Rat.SetString in Go

SetString sets z to the value of s and returns z and a boolean indicating success. s can be given as a (possibly signed) fraction "a/b", or as a floating-point number optionally followed by an exponent. If a fraction is provided, both the dividend and the divisor may be a decimal integer or independently use a prefix of “0b”, “0” or “0o”, or “0x” (or their upper-case variants) to denote a binary, octal, or hexadecimal integer, respectively. The divisor may not be signed. If a floating-point number is provided, it may be in decimal form or use any of the same prefixes as above but for “0” to denote a non-decimal mantissa. A leading “0” is considered a decimal leading 0; it does not indicate octal representation in this case. An optional base-10 “e” or base-2 “p” (or their upper-case variants) exponent may be provided as well, except for hexadecimal floats which only accept an (optional) “p” exponent (because an “e” or “E” cannot be distinguished from a mantissa digit). The entire string, not just a prefix, must be valid for success. If the operation failed, the value of z is undefined but the returned value is nil.