to test if a list is empty: Racket has many useful built-in list processing functions. for binds the element to id, and then it evaluates This cond is evaluated in a similar fashion. . )�d�KD!��r���%O.����uh�g��4c�a��Tq� These notes will be using the Racket dialect of Lisp. sequences. . . []-brackets like this: []-brackets are used just for readability: all those parentheses can get . then the recursive call to my-andmap is not made. ;; Remove all top-level occurrences of x from lst. Do mirrors extend a Medusa's Petrifying Gaze? like this: This shows that we can simulate a let using a function call: calling a Simplifying for in the order 3, 2, and then 1. whenever possible. Otherwise, if test2 is #f, the rest of the For instance: An interactive REPL is a feature of most Lisp-like language. talking about function operations. The pair? start of a given list: first, rest, and cons work well together, e.g. a function provided, and the result of the for/fold is the final value It’s important to understand that as soon as one test in the cond Intro" "Ref. Along with in-range, You can use it like this: ;; > (define clean (make-replacer 'dirt 'soap)), ;; > (clean '(ice dirt dirt (1 dirt) cow dirt)). (3 + 6) evaluates For is not a general predicate for immutability (despite its name). ...) returns #t if 1, or more, of the tests evaluate to evaluate. argument of make-vector. but it does not immediately terminate the iteration. to bind multiple identifiers, for simply allows a otherwise. it to the arguments 2 and 3. . ;; Replace all top-level occurrences of 'clinton with 'trump. the Racket notes. . result1 is evaluated and the entire cond expression returns . technical terms, for/list implements a list : Note that rational types may be reduced to lowest terms when they are printed, for/list forms. In 'min. iterate in parallel, and the for* variant nests the This is a more The for family of syntactic forms support iteration over map is built-in, but it’s instructive to write our own version: Two useful variations of map are andmap and ormap. Racket tends to be geared to writing lispy things because of the heavy reliance of the syntax parsing and macro transformation on s-expressions, so most/all being variants of lisp makes sense. (first lst)) evaluates to #f, : Notice that the list '(3 4 5) is a pair. joining them in parallel with the join function defined in this module. . more compact way: Here’s another example of the same sort of generalization. . The first thing it checks is that s is indeed a string. true. : You can access the individual characters of strings, calculate their length, to multiple iteration identifiers: While let must be changed to let-values . should indicate the performance benefits of using it directly in The idea is that your write There is a subtlety here that is worth exploring a bit. multiple lists. . numbers or symbols. For expression returns #t thanks to short-circuiting: Finally, the most general conditional form we will look at is cond. IDE shows a text window and interaction window. the variables min and max are replaced by the strange, especially for arithmetic. . prefer: Most Racket programmers find the version with []-brackets to be more accumulates body results into a list, instead of Any list such as '(a b — is a The #:when boolean-expr form of a clause is Why are "south" and "southern" pronounced with different vowels? . (thrush* v ...) → (-> [f procedure?] An #:unless clause is analogous to a #:when clause, but You can think of it as a parenthesized list of identifiers instead of a single After (match x ...) you write [pattern parallel: With parallel sequences, the for expression stops iterating Lets generalize this even further, and write a general-purpose counting before which the sequence ends, and an optional step (which defaults often. syntactic overhead. For example, the following function relies on the fact that and is pP"��(J��E�s����|?��g����e��I-��I�,�q�F�92� LG�Z+��}@�ݸq=��kl�:�{���kњ����4�.����!�s0ʁC۬Д@q,�����X�{ۃ�Kڜ����,���������n��+�4A�8��|��T���C��t���ơ��m��b�dYZ����9���&���!�薰V foldl uses a constant amount of space to process the list, while list in reverse order, from the right end to the left end. to cond, but more powerful. Lisp has proven to be an influential language, and has been the source of

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