<dadinn>so if i have a pattern (foo bar bar* ...) , and i call the macro with (foo 1 2 3 4), then what does bar and bar* bind to? <erkin>bar binds to 1, bar* binds to 2 3 4 <erkin>bar* is not a list, mind you. It's literally multiple syntactic elements at once. <erkin>It might make things easier to consider the template system a separate, Scheme-based DSL than Scheme itself. <erkin>Had you defined it as (foo bar . bar*), bar* would be (2 3 4), merely a list. <dadinn>ok,then i clearly don't understand :) <erkin>... makes it very easy to write recursive macros where you have two templates: (foo bar) and (foo bar bar* ...). If the cdr of the form has only one element, it matches the first template. Otherwise, it falls back to the next one. <erkin>In the (foo bar bar* ...) clause, you can recurse on the macro as (foo bar* ...) to call it again with the rest of the forms given. <erkin>Until only one element remains, then it can match the first (foo bar) clause. <erkin>You can also write mutually recursive macros similarly. <dadinn>so when ... is used in the template it is like ,@ ? <erkin>I wouldn't say so, because ,@foo expands *from* a list foo, whereas foo ... was never a list in the first place. <erkin>It's literally everything the parser matches. ***hugh_marera_ is now known as hugh_marera
<dadinn>so you would recommend I should stick with the cons form instead? <erkin>If it does what you want, yes. It's much easier to deal with. <erkin>I need to go to sleep now. I hope I managed to help you. <erkin>I do agree that there needs to be more newbie-friendly tutorials for Scheme's macro systems (there are seven different ones in use today, across separate implementations, although everyone uses `syntax-rules' for nearly everything). <erkin>I was writing a tutorial myself but got sidelined by work and such. :-P <dadinn>one more question, how does syntax-rules save me from something like: (let ((with-output-to-file (lambda (path) (error "Called the wrong one" path)))) (with-my-output-to-file "test.txt" (display "foobar"))) <erkin>Not sure I get the question. <dadinn>i've noticed on the tree-il it says (toplevel with-output-to-file) but I don't understand <erkin>Yes, at expansion time, the `with-output-to-file' in `let' bindings is a separate symbol from the one in `with-my-output-to-file's definition. <dadinn>how does it guarantee that the with-output-to-file is taken from the context the macro was defined, and not where it was expanded <erkin>The standards leave the underlying implementation to the implementers but most of the time it's an automatically computed gensym system. <erkin>Something like (let ((with-output-to-file~1 (lambda () 'junk))) (with-output-to-file~0 "text.txt" (lambda () (display "foobar")))) <erkin>Where `with-output-to-file~0' is bound to the original top-level definition. <erkin>Again, it's implementation dependent but that's the gist. <dadinn>so the toplevel node I see in the Tree-IL is not a function object itself captured at the point of definition? <dadinn>sorry, my question was in the negative, but actually I meant that that is what I would assume it was :) <erkin>I'm not entirely sure how Guile does it in particular but it captures the environment at the time. <erkin>It's practically impossible to do it by accident though. <erkin>If you do want to break hygiene for sure (eg given a symbol `foo', you want to define `set!-foo' and `get-foo' in a macro), there's `syntax-case', a heavyweight superset of `syntax-rules' that comes with all sorts of utilities for operating on syntax objects. It's admittedly rather baroque and difficult for newbies to grasp (probably to discourage breaking hygiene at all). <erkin>Ah, I need to sleep already. <dadinn>erkin: Good night! thanks a lot! ***apteryx is now known as Guest29175
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<nalkri>Length is a function that if it gets an empty list (the "null?" test) returns 0, if it gets a non-empty list it returns one plus the length of the same list minus its first element <rndd>nalkri: but where sum is stored -_-? <nalkri>In the stack, if it's actually evaluated as a recursive function (I think it would be optimised to a loop really) ***rekado_ is now known as rekado
<rekado>try substituting the calls to “length” <rekado>(length '()) becomes (if (null? '()) 0 (+ 1 (length (cdr '())))) <rekado>that becomes (if #t 0 (+ 1 (length (cdr '())))) <rekado>(if (null? '(a)) 0 (+ 1 (length (cdr '(a))))) <rekado>(null? '(a)) is false, so the “if” expression becomes (+ 1 (length (cdr '(a)))) <chrislck>rndd would find time watching the first few SICP videos very well spent <rndd>ohhh, so it becomes (+1 (+1 (+1 (+1 ... 0) ? <nalkri>Thank you, and sorry for my lack of explanation ***logicmoo is now known as dmiles
<daviid>str1ngs: ar you connected to irc.gim.net (today)? I can't connct to either irc.gnome.org, nor irc.gim.ne today ... <guix-vits>daviid: i'n not str1ngs, but those works for me. <daviid>guix-vits: ok tx, i wonder why not 'here' <daviid>guix-vits: hum, tx that worked ... <daviid>I'll rport that to the gnome tam it's getting mor and more difficult ro connet to their servers ...