private Val atom() {
Token t = lex.nextToken();
if (t.type == Token.Type.number) {
return new Num((Double) t.value);
} else if (t.type == Token.Type.string) {
return new Str("" + t.value);
} else if (t.type == Token.Type.id) {
Val res = env.val(t.value.toString());
if (res.getType() == Val.Type.nil) {
res = new Id("" + t.value);
Val expr = expr();
env.set(t.value.toString(), expr);
}
return res;
} else if (t.matchOperator("(")) {
Val v = expr();
t = lex.nextToken();
if (!t.matchOperator(")")) {
throw new EvalException("lexical error: ) was expected");
}
return v;
} else {
lex.returnToken();
return Nil.NIL;
}
}
private Val moreTerms(Val val) {
Token t = lex.nextToken();
if (t.matchOperator("+")) {
Val rVal = levelFactor();
Val eval;
if (val.getType() == Val.Type.string) {
eval = new Str(val.evalStr(env) + rVal.evalStr(env));
} else {
eval = new Num(val.evalNum(env) + rVal.evalNum(env));
}
return moreTerms(eval);
} else if (t.matchOperator("-")) {
Val rVal = levelFactor();
Val eval = new Num(val.evalNum(env) - rVal.evalNum(env));
return moreTerms(eval);
} else {
lex.returnToken();
return val;
}
}