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specs are not types. Your Clojure compiler will have a hard time statically checking specs at compile time.

• iLemming 2y ago
  Yes, Clojure.specs are technically not types, they cannot enforce constraints broadly at compile-time. Yet they still can enforce finer-grained constraints at runtime. From the practical point of view, specs are really great tool for building robust software and have other properties like simplifying property-based testing through automatic generation of test cases. Take for example a trivial example when we need to validate user data with the following constraints: - Age: Must be between 18 and 120. - Name: Must be a non-empty string. - Email: Must follow a valid email format. - Credit Card Number: Must pass the Luhn algorithm check. Something like that is pretty straightforward to achieve in Clojure.spec within 20 lines of code. It's close to impossible to get with any advanced static type system, because type systems can't deal well with custom constraints; they often can't offer detailed, human-readable error messages for the cases like that; they often can't describe complex and nested data structures, or trying to do so would be cumbersome and less expressive. So, they are not types. Okay. Cisco built their cybersecurity platform using Clojure. The market capitalization is about $180B. I imagine this would be a few dozen billions more if they had chosen to use an "actual type system", amiright? ---- edit: After thinking about it a bit more, I have to admit that I spoke too harshly. It's not "close to impossible" You probably can create a type that checks for these constraints, but you would likely need to use a dependent type system or refined types, perhaps something like LiquidHaskell., and it still would be very tricky, especially with the credit card part. In Clojure.spec - it's very trivial.
  • lispm 2y ago
    There is nothing which would require me to use Clojure to check those things. For example... one can easily express all that in Common Lisp: https://www.lispworks.com/documentation/HyperSpec/Body/04_b.htm https://www.lispworks.com/documentation/HyperSpec/Body/04_b.... CL-USER 9 > (defun non-empty-string-p (string) (and (stringp string) (plusp (length string)))) NON-EMPTY-STRING-P CL-USER 10 > (deftype name-type () `(and string (satisfies non-empty-string-p))) NAME-TYPE CL-USER 11 > (deftype age-type () `(integer 18 120)) AGE-TYPE CL-USER 12 > (defun foo (age name) (declare (type age-type age) (type name-type name)) (print (list age name))) FOO also, avoiding SATISFIES: CL-USER 4 > (deftype name-type () `(and string (not (string 0)))) NAME-TYPE CL-USER 5 > (typep "hello" 'name-type) T CL-USER 6 > (typep "" 'name-type) NIL It then has assertions integrated with the condition system, which makes this easily checkable at runtime. SBCL has this extended with type declarations as assertions: http://sbcl.org/manual/index.html#Handling-of-Types http://sbcl.org/manual/index.html#Handling-of-Types Eiffel had promoted Design by Contract for a long time. > Cisco built their cybersecurity platform using Clojure. Cisco uses a lot of software. Your Clojure marketing attempts are getting silly.