Basic Operations on Datatypes in Nix

with import <nixpkgs> { };
with lib;
let
  attr = {a="a"; b = 1; c = true;};
  s = "b";
in
{
  #replace all X, everything should evaluate to true
  ex0 = isAttrs attr;
  ex1 = attr.a == "a";
  ex2 = attr.${s} == 1;
  ex3 = attrVals ["c" "b"] attr == [ true 1 ];
  ex4 = attrValues attr == [ "a" 1 true ];
  ex5 = builtins.intersectAttrs attr {a="b"; d=234; c="";} 
    == { a = "b"; c = "";};
  ex6 = removeAttrs attr ["b" "c"] == { a="a"; };
  ex7 = ! attr ? a == false;
}

let
  list = [ { name = "foo"; value = 123; }
           { name = "bar"; value = 456; } ];
  string = ''{"x": [1, 2, 3], "y": null}'';
in 
{
  ex0 = builtins.listToAttrs list == { foo = 123; bar = 456; };
  ex1 = builtins.fromJSON string == { x = [ 1 2 3 ]; y = null; };
}

let
  attrSetBonus = {f = {add = (x: y: x + y);
                       mul = (x: y: x * y);};
                  n = {one = 1; two = 2;};};
in
rec {
  #Bonus: use only the attrSetBonus to solve this one
  exBonus = with attrSetBonus; 5 == f.add ( f.mul n.two n.two ) n.one;
}

with import <nixpkgs> { };
with stdenv.lib;
let
  attrSet = { a = -2; b = 3; };
in 
{
  ex0 = lib.mapAttrs (k: v: v * 7) attrSet;
}

with import <nixpkgs> { };
with stdenv.lib;
let
  list = [2 "4" true false {a = 27;} false 3];
  f = x: isString x;
  s = "foobar";
in
{
  #replace all X, everything should evaluate to true
  ex00 = isList list;
  ex01 = elemAt list 2 == true;
  ex02 = length list == 7;
  ex03 = last list == 3;
  ex04 = filter f list == [ "4" ];
  ex05 = head list == 2;
  ex06 = tail list == [ "4" true false {a = 27;} false 3 ];
  ex07 = remove true list == [ 2 "4" false {a = 27;} false 3 ];
  ex08 = toList s == [ "foobar" ];
  ex09 = take 3 list == [ 2 "4" true ];
  ex10 = drop 4 list == [ {a = 27;} false 3 ];
  ex11 = unique list == [ 2 "4" true false {a = 27;} 3 ];
  ex12 = list ++ ["x" "y"] == [ 2 "4" true false {a = 27;} false 3 "x" "y" ];
}

let
  numbers = [1 2 3 4];
in
{
  #multiplies every number by 2
  example = map (n: n * 2) numbers; 
}

with import <nixpkgs> { };
with lib;
let
  list = ["a" "b" "a" "c" "d" "a"];
  intList = [ 1 2 3 ];
  countA = fold (x: y: if (x == "a") then (y+1) else y) 0;
  mulB = fold (x: y: [ (2 * x) ] ++ y) [8];
in
rec {
  example = fold (x: y: x + y) "z" ["a" "b" "c"]; #is "abcz"
  ex0 = countA list; #should be 3
  ex1 = mulB intList; #should be [ 2 4 6 8 ]
}

reverseList = lib.fold (x: y: y ++ [ x ]) [];

with import <nixpkgs> { };
let
  listOfNumbers = [2 4 6 9 27];
  myMap = a: b: lib.fold (x: y: [ (a x) ] ++ y) [] b; 
in
rec {
  #your map should create the same result as the standard map function
  example = map (x: builtins.div x 2) listOfNumbers; 
  result = myMap (x: builtins.div x 2) listOfNumbers;
}