Thank you so much Alex, I just love this - #-> (and (= "." (car Lst)) (on P)) :)
The sample you shared certainly looks more elegant. I have a follow up question though - we seem to do 3 iterations in it, the main one, one for length and one for member. Coming to think of it, given my scenario, its negligible. However, in general, is this recommended - granted that it's still linear. I'd love to hear your thoughts on this. About 1 cell per character - if I understand correctly, that would be 16bytes per character on 64 bit ... does that mean that a parser written in PicoLisp would require 16 times more memory compared to C? Regards, Kashyap On Sat, Mar 30, 2019 at 8:33 AM Alexander Burger <a...@software-lab.de> wrote: > Hi Kashyap, > > > While working on the json library I had to write a string to float > > I recommend to use upper case for locally bound symbols > > (de isNum (N) > (or (= "." N) (num? (format N))) ) > > The 'num?' can be omitted, because 'format' returns NIL if it does not > succeed. > > (or (= "." N) (format N)) ) > > > > function. In a list of characters when I encounter a digit, I'd like to > go > > over the rest of the list and consume all the digits (and possibly a > > period) that form a number. I'd appreciate some feedback from a Lispiness > > and PicoLispiness point of view :) > > Just a few notes: > > (de read-num (N Lst) > (let > (C 0 # count of digits found > P F # period found? > > 'F' (or 'f' in the original) is probably wrong here. It is not bound and > contains an unpredictable value. You meant > > P NIL # period found? > > Ds (pack N > (make > (while (isNum (car Lst)) > (ifn P (setq P (= "." (car Lst)))) > #-> (and (= "." (car Lst)) (on P)) > (setq C (inc C)) > #-> (inc 'C) > > (link (pop Lst)) > (setq Lst (cdr Lst)) ) ) ) > #-> (link (++ Lst)) # Same as (link (pop 'Lst)) > > (pop Lst) does not pop the list, but pops from the CAR of that list which > happens to be a transient symbol with its value being itself. So it luckily > worked ;) > > result (if P Ds (pack Ds ".0")) ) # if a period was not present > then add a ".0" > (list C result)) ) > > > There are many ways to write this function. I don't know which would be > the best > one, perhaps I would go with this: > > (de read-num (N Lst) > (let L > (make > (while (isNum (car Lst)) > (link (++ Lst)) ) ) > (list > (length L) > (pack N L (unless (member "." L) ".0")) ) ) ) > > > > > On a related note - Is chopping a reasonable way to break an input file > > into characters while parsing? > > Yes, but you don't need to 'chop' explicitly. You can call (char) to get a > single character, (line) to get a (chopped) list of characters, or (till) > to get > a list of all characters in the file (usually not the best solution). > > You may look at e.g. @lib/xm.l to see a non-trivial (yet still simple) > parser. > > > > I mean, would each character now occupy one > > cell? > > Yes. > ☺/ A!ex > > -- > UNSUBSCRIBE: mailto:picolisp@software-lab.de?subject=Unsubscribe >
