subseq

(subseq sequence start &optional end)

Returns a fresh subsequence of sequence (a string, a list or a vector) covering the half-open range from index start up to but not including end, using 0-based indexing. When end is omitted or nil the subsequence runs to the end of the sequence. The result has the same kind as the input -- a string for a string, a list for a list, a vector of the same element type for a vector.

The range must satisfy 0 <= start <= end <= (length sequence) -- for a vector with a fill pointer, the length is the fill pointer. Anything else, a negative end included, is a type-error reporting SUBSEQ: invalid bounds START, END for KIND of length N (KIND is string, list or vector) on every backend. Its type-error-datum is the first bound outside its range -- start when it lies outside [0, N], else end, outside [start, N] -- and its type-error-expected-type is that range: (subseq "abc" 2 1) answers 1 and (INTEGER 2 3). A bound that is not an integer (a string, a float, a nil start) lies outside its range too, and the report prints it as given: (subseq "abc" "a") reports SUBSEQ: invalid bounds "a", 3 for string of length 3, its datum "a" and its expected type (INTEGER 0 3).