parse-integer

(parse-integer string &key start end radix junk-allowed)

Parses an integer from a string, skipping surrounding whitespace. :start/:end bound the parsed region, :radix selects the base (default 10) and :junk-allowed, when non-nil, stops at the first non-digit and returns the integer parsed so far (or nil if none). Without :junk-allowed, any trailing non-whitespace character is an error. The second return value is the position where parsing stopped, ready to feed back into :start. The full keyword set and both values work identically on every backend; usable as a first-class value (#'parse-integer).

(parse-integer "42") returns 42, and (parse-integer "x9x" :start 1 :end 2) returns 9 by parsing only the bounded region.