Is there a function in Common Lisp that takes a string as an argument and returns a keyword?
Example: (keyword "foo") -> :foo
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alexandria has a make-keyword functionKungi– Kungi2023-08-14 09:59:26 +00:00Commented Aug 14, 2023 at 9:59
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6 Answers
The answers given while being roughly correct do not produce a correct solution to the question's example.
Consider:
CL-USER(4): (intern "foo" :keyword)
:|foo|
NIL
CL-USER(5): (eq * :foo)
NIL
Usually you want to apply STRING-UPCASE to the string before interning it, thus:
(defun make-keyword (name) (values (intern (string-upcase name) "KEYWORD")))
1 Comment
Joshua Taylor
It could be, of course, that OP just had print-case set to
:downcase…Here's a make-keyword function which packages up keyword creation process (interning of a name into the KEYWORD package). :-)
(defun make-keyword (name) (values (intern name "KEYWORD")))
3 Comments
Vatine
Almost, but not quite. When you create a keyword, you must also ensure that you set its value binding to itself.
C. K. Young
@Vatine I only have SBCL to test, and in SBCL,
(symbol-value (intern "FOO" "KEYWORD")) already has the correct value. Besides, Alexandria implements it using the same approach also.Joshua Taylor
@Vatine 11.1.2.3.1 Interning a Symbol in the KEYWORD Package says (emphasis added), "The KEYWORD package is treated differently than other packages in that special actions are taken when a symbol is interned in it. In particular, when a symbol is interned in the KEYWORD package, it is automatically made to be an external symbol and is automatically made to be a constant variable with itself as a value."
There is a make-keyword function in the Alexandria library, although it does preserve case so to get exactly what you want you'll have to upcase the string first.
1 Comment
Joshua Taylor
Or set
print-case to :downcase. intern doesn't do any case modification, so the solution here probably shouldn't either. (Although the example in the question does say (keyword "foo") => :foo, it's probably better to have (... "foo") => :|foo| or (... "FOO") => :FOO.)In case, you can change the string to start with colon sign :
use read-from-string directly.
Here is another version of make-keyword:
(defun make-keyword (name)
(read-from-string (concatenate 'string ":" name)))
1 Comment
Keldon Alleyne
Can't you just do
(read-from-string (concatenate 'string ":" name))?In this example it also deals with strings with spaces (replacing them by dots):
(defun make-keyword (name) (values (intern (substitute #\. #\space (string-upcase name)) :keyword)))
1 Comment
Joshua Taylor
Is there a reason that you'd want to replace spaces with dots? If you intern
"foo bar" you get a symbol with the name "foo bar", and there's no problem with that. intern doesn't replace spaces with dots, either.(intern "foo" "KEYWORD") -> :foo
See the Strings section of the Common Lisp Cookbook for other string/symbol conversions and a detailed discussion of symbols and packages.
3 Comments
C. K. Young
The name needs to be interned in the "KEYWORD" package to be a keyword. e.g., (intern "FOO" "KEYWORD")
nathan
ah yes. The (intern "foo" "KEYWORD") works quite nicely. Thank you.
C. K. Young
In my answer, I've packaged it up into a neat little function, which you may enjoy. :-)