{"id":263,"date":"2016-06-17T10:08:28","date_gmt":"2016-06-17T10:08:28","guid":{"rendered":"http:\/\/www.rangakrish.com\/?p=263"},"modified":"2016-06-17T10:10:23","modified_gmt":"2016-06-17T10:10:23","slug":"pattern-matching-with-optima-lisp-library-part-2","status":"publish","type":"post","link":"https:\/\/www.rangakrish.com\/index.php\/2016\/06\/17\/pattern-matching-with-optima-lisp-library-part-2\/","title":{"rendered":"Pattern Matching with Optima Lisp Library – Part 2"},"content":{"rendered":"

Let us continue where we left off last time.<\/p>\n

List Patterns<\/h2>\n

If the incoming argument is a list, then we can use two types of list patterns to match the list elements, namely, list<\/strong> and list*<\/strong>.<\/p>\n

(match ‘(a b c)\u00a0<\/strong><\/em><\/p>\n

((list ‘a ‘b X) X))<\/strong><\/em><\/p>\n

=> c<\/strong><\/em><\/p>\n

This list pattern begins with the list<\/strong> keyword. After that you can specify either the actual elements in the list or variables. If a variable is specified, it will match exactly one element of the list. In this example, we expect two elements \u2018a and \u2018b followed by any element. As expected, the variable X<\/strong> matches the element c<\/strong> in the argument.<\/p>\n

(match ‘(a b)\u00a0<\/strong><\/em><\/p>\n

((list ‘a ‘b X) (print X)))<\/strong><\/em><\/p>\n

=> nil<\/strong><\/em><\/p>\n

Here the pattern looks for a 3 element list, and so it fails.<\/p>\n

You can use the convenient backquote mechanism for list matching:<\/p>\n

(match ‘(a b c)\u00a0<\/strong><\/em><\/p>\n

(`(a b ,x) x))<\/strong><\/em><\/p>\n

=> c<\/strong><\/em><\/p>\n

This saves a few keystrokes and makes it more readable. Note that you have to use the comma before a variable to mark it as a variable.<\/p>\n

The second type of list pattern uses the keyword list*<\/strong>. It allows the use of variables as in the other type, but the last variable will match multiple elements of the incoming list.<\/p>\n

(match ‘(a b c d)\u00a0<\/strong><\/em><\/p>\n

((list* ‘a ‘b X ) X))<\/strong><\/em><\/p>\n

=> (c d)<\/strong><\/em><\/p>\n

You can see that variable X<\/strong> matches the last 2 elements of the argument.<\/p>\n

(match ‘(a b c d)\u00a0<\/strong><\/em><\/p>\n

((list* X ‘b ‘c Y) Y))<\/strong><\/em><\/p>\n

=> (d)<\/strong><\/em><\/p>\n

Here we have 2 variables and Y<\/strong> matches the last (trailing) arguments. Consider this case:<\/p>\n

(match ‘(a b c d)\u00a0<\/strong><\/em><\/p>\n

((list* ‘a ‘b ‘c ‘d X ) t))<\/strong><\/em><\/p>\n

=> t<\/strong><\/em><\/p>\n

Here the variable X will be bound to an empty list. You can replace a variable by an underscore if you don\u2019t need the binding:<\/p>\n

(match ‘(a b c d)\u00a0<\/strong><\/em><\/p>\n

((list* ‘a ‘b ‘c ‘d _ ) t))<\/strong><\/em><\/p>\n

=> t<\/strong><\/em><\/p>\n

Consider the following examples of an empty list as supplied argument:<\/p>\n

(match ‘()\u00a0<\/strong><\/em><\/p>\n

((list* _) t)) ;<\/strong><\/em><\/p>\n

=> t<\/strong><\/em><\/p>\n

(match ‘()\u00a0<\/strong><\/em><\/p>\n

((list* X) t))\u00a0<\/strong><\/em><\/p>\n

=> t<\/strong><\/em><\/p>\n

We can use backquote as we did earlier, with a slight difference:<\/p>\n

(match ‘(a b c d)\u00a0<\/strong><\/em><\/p>\n

(`(a b ,@x) x))<\/strong><\/em><\/p>\n

=> (c d)<\/strong><\/em><\/p>\n

“,@”<\/strong> denotes a list, since this is a multi-value match.<\/p>\n

It is worthwhile to\u00a0 compare list<\/strong> and list*<\/strong> patterns using a common example:<\/p>\n

(match ‘(p q r s)<\/strong><\/em><\/p>\n

\u00a0\u00a0 \u00a0 \u00a0 ((list ‘p ‘q ‘r ‘s) t))\u00a0<\/strong><\/em><\/p>\n

=> t<\/strong><\/em><\/p>\n

(match ‘(p q r s)<\/strong><\/em><\/p>\n

\u00a0\u00a0 \u00a0 \u00a0 ((list* ‘p ‘q ‘r ‘s) t))\u00a0<\/strong><\/em><\/p>\n

=> nil<\/strong><\/em><\/p>\n

(match ‘(p q r s)<\/strong><\/em><\/p>\n

\u00a0\u00a0 \u00a0 \u00a0 ((list* ‘p ‘q ‘r (list ‘s)) t))\u00a0<\/strong><\/em><\/p>\n

=> t<\/strong><\/em><\/p>\n

(match ‘(p q r s)<\/strong><\/em><\/p>\n

\u00a0\u00a0 \u00a0 \u00a0 ((list* ‘p ‘q ‘r x) x))\u00a0<\/strong><\/em><\/p>\n

=> (s)<\/strong><\/em><\/p>\n

Notice how list*<\/strong> has the last element as a list.<\/p>\n

Property Lists<\/h2>\n

If you have a list of key<\/strong> and value<\/strong> pairs, then you can use the plist<\/strong> pattern to match the same.<\/p>\n

(match ‘(:name “Peter” :age 45 :gender “Male” :country “India”)<\/strong><\/em><\/p>\n

\u00a0\u00a0 \u00a0 \u00a0 ((plist :name N :gender G :age A) (list N G A)))<\/strong><\/em><\/p>\n

=> (“Peter” “Male” 45)<\/strong><\/em><\/p>\n

Notice that the order is not important here, and you can match any subset.<\/p>\n

Assoc Lists<\/h2>\n

Optima supports pattern matching in assoc lists, as in list of pairs. See the following examples.<\/p>\n

(match ‘((a . 1) (b . 2) (c . 3))<\/strong><\/em><\/p>\n

\u00a0\u00a0 \u00a0 \u00a0 ((assoc b x) x))\u00a0<\/strong><\/em><\/p>\n

=> 2<\/strong><\/em><\/p>\n

(match ‘((a . 1) (b . 2) (c . 3))<\/strong><\/em><\/p>\n

\u00a0\u00a0 \u00a0 \u00a0 ((and (assoc a x) (assoc b y) (assoc c 3)) (+ x y)))<\/strong><\/em><\/p>\n

=> 3<\/strong><\/em><\/p>\n

(match ‘((a 1) (b 2) (c 3))<\/strong><\/em><\/p>\n

\u00a0\u00a0 \u00a0 \u00a0 ((and (assoc a x) (assoc b y) (assoc c z)) (list x y z)))<\/strong><\/em><\/p>\n

=> ((1) (2) (3))<\/strong><\/em><\/p>\n

(match ‘((a 1) (b 2) (c 3))<\/strong><\/em><\/p>\n

\u00a0\u00a0 \u00a0 \u00a0 ((and (assoc a (list x)) (assoc b (list y)) (assoc c (list z))) (list x y z)))<\/strong><\/em><\/p>\n

=> (1 2 3)<\/strong><\/em><\/p>\n

Hope you can see the difference between using a dotted pair versus a 2-element list.<\/p>\n

We have covered quite a bit\u00a0in this post, and it is time to take a break. In the next post, I will show how\u00a0to apply these ideas in Opusmodus.<\/p>\n","protected":false},"excerpt":{"rendered":"

Let us continue where we left off last time. List Patterns If the incoming argument is a list, then we can use two types of list patterns to match the list elements, namely, list and list*. (match ‘(a b c)\u00a0 ((list ‘a ‘b X) X)) => c This list pattern begins with the list keyword. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[18,17],"tags":[61,62],"class_list":["post-263","post","type-post","status-publish","format-standard","hentry","category-lisp","category-programming","tag-optima","tag-pattern-matching"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p9OLnF-4f","jetpack-related-posts":[{"id":256,"url":"https:\/\/www.rangakrish.com\/index.php\/2016\/06\/09\/pattern-matching-with-optima-lisp-library\/","url_meta":{"origin":263,"position":0},"title":"Pattern Matching with Optima Lisp Library","author":"admin","date":"June 9, 2016","format":false,"excerpt":"In the previous two posts, we looked at external tools and libraries that can be used along with Opusmodus for algorithmic composition. 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This contributes to writing cleaner code, in my opinion. \u00a0 Another environment that I am familiar with, namely Mathematica, boasts of (arguably) the most\u2026","rel":"","context":"In "Elixir"","block_context":{"text":"Elixir","link":"https:\/\/www.rangakrish.com\/index.php\/category\/elixir\/"},"img":{"alt_text":"Symbolic Expressions","src":"https:\/\/i0.wp.com\/www.rangakrish.com\/wp-content\/uploads\/2020\/08\/pattern-mm.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.rangakrish.com\/wp-content\/uploads\/2020\/08\/pattern-mm.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.rangakrish.com\/wp-content\/uploads\/2020\/08\/pattern-mm.png?resize=525%2C300&ssl=1 1.5x"},"classes":[]},{"id":2620,"url":"https:\/\/www.rangakrish.com\/index.php\/2021\/11\/28\/understanding-the-unify-function-in-newlisp\/","url_meta":{"origin":263,"position":3},"title":"Understanding the “unify” Function in “newLisp”","author":"admin","date":"November 28, 2021","format":false,"excerpt":"Unification between two symbolic expressions involves finding substitutions for variables (if any) in the expressions such that the expressions match\u00a0after applying the substitutions. 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