start, end - bounding index designators of string. The defaults for start and end are 0 and nil, respectively.

radix - a radix. The default is 10.

junk-allowed - a generalized boolean. The default is false.

integer - an integer or false.

pos - a bounding index of string.

parse-integer expects an optional sign (+ or -) followed by a a non-empty sequence of digits to be interpreted in the specified radix. Optional leading and trailing whitespace₁ is ignored.

parse-integer does not recognize the syntactic radix-specifier prefixes #O, #B, #X, and #nR, nor does it recognize a trailing decimal point.

If junk-allowed is false, an error of type parse-error is signaled if substring does not consist entirely of the representation of a signed integer, possibly surrounded on either side by whitespace₁ characters.

The first value returned is either the integer that was parsed, or else nil if no syntactically correct integer was seen but junk-allowed was true.

The second value is either the index into the string of the delimiter that terminated the parse, or the upper bounding index of the substring if the parse terminated at the end of the substring (as is always the case if junk-allowed is false).

 (parse-integer "123")  123, 3
 (parse-integer "123" :start 1 :radix 5)  13, 3
 (parse-integer "no-integer" :junk-allowed t)   NIL, 0