Re: define-typed: checking values on proc entry and exit

[Linas Vepstas]

One of my old interests has been storing data as s-expressions. But just
"storing" data is kind of useless, unless you can also search through it,
query it. And, from experience, search/query is mostly useless without
typing. Is `(foo (bar baz))` of type `(surname (given-name occupation))`
or is it `(state (county station))` ? How might one know? I'm not asking
for help here (I have de facto answers to these questions) I'm just ..
offering something to think about.

-- Linas

On Tue, May 14, 2024 at 7:10 PM Dr. Arne Babenhauserheide <arne_bab@web.de>
wrote:

> "Dr. Arne Babenhauserheide" <arne_bab@web.de> writes:
>
> > Zelphir Kaltstahl <zelphirkaltstahl@posteo.de> writes:
> >>
> https://codeberg.org/ZelphirKaltstahl/guile-examples/src/commit/0e231c289596cb4c445efb30168105914a8539a5/macros/contracts
>
> > And the *-versions are ominous: optional and keyword arguments may be
> > the next frontier.
> >
> > I’m not sure how to keep those simple.
>
> I now have a solution:
> https://www.draketo.de/software/guile-snippets#define-typed
>
> ┌────
> │ (import (srfi :11 let-values))
> │ (define-syntax-rule (define-typed (procname args ...) (ret? types ...)
> body ...)
> │   (begin
> │     (define* (procname args ...)
> │       ;; create a sub-procedure to run after typecheck
> │       (define (helper)
> │         body ...)
> │       ;; use a typecheck prefix for the arguments
> │       (map (λ (type? argument)
> │              (let ((is-keyword? (and (keyword? type?)
> │                                      (keyword? argument))))
> │                (when (and is-keyword? (not (equal? type? argument)))
> │                  (error "Keywords in arguments and types are not equal
> ~a ~a"
> │                    type? argument))
> │                (unless (or is-keyword? (type? argument))
> │                  (error "type error ~a ~a" type? argument))))
> │            (list types ...) (list args ...))
> │       ;; get the result
> │       (let-values ((res (helper)))
> │         ;; typecheck the result
> │         (unless (apply ret? res)
> │           (error "type error: return value ~a does not match ~a"
> │                  res ret?))
> │         ;; return the result
> │         (apply values res)))
> │     (unless (equal? (length (quote (args ...))) (length (quote (types
> ...))))
> │       (error "argument error: argument list ~a and type list ~a have
> different size"
> │         (quote (args ...)) (quote (types ...))))
> │     ;; add procedure properties via an inner procedure
> │     (let ((helper (lambda* (args ...) body ...)))
> │       (set-procedure-properties! procname (procedure-properties helper))
> │       ;; preserve the name
> │       (set-procedure-property! procname 'name 'procname))))
> └────
>
> This supports most features of regular define like docstrings, procedure
> properties, multiple values (thanks to Vivien!), keyword-arguments
> (thanks to Zelphir Kaltstahl’s [contracts]), and so forth.
>
> Basic usage:
>
> ┌────
> │ (define-typed (hello typed-world) (string? string?)
> │   typed-world)
> │ (hello "typed")
> │ ;; => "typed"
> │ (hello 1337)
> │ ;; => type error ~a ~a #<procedure string? (_)> 1337
> │ (define-typed (hello typed-world) (string? string?)
> │   "typed" ;; docstring
> │   #((props)) ;; more properties
> │   1337) ;; wrong return type
> │ (procedure-documentation hello)
> │ ;; => "typed"
> │ (procedure-properties hello)
> │ ;; => ((name . hello) (documentation . "typed") (props))
> │ (hello "typed")
> │ ;; type error: return value ~a does not match ~a (1337) #<procedure
> string? (_)>
> └────
>
> Multiple Values and optional and required keyword arguments:
>
> ┌────
> │ (define-typed (multiple-values num) ((λ(a b) (> a b)) number?)
> │   (values (* 2 (abs num)) num))
> │ (multiple-values -3)
> │ ;; => 6
> │ ;; => -3
> │ (define-typed (hello #:key typed-world) (string? #:key string?) "typed"
> #((props)) typed-world)
> │ (hello #:typed-world "foo")
> │ ;; => "foo"
> │ ;; unused keyword arguments are always boolean #f as input
> │ (hello)
> │ ;; => type error ~a ~a #<procedure string? (_)> #f
> │ ;; typing optional keyword arguments
> │ (define (optional-string? x) (or (not x) (string? x)))
> │ (define-typed (hello #:key typed-world) (string? #:key optional-string?)
> │   (or typed-world "world"))
> │ (hello)
> │ ;; => "world"
> │ (hello #:typed-world "typed")
> │ ;; => "typed"
> │ (hello #:typed-world #t)
> │ ;; => type error ~a ~a #<procedure optional-string? (x)> #t
> │ ;; optional arguments
> │ (define-typed (hello #:optional typed-world) (string? #:optional
> optional-string?)
> │   (or typed-world "world"))
> │ (hello)
> │ ;; => "world"
> │ (hello "typed")
> │ ;; => "typed"
> │ (hello #t)
> │ ;; => type error ~a ~a #<procedure optional-string? (x)> #t
> └────
>
> Best wishes,
> Arne
>


-- 
Patrick: Are they laughing at us?
Sponge Bob: No, Patrick, they are laughing next to us.