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number-parser.ts
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number-parser.ts
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enum NumberParserState {
INITIAL,
UNARY_MINUS,
WHOLE,
DOT,
FRACTION,
EXP_CONST,
EXP_MINUS,
EXP,
UNDERSCORE,
}
export default function numberParser() {
let expr = '';
const invalid = (symbol: string) => {
throw new Error(`Unexpected symbol in "${expr}[${symbol}]"`);
};
const gen = (function* generator(): Generator<number | string, void, string> {
let input = '';
let state: NumberParserState = NumberParserState.INITIAL;
while (true) {
for (const symbol of input) {
switch (symbol) {
case '-':
if (state !== NumberParserState.INITIAL && state !== NumberParserState.EXP_CONST) {
invalid(symbol);
}
if (state === NumberParserState.INITIAL) {
state = NumberParserState.UNARY_MINUS;
} else if (state === NumberParserState.EXP_CONST) {
state = NumberParserState.EXP_MINUS;
}
break;
case '.':
if (state !== NumberParserState.WHOLE) {
invalid(symbol);
}
state = NumberParserState.DOT;
break;
case 'e':
if (state !== NumberParserState.WHOLE
&& state !== NumberParserState.DOT
&& state !== NumberParserState.FRACTION
) {
invalid(symbol);
}
state = NumberParserState.EXP_CONST;
break;
case '_':
if (
state !== NumberParserState.WHOLE
&& state !== NumberParserState.FRACTION
) {
invalid(symbol);
}
state = NumberParserState.UNDERSCORE;
break;
default:
if (!/\d/.test(symbol)) {
invalid(symbol);
}
if (state === NumberParserState.DOT || state === NumberParserState.FRACTION) {
state = NumberParserState.FRACTION;
} else if (
state === NumberParserState.EXP_CONST
|| state === NumberParserState.EXP
|| state === NumberParserState.EXP_MINUS
) {
state = NumberParserState.EXP;
} else {
state = NumberParserState.WHOLE;
}
break;
}
expr += symbol;
}
input = yield expr;
}
}());
gen.next();
Object.defineProperty(gen, 'return', {
value() {
return { value: parseFloat(expr.replace(/_/g, '')), done: true };
},
});
return gen;
}