transducers prezzo source

transducers.js

inc_map = function (ary) {
  return ary.reduce(
    function(result, input) {
    return result.concat(input + 1);
  }, []);
};

inc_map([1, 2, 3]);

map = function(transform, ary) {
  return ary.reduce(function(result, input) {
    return result.concat(transform(input));
  }, []);
};

double = function(x) { return x * 2; };

map(double, [1, 2, 3]);

filter = function(predicate, ary) {
  return ary.reduce(function(result, input) {
    if(predicate(input)) {
      return result.concat(input);
    } else {
      return result;
    }
  }, []);
}

is_even = function(x) { return x % 2 === 0; };

filter(is_even, [1, 2, 3, 4]);

map(double, filter(is_even, [1, 2, 3, 4]));

concat = function(a, b) { return a.concat([b]) };

concat([1, 2, 3], 4)

mapper = function(transform) {
  return function(result, input) {
    return concat(result, transform(input));
  };
};

[1, 2, 3, 4].reduce(mapper(double), [])

filterer = function(predicate) {
  return function(result, input) {
    if(predicate(input)) {
      return concat(result, input);
    } else {
      return result;
    }
  };
};

[1, 2, 3, 4].reduce(filterer(is_even), []);

identity = function(x) { return x; };

[1, 2, 3].reduce(mapper(identity), []);

filterer = function(predicate) {
  return function(result, input) {
    if(predicate(input)) {
      return mapper(double)(result, input);
    } else {
      return result;
    }
  };
};

[1, 2, 3, 4].reduce(filterer(is_even), []);

mapping = function(transform) {
  return function(reduce) {
    return function(result, input) {
      return reduce(result, transform(input));
    };
  };
};

filtering = function(predicate) {
  return function(reduce) {
    return function(result, input) {
      if(predicate(input)) {
        return reduce(result, input);
      } else {
        return result;
      }
    };
  };
};

[1, 2, 3, 4].reduce(mapping(double)(concat), []);

filter_and_double = filtering(is_even)(mapping(double)(concat));

[1, 2, 3, 4].reduce(filter_and_double, []);

key_adder = function(result, input) { result[input] = true; return result };
filter_and_double = filtering(is_even)(mapping(double)(key_adder));

[1, 2, 3, 4].reduce(filter_and_double, {});