#pattern-matching

Approximately half of adult Americans’ photographs are stored in facial recognition databases that can be accessed by the FBI, without their knowledge or consent, in the hunt for suspected criminals. About 80% of photos in the FBI’s network are non-criminal entries, including pictures from driver’s licenses and passports. The algorithms used to identify matches are inaccurate about 15% of the time, and are more likely to misidentify black people than white people.

The other day Vincent Toups pointed out that that one can do pattern directed macros in CL. I don’t know where I got the idea that it was only possible in Racket. But I'm glad he made my realise my mistake

To illustrate the advantages I'll rewrite let. Henry Baker wrote the following implementation in Metacircular Semantics for Common Lisp Special Forms.

(defmacro hb-let (vs &body forms) `(funcall #'(lambda ,(mapcar #'car vs) ,@forms) ,@(mapcar #'cadr vs)))

However the implementation doesn't work for clauses without an init form, those that bind the symbol to nil. For example, (let (x) x) signals a type-error in the implementation provided by Baker.

I'll start with let* because it is simpler to implement, using trivia as the pattern matcher.

(defmacro pd-let* (bindings &body body) (match bindings (nil `(funcall (lambda () ,@body))) ((list* (list name value) rest) `(pd-let* ,rest (funcall (lambda (,name) ,@body) ,value))) ;; The guard is to prevent matching the form (x 1 3) and bind name to ;; (x 1 3) and rest to nil. ((guard (list* name rest) (symbolp name)) `(pd-let* ,rest (funcall (lambda (,name) ,@body) nil))) (_ (error "Cannot recognize binding clause in pdl-let: ~A" bindings))))

and some test cases

(pd-let* ((x 1)) (is x 1)) #+error(pd-let* ((x 1 3)) (princ x)) ;; Cannot recognize binding clause in pdl-let: ((X 1 3)) ;; [Condition of type SIMPLE-ERROR] (pd-let* (x) (is x nil)) (pd-let* (x (y 2)) (is x nil) (is y 2))

In the case of let, the idea is the same but because the names have to bound in parallel we have to use one lambda, so we'll accumulate the values and generate the lambda in the base case

(defmacro pd-let (bindings &body body) `(%pd-let ,bindings () () ,@body)) (defmacro %pd-let (bindings names values &body body) (match bindings (nil `(funcall (lambda (,@names) ,@body) ,@values)) ((list* (list name value) rest) `(%pd-let ,rest ,(cons name names) ,(cons value values) ,@body)) ((guard (list* name rest) (symbolp name)) `(%pd-let ,rest ,(cons name names) ,(cons nil values) ,@body)) (_ (error "Cannot recognize binding clause in pdl-let: ~A" bindings)))) (pd-let ((x 1)) (pd-let ((x 3) (y x)) (is x 3) (is y 1)))

but these non-literal descriptions of reality (however literally they are interpreted by the individual) exist because they pattern match to something that really does exist. the idea of bloody mary might be a good way for you to compress the idea of dread and chaos in your world. and your ideal of what a dog is like might be a very real and useful way to understand how you relate to the world (i'm not trying to be mean to otherkin, this is just how i've seen many of them who don't identify that way anymore describe the experience). or it's easier to not kill people because god says not to than because it's an evolutionarily good social contract to have.

Fixed Regular Expressions: Is there an AND operator? #dev #it #asnwer

Regular Expressions: Is there an AND operator?

Obviously, you can use |(pipe?), to represent OR, but can you match and as well?

Specifically, I’m wanting to match paragraphs of text that contain ALL of a certain phrase, but in no particular order.

Answer: Regular Expressions: Is there an AND operator?

Why not use awk? with awk regex AND, OR matters is so simple

awk '/WORD1/ && /WORD2/ &&…

How to: How can I use inverse or negative wildcards when pattern matching in a unix/linux shell?

How can I use inverse or negative wildcards when pattern matching in a unix/linux shell?

Say I want to copy the contents of a directory excluding files and folders whose names contain the word ‘Music’.

cp [exclude-matches] *Music* /target_directory

What should go in place of [exclude-matches] to accomplish this?

Answer: How can I use inverse or negative wildcards when pattern matching in a…

How to: Regular Expressions: Is there an AND operator?

Regular Expressions: Is there an AND operator?

Obviously, you can use |(pipe?), to represent OR, but can you match and as well?

Specifically, I’m wanting to match paragraphs of text that contain ALL of a certain phrase, but in no particular order.

Answer: Regular Expressions: Is there an AND operator?

The order is always implied in the structure of the regular expression. To accomplish what you…