parserc-java是用java实现的解析器组合子（Parser Combinator）库，可以方便地以自底向上的方式构建复杂的解析器。
/**
* 表达式计算器
*/
class ExprCalc {
private static final Parser<?> digit = range('0', '9');
private static final Parser<Character> add = ch('+').trim();
private static final Parser<Character> sub = ch('-').trim();
private static final Parser<Character> mul = ch('*').trim();
private static final Parser<Character> div = ch('/').trim();
private static final Parser<Character> lp = ch('(').trim();
private static final Parser<Character> rp = ch(')').trim();
private static final Parser<String> digits = digit.many1().map(ExprCalc::join);
private static final Parser<Double> integer = digits.map(Double::parseDouble);
private static final Parser<Double> decimal = seq(digits, ch('.'), digits).map(ExprCalc::join).map(Double::parseDouble);
private static final Parser<Double> number = decimal.or(integer).trim();
private static final Parser<Double> bracketExpr = skip(lp).and(lazy(() -> ExprCalc.expr)).skip(rp);
private static final Parser<Double> negFact = skip(sub).and(lazy(() -> ExprCalc.fact)).map(e -> -e);
private static final Parser<Double> fact = oneOf(number, bracketExpr, negFact);
private static final Parser<Double> term = fact.and(mul.or(div).and(fact).many()).map(ExprCalc::calc);
private static final Parser<Double> expr = term.and(add.or(sub).and(term).many()).map(ExprCalc::calc);
private static final Parser<Double> parser = expr.end();
private static String join(List<?> list) {
return list.stream().map(Objects::toString).collect(Collectors.joining());
}
private static Double calc(Pair<Double, List<Pair<Character, Double>>> p) {
double res = p.getFirst();
for (Pair<Character, Double> pp : p.getSecond()) {
switch (pp.getFirst()) {
case '+':
res += pp.getSecond();
break;
case '-':
res -= pp.getSecond();
break;
case '*':
res *= pp.getSecond();
break;
case '/':
res /= pp.getSecond();
break;
}
}
return res;
}
public static Double eval(String input) {
return parser.parse(input);
}
}/**
* json解析器
*/
class JsonParser {
private static final Parser<String> digit = range('0', '9').map(Objects::toString);
private static final Parser<String> digits = digit.many1().map(JsonParser::join);
private static final Parser<Integer> integer = digits.map(Integer::parseInt).trim();
private static final Parser<Double> decimal = seq(digits, ch('.'), digits).map(JsonParser::join).map(Double::parseDouble);
private static final Parser<String> string = skip(ch('"')).and(not('"').many()).skip(ch('"')).map(JsonParser::join);
private static final Parser<Boolean> bool = strs("true", "false").map(Boolean::parseBoolean).trim();
private static final Parser<Character> objStart = ch('{').trim();
private static final Parser<Character> objEnd = ch('}').trim();
private static final Parser<Character> arrStart = ch('[').trim();
private static final Parser<Character> arrEnd = ch(']').trim();
private static final Parser<Character> colon = ch(':').trim();
private static final Parser<Character> comma = ch(',').trim();
private static final Parser<Object> lazyJsonObj = lazy(() -> JsonParser.jsonObj);
private static final Parser<List<Object>> jsonObjList = lazyJsonObj.and(skip(comma).and(lazyJsonObj).many())
.map(r -> reduceList(r.getFirst(), r.getSecond()));
private static final Parser<List<Object>> arr = skip(arrStart).and(jsonObjList.opt(Collections.emptyList())).skip(arrEnd);
private static final Parser<Pair<String, Object>> pair = string.skip(colon).and(lazyJsonObj);
private static final Parser<List<Pair<String, Object>>> pairList = pair.and(skip(comma).and(pair).many())
.map(r -> reduceList(r.getFirst(), r.getSecond()));
private static final Parser<Map<String, Object>> obj = skip(objStart).and(pairList.opt(Collections.emptyList())).skip(objEnd)
.map(ps -> ps.stream().collect(Collectors.toMap(Pair::getFirst, Pair::getSecond)));
private static final Parser<Object> jsonObj = oneOf(decimal, integer, string, bool, arr, obj);
private static final Parser<Object> parser = jsonObj.end();
private static String join(List<?> list) {
return list.stream().map(Objects::toString).collect(Collectors.joining(""));
}
private static <T> List<T> reduceList(T first, List<T> remain) {
List<T> list = new ArrayList<>();
list.add(first);
list.addAll(remain);
return list;
}
public static Object parse(String input) {
return parser.parse(input);
}
}