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

["Dr. Arne Babenhauserheide" <arne_bab@web.de>]

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"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

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