Command Line Flags in Scheme

Here’s the translation of the Go code to Scheme, along with explanations in Markdown format suitable for Hugo:

Command-line flags are a common way to specify options for command-line programs. For example, in `wc -l` the `-l` is a command-line flag.

Scheme doesn't have a built-in library for parsing command-line arguments like Go's `flag` package. However, we can implement a simple parsing mechanism using the `command-line-arguments` procedure, which is available in many Scheme implementations. Here's an example of how we might implement command-line flag parsing in Scheme:

```scheme
(define (parse-args args)
  (let ((flags '())
        (rest '()))
    (let loop ((remaining args))
      (cond
        ((null? remaining) (cons flags rest))
        ((string-prefix? "--" (car remaining))
         (let* ((flag (string-drop (car remaining) 2))
                (key-value (string-split flag #\=)))
           (if (= (length key-value) 2)
               (begin
                 (set! flags (cons (cons (car key-value) (cadr key-value)) flags))
                 (loop (cdr remaining)))
               (error "Invalid flag format" (car remaining)))))
        (else
         (set! rest (append rest (list (car remaining))))
         (loop (cdr remaining)))))))

(define (main)
  (let* ((parsed-args (parse-args (cdr (command-line-arguments))))
         (flags (car parsed-args))
         (rest (cdr parsed-args)))
    
    (define (get-flag key default)
      (cond
        ((assoc key flags) => cdr)
        (else default)))
    
    (let ((word (get-flag "word" "foo"))
          (numb (string->number (get-flag "numb" "42")))
          (fork (string=? (get-flag "fork" "false") "true"))
          (svar (get-flag "svar" "bar")))
      
      (display (string-append "word: " word)) (newline)
      (display (string-append "numb: " (number->string numb))) (newline)
      (display (string-append "fork: " (if fork "true" "false"))) (newline)
      (display (string-append "svar: " svar)) (newline)
      (display "tail: ") (write rest) (newline))))

(main)

This Scheme program implements a basic command-line flag parsing mechanism. Here’s how it works:

We define a parse-args function that takes a list of command-line arguments and separates them into flags (key-value pairs) and remaining arguments.
In the main function, we use parse-args to process the command-line arguments.
We define a get-flag helper function to retrieve flag values with default fallbacks.
We then extract and display the values for our flags (word, numb, fork, and svar), as well as any remaining arguments.

To run this program, save it to a file (e.g., command-line-flags.scm) and execute it using your Scheme interpreter. For example:

$ scheme command-line-flags.scm --word=opt --numb=7 --fork=true --svar=flag extra1 extra2
word: opt
numb: 7
fork: true
svar: flag
tail: (extra1 extra2)

Note that the exact command to run the Scheme program may vary depending on your Scheme implementation.

This implementation doesn’t provide automatic help text generation or type checking for the flags. In a more robust implementation, you might want to add these features, as well as error handling for invalid flag formats or values.

Remember that Scheme, being a minimalist language, doesn’t provide as many built-in features as some other languages. This example demonstrates how you can implement basic command-line argument parsing, but for more complex needs, you might want to use or create a dedicated library.

Command Line Arguments in Scheme

Context in Scheme

Learn X By Example

Title here

Command Line Flags in Scheme