4 ms·

I haven't used the LOOP macro in CL, but the for macro in Clojure is also very powerful and (imho) very readable. My take on the 'versify' example in 4 lines:

by gyim 10y ago

I haven't used the LOOP macro in CL, but the for macro in Clojure is also very powerful and (imho) very readable. My take on the 'versify' example in 4 lines: (for [book book-order chapter (range 1 1000) :when (get-in bible [book (str chapter)]) verse (range 1 1000) :when (get-in bible [book (str chapter) (str verse)])] [book chapter verse (get-in bible [book (str chapter) (str verse)])]) Notice that a single "for" can iterate in a multi-level structure. You can also use :let if you don't want to call (get-in) multiple times (which makes the code shorter, but more redundant and less efficient)

shiro 10y ago
I use CL/Scheme/Clojure at work. I generally prefer comprehension style ('for' in Clojure, srfi-42 in Scheme) but sometimes CL's loop let me save a few nestings. One of such patterns is when I have to accumulate multiple kind of things while I zip through the input. Somewhat contrived example: You have a hashtable that maps integer key to a list of strings. You want to scan it just once and build two lists, strings associated with odd keys and strings associated with even keys. ;; populate input (defvar input (make-hash-table :test 'eql)) (setf (gethash 1 input) '("ichi" "hi")) (setf (gethash 2 input) '("ni" "fu")) (setf (gethash 3 input) '("san" "mi")) (setf (gethash 4 input) '("yon" "shi" "yo")) (setf (gethash 5 input) '("go" "itsu")) ;; loop (loop for k being each hash-key in input when (oddp k) append (gethash k input) into odds when (evenp k) append (gethash k input) into evens finally (return (values odds evens))) ; => ("go" "itsu" "san" "mi" "ichi" "hi") and ("yon" "shi" "yo" "ni" "fu")
- junke 10y ago
  You surely know this but for other people interested: 1. You could add "using (hash-value v)" in the iteration clause to directly have the value (no gethash). 2. There is maphash too.
  - shiro 10y ago
    Right! I tried to construct a terse example in hurry but apparently missed the mark. Usually loop comes handy when conditions and the way to extract values gets more complicated.

by gyim 10y ago

shiro 10y ago

I use CL/Scheme/Clojure at work. I generally prefer comprehension style ('for' in Clojure, srfi-42 in Scheme) but sometimes CL's loop let me save a few nestings. One of such patterns is when I have to accumulate multiple kind of things while I zip through the input. Somewhat contrived example: You have a hashtable that maps integer key to a list of strings. You want to scan it just once and build two lists, strings associated with odd keys and strings associated with even keys. ;; populate input (defvar input (make-hash-table :test 'eql)) (setf (gethash 1 input) '("ichi" "hi")) (setf (gethash 2 input) '("ni" "fu")) (setf (gethash 3 input) '("san" "mi")) (setf (gethash 4 input) '("yon" "shi" "yo")) (setf (gethash 5 input) '("go" "itsu")) ;; loop (loop for k being each hash-key in input when (oddp k) append (gethash k input) into odds when (evenp k) append (gethash k input) into evens finally (return (values odds evens))) ; => ("go" "itsu" "san" "mi" "ichi" "hi") and ("yon" "shi" "yo" "ni" "fu")

junke 10y ago
You surely know this but for other people interested: 1. You could add "using (hash-value v)" in the iteration clause to directly have the value (no gethash). 2. There is maphash too.
- shiro 10y ago
  Right! I tried to construct a terse example in hurry but apparently missed the mark. Usually loop comes handy when conditions and the way to extract values gets more complicated.