foo.chpl

var idToString : [1..0] string;

var ingDom : domain(string);
var ingredients : [ingDom] int;

var f = open("info.txt", iomode.r);

for line in f.lines() {
  const ingredient = line.strip(); // get rid of \n

  if ingDom.member(ingredient) == false {
    idToString.push_back(ingredient);
    const ID = idToString.domain.last;
    assert(idToString[ID] == ingredient);

    ingDom.add(ingredient);
    ingredients[ingredient] = ID;
  }
}

for i in ingDom {
  const ID = ingredients[i];
  writeln(i, " => ", ID);
  assert(idToString[ID] == i);
}

info.txt

carrots
lettuce
potato
fries
candy
lettuce
lettuce
candy
potato
fries
carrots
carrots
salad