read-from-string

read-from-string is a built-in function in `C source code'.

(read-from-string STRING &optional START END)

Read one Lisp expression which is represented as text by STRING.
Returns a cons: (OBJECT-READ . FINAL-STRING-INDEX).
FINAL-STRING-INDEX is an integer giving the position of the next
remaining character in STRING. START and END optionally delimit
a substring of STRING from which to read; they default to 0 and
(length STRING) respectively. Negative values are counted from
the end of STRING.