Add '31.nix'

31.nix

@@ -0,0 +1,15 @@
+with import <nixpkgs> { };
+let
+  attrSet = {c = 3; a = 1; b = 2;};
+  #This is an example function that extracts a single value 
+  getSingleVal = (attrSet: x: attrSet.${x});
+
+  #tips: use the map function and access the attribute values 
+  #in the same way as 'getSingleVal'
+  attrVals = l: s: map (field: s.${field}) l;
+
+in
+rec {
+  example = getSingleVal attrSet "a"; #is [1]
+  solution = attrVals ["a" "b" "c"] attrSet; #should be [1 2 3]
+}