUOTE-TRANSLATE > ((FOO #))
>> SYSTEM::FORM : (FOO (SYSTEM::*BACKQUOTE-COMMA* BAR #))
1 SYSTEM::BACKQUOTE-TRANSLATE > (FOO)
>> SYSTEM::FORM : FOO
1 SYSTEM::BACKQUOTE-TRANSLATE < (QUOTE FOO)
1 SYSTEM::BACKQUOTE-TRANSLATE > ((#))
>> SYSTEM::FORM : ((SYSTEM::*BACKQUOTE-COMMA* BAR #))
2 SYSTEM::BACKQUOTE-TRANSLATE > ((SYSTEM::*BACKQUOTE-COMMA* BAR #))
>> SYSTEM::FORM : (SYSTEM::*BACKQUOTE-COMMA* BAR
(SYSTEM::*BACKQUOTE-COMMA* . GAZONK))
2 SYSTEM::BACKQUOTE-TRANSLATE < (SYSTEM::*BACKQUOTE-COMMA* (BAR #))
2 SYSTEM::BACKQUOTE-TRANSLATE > (NIL)
>> SYSTEM::FORM : NIL
2 SYSTEM::BACKQUOTE-TRANSLATE < (NIL NIL)
1 SYSTEM::BACKQUOTE-TRANSLATE < (LIST (#))
0 SYSTEM::BACKQUOTE-TRANSLATE < (LIST (# #))
0 SYSTEM::BACKQUOTE-TRANSLATE > ((GAZONK #))
>> SYSTEM::FORM : (GAZONK (SYSTEM::BQ-LIST # #))
1 SYSTEM::BACKQUOTE-TRANSLATE > (GAZONK)
>> SYSTEM::FORM : GAZONK
1 SYSTEM::BACKQUOTE-TRANSLATE < (QUOTE GAZONK)
1 SYSTEM::BACKQUOTE-TRANSLATE > ((#))
>> SYSTEM::FORM : ((SYSTEM::BQ-LIST # #))
2 SYSTEM::BACKQUOTE-TRANSLATE > ((SYSTEM::BQ-LIST # #))
>> SYSTEM::FORM : (SYSTEM::BQ-LIST (QUOTE FOO) (BAR #))
3 SYSTEM::BACKQUOTE-TRANSLATE > (SYSTEM::BQ-LIST)
>> SYSTEM::FORM : SYSTEM::BQ-LIST
3 SYSTEM::BACKQUOTE-TRANSLATE < (QUOTE SYSTEM::BQ-LIST)
3 SYSTEM::BACKQUOTE-TRANSLATE > ((# #))
>> SYSTEM::FORM : ((QUOTE FOO) (BAR #))
4 SYSTEM::BACKQUOTE-TRANSLATE > ((QUOTE FOO))
>> SYSTEM::FORM : (QUOTE FOO)
5 SYSTEM::BACKQUOTE-TRANSLATE > (QUOTE)
>> SYSTEM::FORM : QUOTE
5 SYSTEM::BACKQUOTE-TRANSLATE < (QUOTE QUOTE)
5 SYSTEM::BACKQUOTE-TRANSLATE > ((FOO))
>> SYSTEM::FORM : (FOO)
6 SYSTEM::BACKQUOTE-TRANSLATE > (FOO)
>> SYSTEM::FORM : FOO
6 SYSTEM::BACKQUOTE-TRANSLATE < (QUOTE FOO)
6 SYSTEM::BACKQUOTE-TRANSLATE > (NIL)
>> SYSTEM::FORM : NIL
6 SYSTEM::BACKQUOTE-TRANSLATE < (NIL NIL)
5 SYSTEM::BACKQUOTE-TRANSLATE < (QUOTE (FOO))
4 SYSTEM::BACKQUOTE-TRANSLATE < (QUOTE (QUOTE FOO))
4 SYSTEM::BACKQUOTE-TRANSLATE > ((#))
>> SYSTEM::FORM : ((BAR #))
5 SYSTEM::BACKQUOTE-TRANSLATE > ((BAR #))
>> SYSTEM::FORM : (BAR (SYSTEM::*BACKQUOTE-COMMA* . GAZONK))
6 SYSTEM::BACKQUOTE-TRANSLATE > (BAR)
>> SYSTEM::FORM : BAR
6 SYSTEM::BACKQUOTE-TRANSLATE < (QUOTE BAR)
6 SYSTEM::BACKQUOTE-TRANSLATE > ((#))
>> SYSTEM::FORM : ((SYSTEM::*BACKQUOTE-COMMA* . GAZONK))
7 SYSTEM::BACKQUOTE-TRANSLATE >
((SYSTEM::*BACKQUOTE-COMMA* . GAZONK))
>> SYSTEM::FORM : (SYSTEM::*BACKQUOTE-COMMA* . GAZONK)
7 SYSTEM::BACKQUOTE-TRANSLATE <
(SYSTEM::*BACKQUOTE-COMMA* GAZONK)
7 SYSTEM::BACKQUOTE-TRANSLATE > (NIL)
>> SYSTEM::FORM : NIL
7 SYSTEM::BACKQUOTE-TRANSLATE < (NIL NIL)
6 SYSTEM::BACKQUOTE-TRANSLATE < (LIST (GAZONK))
5 SYSTEM::BACKQUOTE-TRANSLATE < (LIST (# GAZONK))
5 SYSTEM::BACKQUOTE-TRANSLATE > (NIL)
>> SYSTEM::FORM : NIL
5 SYSTEM::BACKQUOTE-TRANSLATE < (NIL NIL)
4 SYSTEM::BACKQUOTE-TRANSLATE < (LIST (#))
3 SYSTEM::BACKQUOTE-TRANSLATE < (LIST (# #))
2 SYSTEM::BACKQUOTE-TRANSLATE < (LIST (# # #))
2 SYSTEM::BACKQUOTE-TRANSLATE > (NIL)
>> SYSTEM::FORM : NIL
2 SYSTEM::BACKQUOTE-TRANSLATE < (NIL NIL)
1 SYSTEM::BACKQUOTE-TRANSLATE < (LIST (#))
0 SYSTEM::BACKQUOTE-TRANSLATE < (LIST (# #))
CL-USER 2 > '`(gazonk `(foo ,(bar ,gazonk)))
(SYSTEM::BQ-LIST (QUOTE GAZONK) (SYSTEM::BQ-LIST (QUOTE SYSTEM::BQ-LIST)
(QUOTE (QUOTE FOO)) (SYSTEM::BQ-LIST (QUOTE BAR) GAZONK)))
CL-USER 3 >
ilias
well, i've played a little with this.
and i'm now *really* confused.
why do you give me the best argument, that the definition of backquote
is wrong?
anyway.
ilias
now what you've provided is irrelevant.
it describes internal implementation-dependent processing.
the specs state 'expanded', expansion referes to replacing ` with the
implementation-dependent function and , with the
implementation-dependent function(s), thus creating the evaluateable
representation of the input-string.
in LispWorks:
CL-USER 1 > (get-macro-character #\`)
SYSTEM::READ-BACKQUOTE
NIL
thus you should simply trace this:
(trace System::read-backquote)
test expression:
`(,a `(,,b))
and the you got what's obvious:
(i've abbreviated some text, so the lines fit in one line.
0 SYSTEM::READ-BACKQUOTE > (#<E::RS #<EDITOR... i-pane 2>> #\`)
>> STREAM : #<E::RS #<EDITOR... i-pane 2>>
>> CHAR : #\`
1 SYSTEM::READ-BACKQUOTE > (#<E::RS #<EDITOR... i-pane 2>> #\`)
>> STREAM : ##<E::RS #<EDITOR... i-pane 2>>
>> CHAR : #\`
1 SYSTEM::READ-BACKQUOTE < ((SYSTEM::BQ-LIST #))
0 SYSTEM::READ-BACKQUOTE < ((SYSTEM::BQ-LIST A #))
CL-USER 7 > `(,a `(,,b))
| |
0-----------+ |
1--------------+
outermost backquote is expanded first.
thus: specs paragraph 'nested backquote' wrong.