Table of Contents
1 lambda-riffs
ALPHA QUALITY – USE AT YOUR OWN RISK
Lambda riffs provides
- a reader macro for building lambdas on the fly
- a few utilities for combining functions
Simply loading the system will introduce the reader macro.
1.1 Examples and Use
To use the system you only need to load it. It adds a adds a single reader macro to your Lisp system.
If this system has any actual users, and if those users are
dissatisfied with the alteration of the global read table, let me know
and I can try adapting this for use with named-readtables.
1.1.1 Normal Use
As normally used, lambda-riffs lets you make quick anonymous
functions. There is a special syntax for making variables that start
with $, for example $x or $my-var.
Here is a basic example
(let ((xs (list 1 2 3 4 5 6))) (remove-if-not (lambda (x) (member x xs)) (loop repeat 20 collect (random 10)))) ;; could be written (let ((xs (list 1 2 3 4 5 6))) (remove-if-not #$(member $x xs) (loop repeat 20 collect (random 10))))
Outputs
(3 1 6 1 4 2 4 6 4 3 5 1 5 3)
The #$ syntax is a reader macro dispatch sequence. Any symbol that
begins with $ inside a form that prepended by #$ will be treated
as a parameter of the anonymous function being defined.
(list (funcall #$(list $x $y) 1 2) ;; two arguments (funcall #$(list $x $x $x) 10)) ;; one argument used in three places
Outputs
((1 2) (10 10 10))
1.1.2 Numbered Parameters
Examples of numbered parameters:
$1,$2$1-with-a-name,$2another-name
If your form uses numbered parameters, then all of the parameters in that form should be numbered.
I.e. numbered parameters begin $ and are followed first by an
integer and then any normal variable name characters.
The effect of numbered parameters is to explicitly specify the order of the parameters in the anonymouse function being defined. Here is ane example:
;; flip the order (funcall #$(list $2-symb $1-symb) 'second 'first)
Outputs
(FIRST SECOND)
In the above 'second is passed in as the first argument, and
'first is passed as the second argument.
Interestingly the numbers do not have to be sequential, they are merely sorted in ascending order:
;; $2 < $4 < $10 (funcall #$(list $10 $2 $4) :two :four :ten)
Outputs
(:TEN :TWO :FOUR)
1.1.3 Nested Forms
You can nest forms by appending an additional $ to the dispatch sequence. Variables of nested forms must include the same number of $ characters as there are in their surrounding dispatch sequence.
This is easer to understand through example:
;; map over a list of lists, subtracting 9 from any member of a list ;; that is greater than 9 ;; without lambda-riffs, you might do: (mapcar (lambda (digit-list) (mapcar (lambda (x) (if (> x 9) (- x 9) x)) digit-list)) '((1 2 3 4 5 6 7 8 9) (10 11 12 12 14 15 16 17 18))) ;; with lambda-riffs, you can do (mapcar #$(mapcar #$$(if (> $$x 9) (- $$x 9) $$x) $digit-list) '((1 2 3 4 5 6 7 8 9) (10 11 12 12 14 15 16 17 18)))
Outputs
((1 2 3 4 5 6 7 8 9) (1 2 3 3 5 6 7 8 9))
1.2 Other tools
1.2.1 rev
(funcall (riff:rev #'cons) 1 2)
(2 . 1)
1.2.2 closure
(let ((x 0)) (let ((inc (riff:closure (incf x)))) (funcall inc :these :will :all :be :ignored) (funcall inc)))
2
1.2.3 mapped
(funcall (riff:mapped #$(+ 10 $x) #$(format nil "--~a--" $x))
100)
(110 "--100--")
1.2.4 lambda-if
(let ((decide (riff:lambda-if #'evenp #$(format nil "It's even: ~a~%" $x) #$(format nil "It's odd: ~a~%" $x)))) (funcall decide 10))
It's even: 10
1.2.5 lambda-cond
(let ((decider (riff:lambda-cond #$(< (length $x) 10) (constantly "It's short.") #$(<= 10 (length $x) 20) #$(format nil "Medium length: ~a" (length $x)) (constantly t) (constantly "Longish")))) (mapcar decider (list "short" "this is a bit longer" "and this one is too long probably")))
("It's short." "Medium length: 20" "Longish")
Created: 2023-02-28 Tue 23:02