(define "(if ...)" (= ()
  (should "(if) returns null." (=> ()
    (assert null (if).
  ).
  (should "(if cond) returns null." (=> ()
    (assert null (if null).
    (assert null (if 0).
    (assert null (if 1).
    (assert null (if true).
    (assert null (if false).
  ).
  (should "(if cond x) returns x if condition is evaluated to true." (=> ()
    (assert 10 (if true 10).
    (assert 10 (if (1 === 1) 100 10).

    (assert 10 (if 1 10).
    (assert 10 (if (1 + 1) 100 10).

    (assert 10 (if "" 10).
    (assert 10 (if ("x" + "y") 100 10).
  ).
  (should "(if cond x) returns null if condition is evaluated to false." (=> ()
    (assert null (if null 10).
    (assert null (if null 100 10).

    (assert null (if false 10).
    (assert null (if (1 == 0) 100 10).

    (assert null (if 0 10).
    (assert null (if (1 - 1) 100 10).
  ).
  (should "(if cond x else y) returns y if condition is evaluated to false." (=> ()
    (assert 10 (if null else 10).
    (assert 10 (if null else 100 10).

    (assert 10 (if false 100 else 10).
    (assert 10 (if (1 == 0) 101 11 else 100 10).

    (assert 20 (if 0 (1 + 1) else (10 + 10).
    (assert 20 (if (1 - 1) (1 + 1) else (100 + 100) (10 + 10).
  ).
).

(define "(while ...)" (= ()
  (should "(while) returns null." (=> ()
    (assert null (while).
  ).
  (should "(while cond) returns if condition is evaluated to false." (=> ()
    (assert null (while null).
    (assert null (while xxx).

    (assert null (while 0).
    (assert null (while (1 - 1).

    (assert null (while false).
    (assert null (while (1 == 0).
  ).
  (should "(while cond statements ...) repeatedly evaluates statements until condition is evaluated to false." (=> ()
    (var i 0)
    (assert 10 (while (i < 10) (++ i).

    (let i 0)
    (var count 0)
    (assert 10 (while (i < 10) (count ++) (i += 2).
    (assert 5 count)
  ).
  (should "(continue ) skips all statements after." (=> ()
    (var i 0)
    (assert null (while (i < 10) (++ i) (continue) (i ++).
    (assert 10 i)
  ).
  (should "(continue value) applies value as the result of while loop." (=> ()
    (var i 0)
    (assert 100 (while (i < 10) (++ i) (continue 100) (i ++).
    (assert 10 i)
  ).
  (should "(continue values ...) applies the array of values as the result of while loop." (=> ()
    (var i 0)
    (var result (while (i < 10) (++ i) (continue 10 100) (i ++).
    (assert 10 i)

    (assert (result is-an array).
    (assert 10 (result 0).
    (assert 100 (result 1).
  ).
  (should "(break value) applies value as the result of while loop." (=> ()
    (var i 0)
    (assert 10 (while (i < 10) (++ i) (if (i > 5) (break 10).
    (assert 6 i)
  ).
  (should "(break values ...) applies the array of values as the result of while loop." (=> ()
    (var i 0)
    (var result (while (i < 10) (++ i) (if (i > 5) (break 10 100).
    (assert 6 i)
    (assert (result is-an array).
    (assert 10 (result 0).
    (assert 100 (result 1).
  ).
).

(define "(in ...)" (= ()
  (should "(in) returns (iterator empty)." (=> ()
    (assert (iterator empty) (in).
  ).
  (should "(in null) returns (iterator empty)." (=> ()
    (assert (iterator empty) (in null).
    (assert (iterator empty) (in null null).
    (assert (iterator empty) (in null (1, 10).
  ).
  (should "(in a-range) returns an iterator for the range." (=> ()
    (var iter (in (0, 3).
    (assert (iter is-an iterator).

    (var values (iter collect).
    (assert (values is-an array).
    (assert 3 (values length).
    (assert 0 (values 0).
    (assert 1 (values 1).
    (assert 2 (values 2).
  ).
  (should "(in a-tuple) returns an iterator for the tuple." (=> ()
    (var iter (in (quote 10, true, x).
    (assert (iter is-an iterator).

    (var values (iter collect).
    (assert (values is-an array).
    (assert 3 (values length).
    (assert 10 (values 0).
    (assert true (values 1).
    (assert (`x) (values 2).
  ).
  (should "(in an-array) returns an iterator for the array." (=> ()
    (var iter (in (@ 6, 4, 2).
    (assert (iter is-an iterator).

    (var values (iter collect).
    (assert (values is-an array).
    (assert 3 (values length).
    (assert 6 (values 0).
    (assert 4 (values 1).
    (assert 2 (values 2).
  ).
  (should "(in an-object) returns an iterator for the object." (=> ()
    (var iter (in (@ x: 1, y: 2, z: 3).
    (assert (iter is-an iterator).

    (var keys (@).
    (var values (@).
    (iter for-each (=>(k, v) (keys push k) (values push v).

    (assert (keys is-an array).
    (assert 3 (keys length).
    (assert "x" (keys 0).
    (assert "y" (keys 1).
    (assert "z" (keys 2).

    (assert (values is-an array).
    (assert 3 (values length).
    (assert 1 (values 0).
    (assert 2 (values 1).
    (assert 3 (values 2).
  ).
  (should "(in other-value) returns (iterator empty)." (=> ()
    (assert (iterator empty) (in type).
    (assert (iterator empty) (in bool).
    (assert (iterator empty) (in string).
    (assert (iterator empty) (in number).
    (assert (iterator empty) (in date).
    (assert (iterator empty) (in symbol).
    (assert (iterator empty) (in tuple).
    (assert (iterator empty) (in function).
    (assert (iterator empty) (in lambda).
    (assert (iterator empty) (in operator).
    (assert (iterator empty) (in iterator).
    (assert (iterator empty) (in array).
    (assert (iterator empty) (in object).

    (assert (iterator empty) (in true).
    (assert (iterator empty) (in false).
    (assert (iterator empty) (in 0).
    (assert (iterator empty) (in 1).
    (assert (iterator empty) (in "").
    (assert (iterator empty) (in "1234").
    (assert (iterator empty) (in (date of 1).
    (assert (iterator empty) (in (`x).
    (assert (iterator empty) (in (operator empty).
  ).
).

(define "(for ... ...)" (= ()
  (should "(for) returns null." (=> ()
    (assert null (for).
  ).
  (should "(for value) returns null." (=> ()
    (assert null (for x).
    (assert null (for (x y).
    (assert null (for (x y z).
  ).
  (should "(for an-iterable statements ...) puts current value into default variable: _." (=> ()
    (var a 0)
    (assert 1 (for (1, 2) _).
    (assert 2 (for (quote 2) _).
    (assert 3 (for (@ 3) _).
    (assert "x" (for (@ x: 4) _).
  ).
  (should "(for a-range statements ...) traverses all values in the range and returns final result." (=> ()
    (assert null (for (0, 0) (++ a).
    (assert 1 (for (0, 1) (++ b).
    (assert 10 (for (0, 5) (++ c) (++ c).
  ).
  (should "(for an-array statements ...) traverses all values in the array and returns final result." (=> ()
    (assert null (for (@) (++ a).
    (assert 1 (for (@ 1) (++ b).
    (assert 2 (for (@ 1, 2) (++ c).
    (assert 3 (for (@ 1, 2, 3) (++ d).
  ).
  (should "(for an-object statements ...) traverses all fields in the object and returns final result." (=> ()
    (assert null (for (@:) (++ a).
    (assert 1 (for (@ x: 1) (++ b).
    (assert 2 (for (@ x: 1, y: 2) (++ c).
    (assert 3 (for (@ x: 1, y: 2, z: 3) (++ d).
  ).
).

(define "(for ... in ...)" (= ()
  (should "(for value in) returns null." (=> ()
    (assert null (for x in).
    (assert null (for (x y) in).
    (assert null (for (x y z) in).
  ).
  (should "(for value in a-range) returns null." (=> ()
    (assert null (for x in (1 10).
    (assert null (for (x y) in (1 10).
    (assert null (for (x y z) in (1 10).
  ).
  (should "(for value in an-array statements ...) traverses all values in the array and returns final result." (=> ()
    (var a 0)
    (assert 25 (for x in (@ 1 3 5 7 9) (a += x).
    (assert 25 a)
  ).
  (should "(for (value offset) in an-array statements ...) traverses all values and their offsets in the array and returns final result." (=> ()
    (var a 0)
    (assert 40 (for (x i) in (@ 1 3 5 7 9) (a += x i 1).
    (assert 40 a)
  ).
  (should "(for field in an-object statements ...) traverses all field names of the object and returns final result." (=> ()
    (var a "")
    (assert "xyz" (for name in (@ x: 1 y: 2 z: 3) (a += name).
    (assert "xyz" a)
  ).
  (should "(for (field value) in an-object statements ...) traverses all fields and their values in the object and returns final result." (=> ()
    (var a "")
    (assert "x:1 y:2 z:3 " (for (name value) in (@ x: 1 y: 2 z: 3) (a += name ":" value " ").
    (assert "x:1 y:2 z:3 " a)
  ).
  (should "(for value in iterable statements ...) traverses all values returned by the iterable entity and returns the final result." (=> ()
    (var iter (=:()
      (var pairs (@ (@ "x" 1) (@ "y" 2) (@ "z" 3).
      (var offset 0)
      (=>() (if (offset < 3) (pairs (offset ++).
    ).
    (var a "")
    (assert "xyz" (for name in iter (a += name).
    (assert "xyz" a)
  ).
  (should "(for (values ...) in iterable statements ...) traverses all values and tries to populate them and returns the final result." (=> ()
    (var iter (=:()
      (var pairs (@ (@) (@ "x") (@ "y" 2) (@ "z" 3 4).
      (var offset 0)
      (=>() (if (offset < 4) (pairs (offset ++).
    ).
    (var a (@).
    (assert 12 (for (x y z) in iter (a push x y z) (a length).
    (assert null (a 0).
    (assert null (a 1).
    (assert null (a 2).

    (assert "x" (a 3).
    (assert null (a 4).
    (assert null (a 5).

    (assert "y" (a 6).
    (assert 2 (a 7).
    (assert null (a 8).

    (assert "z" (a 9).
    (assert 3 (a 10).
    (assert 4 (a 11).
  ).
  (should "(break value) applies value as the result of for loop." (=> ()
    (var i 0)
    (assert 10 (for i in (1 10) (++ i) (if (i > 5) (break 10).
    (assert 6 i)
  ).
  (should "(break values ...) applies the array of values as the result of for loop." (=> ()
    (var i 0)
    (var result (for i in (1 10) (++ i) (if (i > 5) (break 10 100).
    (assert 6 i)
    (assert (result is-an array).
    (assert 10 (result 0).
    (assert 100 (result 1).
  ).
).