Elisp: String Compare (Less than)

Less Than

There are many elisp functions for comparisons. The "less than" sign < is a mathematical sign to compare inequality. Elisp has the function < to compare Number or Marker.

(< 1 2)
t
(< 2 1)
nil

It is obvious enough that no explanation is needed.

String Less Than

Elisp also has a "less than" function for Strings, called string-lessp.

(string-lessp "abc" "def")
t
(string-lessp "abc" "ab")
nil

It is a predicate function, meaning that it returns t if the first string, "abc" in the first example, is less than the second strings "def", or nil otherwise.

Elisp have a convention, as noted in elisp info, to end a predicate function with letter "p". Thus, following this convention, string-lessp ends with "p".

Elisp does have string< as an alias for string-lessp. So that you can write the above example:

(string< "abc" "def")
t
(string< "abc" "ab")
nil

"<" vs "p" vs "-p"

It seems like a majority of "less than" functions follow this "lessp" convention, however, there are other functions in Emacs. Here is an incomplete list of "less than" functions I have got from my Emacs with M-x apropos <$\|lessp$\|less-p$.

What functions do you have in your Emacs?

Incomplete List of "less than" functions

• <
• <<
• bibtex-lessp
• byte-string<
• coding-system-lessp
• customize-version-lessp
• elmo-time-less-p
• elmo-time<
• file-attributes-lessp
• gnus-pseudos<
• gnus-string<
• ido-file-extension-lessp
• ido-file-lessp
• mailcap-viewer-lessp
• org-entries-lessp
• org-table-formula-less-p
• org-time<
• recentf-string-lessp
• s-less-p
• skk-string-lessp-in-coding-system
• skk-string<
• string-lessp
• string<
• time-less-p
• version-list-<
• version<

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