There’s a lot of implicit knowledge among Guile developers. Here I gather some useful snippets I found along the way.
log-expression: print variable name and value
During debugging I often want to display variables by name and value. I used to print name and value by hand, but this quickly becomes tedious:
(define foo 'bar) (format #t "foo: ~a\n" foo) ;; or (display 'foo)(display foo)(newline)
Therefore I build me something simpler:
(define-syntax-rule (log-exprs exp ...) (begin (format #t "~a: ~S\n" (quote exp) exp) ...))
Now I can simply log variables like this:
(define foo 'bar) (log-exprs foo) ;; => foo: bar (define bar 'baz) (log-exprs foo bar (list "hello")) ;; foo: bar ;; bar: baz ;; (list hello): ("hello")
Use Guile-yaml to search for the first match in a yaml file
This uses guile-libyaml to parse the yaml file and
(ice-9 match) to recursively search within the file.
The example file is demo1.yml from the guile-yaml repo:
--- doe: "a deer, a female deer" ray: "a drop of golden sun" pi: 3.14159 xmas: true french-hens: 3 calling-birds: - huey - dewey - louie - fred xmas-fifth-day: calling-birds: four french-hens: 3 golden-rings: 5 partridges: count: 1 location: "a pear tree" turtle-doves: two
I’m searching for the first match to "partridges":
(import (yaml) (ice-9 match)) (define demo (read-yaml-file "demo1.yml")) (let match-demo ((demo demo)) (match demo ((("partridges" . b) c ...) b) (else (if (pair? demo) (or (match-demo (cdr demo)) (match-demo (car demo))) #f)))) ;; => (("count" . "1") ("location" . "a pear tree"))
To use this snippet, start guile as
guile -L . in the guile-libyaml repo.
Count occurences of each key in an alist
This was asked by fnstudio in the #guile channel on Freenode.
Given a list of pairs (like xy-coordinates), count how often the first element appears.
(define xydata '((1 . 1)(1 . 2)(1 . 3)(2 . 1)(2 . 2))) (define (assoc-increment! key alist) "Increment the value of the key in the alist, set it to 1 if it does not exist." (define res (assoc key alist)) (assoc-set! alist key (or (and=> (and=> res cdr) 1+) 1))) (fold assoc-increment! '() (map car xydata)) ;; => ((2 . 2) (1 . 3))