CODEWITHSUNDEEP
comparecommon-lisp
randy192
randy192

Reputation: 89

How to compare symbols alphabetically in Common Lisp?

I trying to compare a symbol to another alphabetically, but I can't do this. In particular, I've done this.

CL-USER 1 > (string-lessp 'k 'a)
NIL

CL-USER 2 > (string-lessp 'a 'k)
0

Thank you guys

Upvotes: 1

Views: 397

Answers (1)

Joshua Taylor
Joshua Taylor

Reputation: 85853

In Common Lisp, NIL is false, and anything else is true. So in your transcript, 0 is a true value, indicating that A is before K. Rather than simply returning T and NIL, STRING-LESSP returns a mismatch index:

The inequality functions return a mismatch-index that is true if the strings are not equal, or false otherwise. When the mismatch-index is true, it is an integer representing the first character position at which the two substrings differ, as an offset from the beginning of string1.

0 is the index of the first character where the designated strings don't agree.

Upvotes: 10

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