string->number

(string->number string) (string->number string radix)

Parses string as a number in radix (default 10) and returns it, or #f when the text is not a number. Integers, ratios and decimals with an optional sign and exponent are read, and +inf.0 -inf.0 +nan.0 -nan.0 in any case. string may itself start with an R7RS prefix -- a radix (#x, #b, #o, #d) and an exactness (#e, #i), each at most once, in either order -- which then wins over radix; #e on a decimal answers the exact rational the digits spell, never rounded through a flonum, and #i converts an exact answer to a flonum. A repeated or unrecognized prefix answers #f.