guile-examples/web-development/example-markdown-blog/notes.org

Useful code snippets

Convert byte vector query string or form data to an alist

The following code is taken from https://notabug.org/jbranso/autoassign/src/master/decode.scm. Comments have been added and code formatting has been changed. Some code has also been changed, for example some define expressions have been rewritten into a let* expression. Semantically though there should be no changes.

(define-module (decode))

(use-modules ;; for match-lambda (ice-9 match)) (use-modules ;; for utf8->string (rnrs bytevectors)) (use-modules ;; for append-map (srfi srfi-1)) (use-modules ;; for cut (srfi srfi-26)) (use-modules ;; for uri-decode (web uri))

(define (acons-list k v alist) "Add V to K to alist as list" (let ([value (assoc-ref alist k)]) (if value (let ((alist (alist-delete k alist))) (acons k (cons v value) alist)) (acons k (list v) alist))))

(define (list->alist lst) "Build a alist of list based on a list of key and values.

Multiple values can be associated with the same key" (let next ([lst lst] [out '()]) (if (null? lst) out (next (cdr lst) (acons-list (caar lst) (cdar lst) out)))))

(define-public (decode bv) "Convert BV querystring or form data to an alist" (let* ([string (utf8->string bv)] [pairs (map ;; The procedure cut from srfi-26 returns a procedure, which already ;; has some of the arguments specified and still needs to get the ;; arguments in positions of the <>. The following will return a ;; procedure, which splits strings at an equal sign. (cut string-split <> #\=) ;; The procedure append-map from srfi-1 is equivalent to first using ;; map and then using append to make one list out of all the partial ;; lists. ;; semi-colon and amp can be used as pair separator in URLs (append-map (cut string-split <> #\;) (string-split string #\&)))]) (list->alist ;; When query parameters are given in the URI, they need to be decoded, ;; because when they are given, they are, and need to be, URI encoded. (map ;; The procedure match-lambda returns a procedure, which takes one ;; argument and then tries to match the argument with each clause in ;; turn. If one clause matches the argument, its corresponding expression ;; is evaluated. (match-lambda ;; If there is a key value pair ... [(key value) ;; ... uri-decode the key and the value and return those decoded values ;; as a pair. (cons (uri-decode key) (uri-decode value))]) ;; Do this for all key value pairs. pairs))))