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/to_float.rs

Created January 6, 2013 17:07
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A simple string-to-float function showing how beautiful rust's pattern matching is.
Raw
to_float.rs
enum ParsedFloat {
FloatValue(float),
FloatSyntaxError,
}
enum FloatParserState {
BeforeSign,
BeforeDot,
AfterDot,
Stop,
}
// return the number of parsed characters
fn parseFloat(src: &str, result:& mut ParsedFloat) -> uint {
let mut state = BeforeSign;
let mut value = 0.0;
let mut sign = 1.0;
let mut decimals = 0.1;
let mut count = 0;
for src.each_char | c | {
match (state, c) {
(Stop, _) => { break; },
(BeforeSign, '-') => {
state = BeforeDot;
sign = -1.0;
},
(BeforeSign, '0'..'9') | (BeforeDot, '0'..'9') => {
value = value * 10.0 + (((c as int) - ('0' as int)) as float);
state = BeforeDot;
},
(BeforeSign, ' ') => {},
(BeforeDot, '.') => { state = AfterDot; }
(AfterDot, '0'..'9') => {
value += (((c as int) - ('0' as int)) as float) * decimals;
decimals /= 10.0;
},
(AfterDot, ' ') => { state = Stop; },
(_,_) => {
*result = FloatSyntaxError;
return 0;
},
}
count += 1;
}
value *= sign;
*result = FloatValue(value);
return count;
}
fn toFloat(s: &str) -> float {
let mut result : ParsedFloat = FloatSyntaxError;
parseFloat(s, &mut result);
match result {
FloatValue(v) => return v,
FloatSyntaxError => fail,
}
}
fn main() {
io::println(fmt!("%f", toFloat(~"12345")));
io::println(fmt!("%f", toFloat(~" 12.345 ")));
io::println(fmt!("%f", toFloat(~"-12345")));
io::println(fmt!("%f", toFloat(~"0")));
io::println(fmt!("%f", toFloat(~" -0.0120 ")));
}
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