On 7-May-09, at 3:06 AM, lowly coder wrote:
Let's see how much of this I can understand.
- FILE & LINE are macros.
Yes.
- in (lambda (src <-- this variable here the src is linked to the reader/parser object, which is why we
can query it for the current line / file number?
Yes. The parameter is the "source object" corresponding to the macro call. What is a source object? Here's a simple way to find out how source objects are represented:
bash-3.2$ gsi Gambit v4.4.3
(define x #f) (##define-syntax foo (lambda (src) (set! x src) '(begin))) (foo (stuff) turkey) x
#(#(source1) (#(#(source1) foo (console) 65538) #(#(source1) (#(#(source1) stuff (console) 393218)) (console) 327682) #(#(source1) turkey (console) 851970)) (console) 2)
(##source? x)
#t
(##source-locat x)
#((console) 2)
(##source-code x)
(#(#(source1) foo (console) 65538) #(#(source1) (#(#(source1) stuff (console) 393218)) (console) 327682) #(#(source1) turkey (console) 851970))
(length (##source-code x))
3
(##source-code (car (##source-code x)))
foo
(##source-code (car (##source-code (cadr (##source-code x)))))
stuff
(##desourcify x)
(foo (stuff) turkey)
(##locat-container (##source-locat x))
(console)
(##locat-position (##source-locat x))
2
(##display-locat (##source-locat x) #t (current-output-port))
(console)@3.1
- Why the ##'s
All the ## names refer to internal functionality that should be used with great care, and is not meant for use by a casual user. The procedures typically don't do any type checking and the API may change at any point. The ## stresses these point in several ways:
1) It is easy to spot in code, so a simple "grep '##' *.scm" will find places in your code that are possibly unsafe or brittle (over versions of Gambit).
2) The ## prefix is "ugly" and may be a deterrent to using these names.
3) The "##" prefix on symbols is illegal in Scheme, so it is clear that by using these names you are definitely non-portable to other Schemes (it turns out that Chicken Scheme supports this extension, so ## is not completely non-portable anymore).
Marc