3 ms·

Can SBCL actually check at compile time that the arguments to fn-t are bytes? I wonder how that works with Lisp's extreme dynamism. Also wondering about the cal

• reikonomusha 1y ago
  It can detect simple-ish instances, like calling (fn-t "hello" "world") But a good rule-of-thumb is that these compile-time type errors are more of a courtesy, rather than a guarantee. As soon as you abstract over fn-t with another function, like so: (defun g (x y) (fn-t x y)) and proceed to use g in your code, all the static checking won't happen anymore, because as far as g is concerned, it can take any input argument types. CL-USER> (defun will-it-type-error? () (g "x" "y")) ;; compilation WILL-IT-TYPE-ERROR? successful No compile-time warning is issued. Contrast with Coalton: COALTON-USER> (coalton-toplevel (declare fn-t (U8 -> U8 -> U8)) (define (fn-t x y) (* x y)) (define (g x y) (fn-t x y)) (define (will-it-type-error?) (g "hello" "world"))) error: Type mismatch --> <macroexpansion>:8:7 | 8 | (G "hello" "world"))) | ^^^^^^^ Expected type 'U8' but got 'STRING' [Condition of type COALTON-IMPL/TYPECHECKER/BASE:TC-ERROR]