4 ms·

For what it's worth, on a fairly recent SBCL, here's what the compiler/interpreter prints when you enter the author's function: ~> sbcl This is SBCL 1.4.7,

For what it's worth, on a fairly recent SBCL, here's what the compiler/interpreter prints when you enter the author's function: ~> sbcl This is SBCL 1.4.7, an implementation of ANSI Common Lisp. More information about SBCL is available at <http://www.sbcl.org/>. SBCL is free software, provided as is, with absolutely no warranty. It is mostly in the public domain; some portions are provided under BSD-style licenses. See the CREDITS and COPYING files in the distribution for more information. * (defun add-text-padding (str &key padding newline) "Add padding to text STR. Every line except for the first one, will be prefixed with PADDING spaces. If NEWLINE is non-NIL, newline character will be prepended to the text making it start on the next line with padding applied to every single line." (let ((str (if newline (concatenate 'string (string #\Newline) str) str))) (with-output-to-string (s) (map 'string (lambda (x) (princ x s) (when (char= x #\Newline) (dotimes (i padding) (princ #\Space s)))) str)))) ; in: DEFUN ADD-TEXT-PADDING ; (MAP 'STRING ; (LAMBDA (X) ; (PRINC X S) ; (WHEN (CHAR= X #\Newline) (DOTIMES (I PADDING) (PRINC #\ S)))) ; STR) ; --> TRULY-THE SB-KERNEL:%MAP ; ==> ; (MAP-INTO (MAKE-SEQUENCE SB-C::RESULT-TYPE (MIN (LENGTH #:G51))) SB-C::FUN ; #:G51) ; ; caught WARNING: ; The function (LAMBDA (X) :IN ADD-TEXT-PADDING) called by MAP-INTO returns NULL but CHARACTER is expected ; See also: ; The SBCL Manual, Node "Handling of Types" ; ; compilation unit finished ; caught 1 WARNING condition ADD-TEXT-PADDING * Thus, it identifies the exact problem the author describes at the end.

deleted 8y ago
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fiddlerwoaroof 8y ago
Yeah, just because the language doesn’t force you to specify types, doesn’t mean that the compiler can’t infer them for you. What was most eye-opening for me about CL was just how helpful the compiler of a dynamically typed programming language can be.
- fjsolwmv 8y ago
  Checking dynamic types us not the work of a compiler. Checking types at compile time is static type checking. If a type is wholly dynamic (determined at runtime via something like casting to a type specified in user input), the compiler can't check it. (Also, type inference is orthogonal to static vs dynamic typing.)
  - phoe-krk 8y ago
    > Checking dynamic types us not the work of a compiler. Checking types at compile time is static type checking. By your logic, Common Lisp is both dynamically and statically typed, because compile-time type checks are done by the compiler and warnings/errors are signaled whenever proper. More, if you declare (OPTIMIZE SPEED), the compiler is going to print a list of all places where it was unable to infer types on its own and where it expects help from the programmer in form of type declarations for individual variables.
kazinator 8y ago
Also: why would padding be an optional keyword parameter (defaulting to nil!) when it's required to be a non-negative integer for the function to work correctly? Since it is required, it wants to be a required parameter.

deleted 8y ago

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fiddlerwoaroof 8y ago

Yeah, just because the language doesn’t force you to specify types, doesn’t mean that the compiler can’t infer them for you. What was most eye-opening for me about CL was just how helpful the compiler of a dynamically typed programming language can be.

fjsolwmv 8y ago
Checking dynamic types us not the work of a compiler. Checking types at compile time is static type checking. If a type is wholly dynamic (determined at runtime via something like casting to a type specified in user input), the compiler can't check it. (Also, type inference is orthogonal to static vs dynamic typing.)
- phoe-krk 8y ago
  > Checking dynamic types us not the work of a compiler. Checking types at compile time is static type checking. By your logic, Common Lisp is both dynamically and statically typed, because compile-time type checks are done by the compiler and warnings/errors are signaled whenever proper. More, if you declare (OPTIMIZE SPEED), the compiler is going to print a list of all places where it was unable to infer types on its own and where it expects help from the programmer in form of type declarations for individual variables.

kazinator 8y ago

Also: why would padding be an optional keyword parameter (defaulting to nil!) when it's required to be a non-negative integer for the function to work correctly? Since it is required, it wants to be a required parameter.