Sha256 Hashes in Scheme

Here’s the translation of the SHA256 Hashes example to Scheme:

(import (rnrs)
        (rnrs bytevectors)
        (srfi :13)
        (srfi :39)
        (srfi :69))

;; SHA256 hashes are frequently used to compute short identities for binary
;; or text blobs. For example, TLS/SSL certificates use SHA256
;; to compute a certificate's signature. Here's how to compute
;; SHA256 hashes in Scheme.

;; Scheme doesn't have a built-in SHA256 implementation in its standard library,
;; so we'll use a hypothetical SHA256 library. In practice, you'd need to use
;; a third-party library or implement SHA256 yourself.

(define (sha256 s)
  (let* ((h (make-sha256-context))
         (_ (update-sha256! h (string->utf8 s)))
         (bs (finalize-sha256! h)))
    bs))

(define (main)
  (let* ((s "sha256 this string")
         (bs (sha256 s)))
    (display s)
    (newline)
    (display (bytevector->hex-string bs))
    (newline)))

(main)

In this Scheme translation:

1. We import necessary libraries for working with bytevectors and strings.

2. We define a sha256 function that takes a string, converts it to UTF-8, and returns a bytevector of the hash. This function uses hypothetical make-sha256-context, update-sha256!, and finalize-sha256! functions, which would need to be provided by a SHA256 library.

3. In the main function, we create a string, compute its SHA256 hash, and then display both the original string and the hash (converted to a hexadecimal string representation).

4. Finally, we call the main function to execute our program.

To run this program, you would save it to a file (e.g., sha256-hashes.scm) and run it with a Scheme interpreter that supports the required libraries.

Note that Scheme doesn’t have built-in support for cryptographic functions like SHA256. In a real-world scenario, you would need to use a cryptography library that provides these functions. The exact implementation and usage would depend on the specific library you choose.

Remember, if you need cryptographically secure hashes, you should carefully research hash strength!