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Idiomatic scheme and general programming, why only by numbers?

In the schema, routines like +, -, *, / work with different types of numbers, but we don't see any other common routines.

For example, length only works in a list, so vector length and string length are needed.

My guess is that this is because the language does not really offer any mechanism for defining a general procedure (other than cond, of course), such as "class classes" in Haskell, or a standardized object system.

Is there an idiomatic outline of a way to handle common procedures that I am not aware of?

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Finally, I found a very neat solution in the PLT schema:



(require (rename-in scheme [length list-length]))

(define length
 (λ (x)
  ((cond [(list? x) list-length]
         [(string? x) string-length]
         [(vector? x) vector-length]
         [else (error "whatever")]) x)))

(length '(a b c))
(length "abc")
(length #(1 2 3))
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Bearing in mind that all "different types of numbers" - all circuit numbers (ie (number? n)

equal #t

) - this behavior does make sense. +

, -

, *

, /

, And all other arithmetic operators work only with numbers (although in other languages they are classified as different types of numbers int

, long

, float

,, etc.). This is because you cannot explicitly declare number types in the schema.

If you really need a one-size-fits-all solution besides using external libraries, the easiest way is to make your own:



(define org-length length)
(define (length x)
  (cond
    ((string? x) (string-length x))
    ((vector? x) (vector-length x))
    ; keep going ...
    (else (org-length x))))
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No, but you can create your own. Welcome to the Scheme!

I've used Swindle in the past to provide general functionality. It is associated with the PLT scheme . It worked for me, but several years have passed. There may be other alternatives.

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Read the SICP sections 2.4 and 2.5, which cover the implementation of procedures that can work with generic data types by attaching "tags" to data objects. It's also in Lecture 4-B of this MIT video series.

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You really want to have an object system for this. You might want to take a look at Tiny CLOS , which is the de facto standard object system for Chicken Scheme (see the reference manual ), but seems to be available for most Scheme implementations.

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