IsAString - Sandbox - s c h e m e w i k i . o r g

Testing if an Object is a String

Problem

You need to test if an object is a string.

Solution

The string? predicate is what you want:

> (string? "foo")
#t
> (string? #\f)
#f
> (string? (list #\f #\o #\o))
#f

Notice that a character is not a string. Also, even though we've said that a string is a list of characters, a list of characters is not a string.

-- GordonWeakliem - 05 Apr 2004 The Python Cookbook discusses how simplay asking isinstance is "UnPythonic" and has a discussion on "duck typing", in that their solution just asks if you can concatenate a string to an unknown object. I'm not sure how to address this. You could literally ask if (string-append an-object "") works w/o throwing an exception, but would anyone do this?

(define (is-string? s)
    (with-handlers ((not-break-exn?
                   (lambda (exn) 
                     #f)))
    (let ((s2 (string-append s ""))) #t)))