(var * (load "./share/type" (@ the-type: lambda).

(define "Lambda Common Behaviors" (=> ()
  (define "Identity" (= ()
    (should "an empty lambda without parameters is always the same." (= ()
      (var l1 (=).
      (var l2 (= ().
      (var l3 (= x).
      (var l4 (= (x).
      (assert ($l1 is-a lambda).
      (assert ($l2 is-a lambda).
      (assert ($l3 is-a lambda).
      (assert ($l4 is-a lambda).
      (assert ($l1 is l2).
      (assert false ($l1 is-not l2).

      (assert ($l1 is-not l3).
      (assert ($l2 is-not l3).
      (assert ($l1 is-not l4).
      (assert ($l2 is-not l4).

      (assert ($l3 is-not l4).
      (assert ($l4 is-not l3).
    ).
    (should "non-empty lambda code generates different lambdas in each evaluation." (= ()
      (var code (` (= x x).
      (var l1 (code).
      (var l2 (code).
      (assert ($l1 is-a lambda).
      (assert ($l2 is-a lambda).
      (assert ($l1 is-not l2).
      (assert false ($l1 is l2).
    ).
  ).

  (define "Equivalence" (= ()
    (should "all bound lambda are equivalent with their original bound target and each others." (= ()
      (var l (=() this).
      (var l1 ($l bind 1).
      (var l2 ($l bind 2).

      (assert null (l).
      (assert 1 (l1).
      (assert 2 (l2).

      (assert ($l is-a lambda).
      (assert ($l1 is-a lambda).
      (assert ($l2 is-a lambda).

      (assert ($l equals l).
      (assert false ($l not-equals l).

      (assert ($l equals l1).
      (assert false ($l not-equals l1).

      (assert ($l1 equals l).
      (assert false ($l1 not-equals l).

      (assert ($l1 equals l2).
      (assert false ($l1 not-equals l2).
    ).
  ).

  (define "Ordering" (= ()
    (should "comparing a lambda with itself returns 0." (= ()
      (var l (= x x).
      (assert ($l is-a lambda).
      (assert 0 ($l compares-to l).
      (assert 0 ($(lambda empty) compares-to (lambda empty).
    ).
    (should "comparison of two lambdas returns null." (=> ()
      (var l1 (= () null).
      (var l2 (= () null).
      (assert ($l1 is-a lambda).
      (assert ($l2 is-a lambda).
      (assert null ($l1 compares-to l2).

      (let l1 (= x x).
      (let l2 (= x x).
      (assert ($l1 is-a lambda).
      (assert ($l2 is-a lambda).
      (assert null ($l1 compares-to l2).
    ).
  ).

  (define "Emptiness" (= ()
    (should "a lambda is defined as empty when its body is empty." (= ()
      (assert ($(=) is-empty).
      (assert false ($(=) not-empty).

      (assert ($(= x) is-empty).
      (assert false ($(= x) not-empty).

      (assert ($(= (x y)) is-empty).
      (assert false ($(= (x y)) not-empty).

      (assert false ($(= () null) is-empty).
      (assert ($(= () null) not-empty).

      (assert false ($(= () 0) is-empty).
      (assert ($(= () 0) not-empty).

      (assert false ($(= x x) is-empty).
      (assert ($(= x x) not-empty).

      (assert false ($(= (x y) (+ x y)) is-empty).
      (assert ($(= (x y) (+ x y)) not-empty).
    )
  ).

  (define "Encoding" (=> ()
    (should "a lambda is encoded to its code." (=> ()
      (for value
          in (the-values concat (lambda empty).
        (var code ($value to-code).
        (assert (code is-a tuple).
        (assert 3 (code length).
        (assert (symbol lambda) (code 0).
        (assert (((code 1) is-a tuple) ?
          ((code 1) not-plain)
          ((code 1) is-a symbol)
        ).
        (assert ((code 2) is-a tuple).
        (assert ((code 2) is-plain).
      ).
    ).
  ).

  (define "Representation" (=> ()
    (should "(lambda empty) is represented as (= ())." (= ()
      (assert "(= ())" ($(lambda empty) to-string).
    ).
    (should "a lambda is represented as its string value of its code." (=> ()
      (for value
          in (the-values concat (lambda empty).
        (assert ($value is-a lambda).
        (var code ($value to-code).
        (assert (code to-string) ($value to-string).
      ).
    ).
  ).
).

(define "Constant Value" (= ()
  (define "(lambda \"noop\")" (= ()
    (should "(lambda \"noop\") is a lambda with empty parameters and an empty body." (= ()
      (assert ($(lambda "noop") is-a lambda).
      (assert false (lambda "noop":: is-static).
      (assert "noop" ($(lambda "noop") name).

      (assert (($(lambda "noop") parameters) is-a tuple).
      (assert (($(lambda "noop") parameters) not-plain).
      (assert 0 (($(lambda "noop") parameters) length).

      (assert (($(lambda "noop") body) is-a tuple).
      (assert (($(lambda "noop") body) is-plain).
      (assert 0 (($(lambda "noop") parameters) length).
    ).
    (should "(lambda \"noop\") always return null." (= ()
      (assert null (lambda noop).
      (var noop (lambda "noop").
      (assert null (noop).
    ).
    (should "(lambda \"noop\") is encoded to (tuple lambda)." (= ()
      (assert (($(lambda "noop") to-code) is (tuple lambda).
    ).
  ).
  (define "(lambda \"static\")" (= ()
    (should "(lambda \"static\") is a static lambda with empty parameters and an empty body." (= ()
      (assert (lambda "static":: is-a lambda).
      (assert (lambda "static":: is-static).
      (assert "static" (lambda "static":: name).

      (assert (($(lambda "static") parameters) is-a tuple).
      (assert (($(lambda "static") parameters) not-plain).
      (assert 0 (($(lambda "static") parameters) length).

      (assert (($(lambda "static") body) is-a tuple).
      (assert (($(lambda "static") body) is-plain).
      (assert 0 (($(lambda "static") parameters) length).
    ).
    (should "(lambda \"static\") always return null." (= ()
      (assert null (lambda static).
      (var static (lambda "static").
      (assert null (static).
    ).
    (should "(lambda \"static\") is encoded to (tuple stambda)." (= ()
      (assert (($(lambda "static") to-code) is (tuple stambda).
    ).
  ).
).

(define "(lambda empty)" (= ()
  (should "(lambda \"empty\") is a generic lambda." (= ()
    (assert ($(lambda "empty") is-a lambda).
    (assert "empty" ($(lambda "empty") name).

    (assert ($(lambda "empty") is-generic).
    (assert false ($(lambda "empty") not-generic).
  ).
  (should "(lambda empty) returns (lambda \"noop\")." (= ()
    (assert ($(lambda empty) is (lambda "noop").

    (var empty (lambda "empty").
    (assert ($(empty) is (lambda "noop").
  ).
).

(define "(lambda of)" (= ()
  (should "(lambda of) is only a placeholder generator and actually an alias of (lambda empty)." (= ()
    (assert ($(lambda of) is (lambda empty).
  ).
  (should "a lambda can be dynamically generated by evaluating a tuple." (= ()
    (var c "value: ")
    (var t (tuple of (symbol lambda) (`x) (`((c ?? ": ") + x).
    (var f (t).
    (assert ($f is-a lambda).
    (assert ": null" (f).
    (assert ": true" (f true).
    (assert ": 100" (f 100).
  ).
  (should "a lambda can also be dynamically generated by explicitly evaluating a tuple." (= ()
    (var c "value: ")
    (var t (tuple of (symbol lambda) (`x) (`((c ?? ": ") + x).
    (var f (eval t).
    (assert ($f is-a lambda).
    (assert ": null" (f).
    (assert ": true" (f true).
    (assert ": 100" (f 100).
  ).
).

(define "($a-lambda name)" (= ()
  (should "($a-lambda name) returns (string empty) for an anonymous lambda." (= ()
    (assert "" ($(= x) name).
  ).
  (should "($a-lambda name) returns the lambda's name." (= ()
    (var l (= x).
    (var ll l).
    (assert "l" ($l name).
    (assert "l" ($ll name).
  ).
).

(define "($a-lambda parameters)" (= ()
  (should "return (tuple empty) for a lambda without any parameter." (= ()
    (assert (($(= () null) parameters) is (tuple empty).
  ).
  (should "return a tuple when the lambda has only one parameter." (= ()
    (assert (quote x) ($(= x) parameters).
    (assert (quote x) ($(= x x) parameters).
    (assert (quote x) ($(= (x)) parameters).
    (assert (quote x) ($(= (x) x) parameters).
  ).
  (should "return a tuple when the lambda has multiple parameters." (= ()
    (assert (quote x y) ($(= (x y)) parameters).
    (assert (quote x y) ($(= (x  y) (+ x y)) parameters).
  ).
).

(define "($a-lambda body)" (= ()
  (should "($a-lambda body) returns (tuple blank) for an empty lambda." (= ()
    (assert (($(=) body) is (tuple blank).
    (assert (($(= ()) body) is (tuple blank).
    (assert (($(= x) body) is (tuple blank).
  ).
  (should "($a-lambda body) returns a plain tuple when the lambda is not empty." (= ()
    (assert ((`(null)) as-plain) ($(= () null) body).
    (assert ((`((+ x y))) as-plain) ($(= (x  y) (+ x y)) body).
    (assert ((`((var z 100 )(+ x y  z))) as-plain) ($(= (x  y) (var z 100) (+ x y z)) body).
  ).
).

(define "($a-lambda is-static)" (= ()
  (should "($a-lambda is-static) returns true if it's a stambda - static lambda." (= ()
    (assert ($(-> () null) is-static).
    (assert ($(-> x x) is-static).
    (assert ($(-> (x) x) is-static).
  ).
  (should "($a-lambda is-static) returns false for a common lambda." (= ()
    (assert false ($(= () null) is-static).
    (assert false ($(= x) is-static).
    (assert false ($(= x x) is-static).
    (assert false ($(= (x y)) is-static).
    (assert false ($(= (x y) (+ x y)) is-static).
  ).
  (should "a stambda has not this, arguments, do." (= ()
    (let ctx (->:() (@ this arguments do).
    (assert (ctx is-an array).
    (assert 3 (ctx length).
    (assert null (ctx 0).
    (assert null (ctx 1).
    (assert null (ctx 2).
  ).
  (should "a stambda only allows one argument at most." (= ()
    (var args (-> 10:x (@ 1 x).
    (assert (args is-an array).
    (assert 2 (args length).
    (assert 1 (args 0).
    (assert 10 (args 1).

    (let args (->(1 2):(x y) (@ y x).
    (assert (args is-an array).
    (assert 2 (args length).
    (assert null (args 0).
    (assert 1 (args 1).
  ).
  (should "a stambda intercepts redo as return." (= ()
    (assert 4 (-> 5:x (x > 0:: ? (redo (x - 1)) x).
  ).
  (should "a stambda has no access to -app and -module." (= ()
    (var ctx (=:() (@ 1 -app -module).
    (assert (ctx is-an array).
    (assert 3 (ctx length).
    (assert 1 (ctx 0).
    (assert (ctx 1:: is-a string).
    (assert (ctx 2:: is-a string).

    (let ctx (->:() (@ 1 -app -module).
    (assert (ctx is-an array).
    (assert 3 (ctx length).
    (assert 1 (ctx 0).
    (assert null (ctx 1).
    (assert null (ctx 2).
  ).
  (should "a stambda cannot import another module." (= ()
    (var mod (=:() (import "es/test").
    (assert (mod is-an object).

    (let mod (->:() (import "es/test").
    (assert (mod is null).
  ).
  (should "a stambda has no access to (env)." (= ()
    (var values (=:() (env).
    (assert (values is-an object).

    (let values (->:() (env).
    (assert (values is null).
  ).
  (should "a stambda can choose to require for this instead of an argument." (= ()
    (var self (-> this this).
    (assert null (self 1).
    (assert 1 ($self apply 1).
  ).
  (should "a stambda can be a member of an object." (= ()
    (var obj (@ x: 1 read: (-> this x).
    (assert (obj "read":: is-static).
    (assert 1 (obj read).
  ).
  (should "a stambda can be a member of a class." (= ()
    (var cat (@:class age: 1.5 how-old: (-> this age).
    (var kitty (cat of (@ x: 10).
    (assert (kitty "how-old":: is-static).
    (assert 1.5 (kitty how-old).
  ).
).

(define "($a-lambda is-const)" (= ()
  (should "($a-lambda is-const) returns true if it's a constambda - constant lambda." (= ()
    (assert (lambda "static":: is-const).
  ).
  (should "an empty - no body - static lambda is taken as constant." (= ()
    (assert ($(->()) is-const).
    (assert ($(->() 1) is-const).
    (assert ($(-> x) is-const).
    (assert false ($(-> x x) is-const).
    (assert ($(-> this) is-const).
    (assert false ($(-> this this) is-const).
  ).
  (should "a bound stambda generates a constambda." (= ()
    (var sta (-> x x).
    (assert ($sta is-static).
    (var con ($sta bind 100).
    (assert ($con is-static).
    (assert ($con is-const).
    (assert 100 (con).

    (let sta (-> this this).
    (assert ($sta is-static).
    (var con ($sta bind 10).
    (assert ($con is-static).
    (assert ($con is-const).
    (assert 10 (con).
  ).
  (should "a constambda can be a member of an object." (= ()
    (var x 1).
    (var obj (@ x: 10 read: (->() (100 + x).
    (assert (obj "read":: is-static).
    (assert (obj "read":: is-const).
    (assert 100 (obj read).
  ).
  (should "a constambda can be a member of a class." (= ()
    (var age 0.5).
    (var cat (@:class age: 1.5 how-old: (->() (10 + age).
    (var kitty (cat of (@ age: 2.5).
    (assert (kitty "how-old":: is-static).
    (assert (kitty "how-old":: is-const).
    (assert 10 (kitty how-old).
  ).
).

(define "($a-lambda is-generic)" (= ()
  (should "($a-lambda is-generic) returns true for most type & instance methods." (= ()
    (assert ($($(=) "apply") is-a lambda).
    (assert ($($(=) "apply") is-generic).

    (assert ($($(=) "bind") is-a lambda).
    (assert ($($(=) "bind") is-generic).
  ).
  (should "($a-lambda is-generic) returns false for lambdas generated by code." (= ()
    (assert false ($(= () null) is-generic).
    (assert false ($(= x) is-generic).
    (assert false ($(= x x) is-generic).
    (assert false ($(= (x y)) is-generic).
    (assert false ($(= (x y) (+ x y)) is-generic).
  ).
).

(define "($a-lambda not-generic)" (= ()
  (should "($a-lambda not-generic) returns false for some runtime lambdas." (= ()
    (assert ($($(=) "apply") is-a lambda).
    (assert false ($($(=) "apply") not-generic).

    (assert ($($(=) "bind") is-a lambda).
    (assert false ($($(=) "bind") not-generic).
  ).
  (should "($a-lambda not-generic) returns true for lambdas generated by code." (= ()
    (assert ($(= () null) not-generic).
    (assert ($(= x) not-generic).
    (assert ($(= x x) not-generic).
    (assert ($(= (x y)) not-generic).
    (assert ($(= (x y) (+ x y)) not-generic).
  ).
).

(define "($a-lambda is-bound)" (= ()
  (should "($a-lambda is-bound) returns false if the lambda has not been bound with a subject." (= ()
    (assert false ($(= () null) is-bound).
    (assert false ($(= x (x ++)) is-bound).
  ).
  (should "($a-lambda is-bound) returns true if the lambda is bound with a subject." (= ()
    (var s (@ y: 1).
    (assert ($($(= () null) bind s) is-bound).
    (assert ($($(= x (x ++)) bind s) is-bound).
  ).
).

(define "($a-lambda not-bound)" (= ()
  (should "($a-lambda not-bound) returns true for a free lambda." (= ()
    (assert ($(= () null) not-bound).
    (assert ($(= x (x ++)) not-bound).
  ).
  (should "($a-lambda not-bound) returns false for a bound lambda." (= ()
    (var s (@ y: 1).
    (assert false ($($(= () null) bind s) not-bound).
    (assert false ($($(= x (x ++)) bind s) not-bound).
  ).
).

(define "($a-lambda this)" (= ()
  (should "($a-lambda this) returns null for a free lambda." (= ()
    (assert null ($(= () null) this).
    (assert null ($(= x (x ++)) this).
  ).
  (should "($a-lambda this) returns null if it's bound to null." (= ()
    (var l ($(= () null) bind null).
    (assert ($l is-bound).
    (assert null ($l this).

    (let l ($(= x (x ++)) bind null).
    (assert ($l is-bound).
    (assert null ($l this).
  ).
  (should "($a-lambda this) returns the bound subject if it's bound." (= ()
    (var s (@ x: 1).
    (var l ($(= () null) bind s).
    (assert ($l is-bound).
    (assert s ($l this).

    (let l ($(= x (x ++)) bind s).
    (assert ($l is-bound).
    (assert s ($l this).
  ).
).

(define "($a-lambda apply ...)" (= ()
  (should "($a-lambda apply) call the lambda with null as this and an empty argument list." (= ()
    (var l (= x
      (assert null this)
      (assert 0 (arguments length).
    ).
    ($l apply).
  ).
  (should "($a-lambda apply this-value) call the lambda with this-value as this." (= ()
    (var obj (@ x: 1).
    (var l (= x
      (assert 0 (arguments length).
      (return this)
    ).
    (assert obj ($l apply obj).
  ).
  (should "($a-lambda apply this-value args) call the lambda with this-value as this and elements in args as arguments." (= ()
    (var obj (@ x: 1).
    (var l (= (x y)
      (assert 1 x)
      (assert 2 y)
      (assert 3 (arguments length).
      (assert 1 (arguments 0).
      (assert 2 (arguments 1).
      (assert 3 (arguments 2).
      (return this)
    ).
    (assert obj ($l apply obj (@ 1 2 3).
  ).
  (should "($a-lambda apply this-value value) call the lambda with this-value as this and value as the only argument if value is not an array." (= ()
    (var obj (@ x: 1).
    (var l (= (x y)
      (assert 1 x)
      (assert null y)
      (assert 1 (arguments length).
      (assert 1 (arguments 0).
      (return this)
    ).
    (assert obj ($l apply obj 1 true "x").
  ).
).

(define "($a-lambda bind ...)" (= ()
  (should "($a-lambda bind) implicitly binds the original lambda with null." (= ()
    (var l (= x (+ 1 x).
    (var b ($l bind).
    (assert l b).
    (assert ($b equals l).
    (assert false ($b is l).

    (assert ($b is-bound).
    (assert null ($b this).
  ).
  (should "($a-lambda bind null) explicitly binds the original lambda with null." (= ()
    (var s (@ y: 100).
    (var l (= () this).
    (assert false ($l is-bound).
    (assert ($l not-bound).
    (assert null ($l this).
    (assert s (s ($l).

    (var b ($l bind null).
    (assert ($b is-a lambda).
    (assert ($b is-not l).
    (assert ($b is-bound).
    (assert false ($b not-bound).
    (assert null ($b this).
    (assert null (b ($l).
  ).
  (should "($a-lambda bind subject) returns a bound lambda whose this is fixed to subject." (= ()
    (var s1 (@ y: 100).
    (var l (= x this).
    (assert false ($l is-bound).
    (assert ($l not-bound).
    (assert null ($l this).
    (assert s1 (s1 ($l).

    (var b ($l bind s1).
    (assert ($b is-a lambda).
    (assert ($b is-not l).
    (assert ($b is-bound).
    (assert false ($b not-bound).
    (assert s1 ($b this).

    (var s2 (@ y: 10).
    (assert s1 (s2 ($b).
  ).
  (should "($a-bound-lambda bind new-subject) returns the original bound lambda." (= ()
    (var s1 (@ y: 100).
    (var l (= x this).
    (let l ($l bind s1).

    (assert ($l is-a lambda).
    (assert ($l is-bound).
    (assert false ($l not-bound).
    (assert s1 ($l this).

    (var s2 (@ y: 1000).
    (assert l ($l bind s2).
    (assert s1 ($l this).
    (assert s1 (s2 ($l).
  ).
).

(define "direct evaluation" (= ()
  (should "(a-lambda value ...) evaluates the lambda with null as this and all argument values." (= ()
    (var l (= x
      (assert ($do is-a lambda).
      (assert null this)
      (assert true x)
      (assert 10 (arguments length).
      (assert true (arguments 0).
      (assert null (arguments 1).
      (assert 1 (arguments 2).
      (assert "x" (arguments 3).
      (assert (range empty) (arguments 4).
      (assert (symbol empty) (arguments 5).
      (assert (tuple empty) (arguments 6).
      (assert (operator empty) (arguments 7).
      (assert (lambda empty) (arguments 8).
      (assert (function empty) (arguments 9).
    ).
    (l true null 1 "x" (range empty) (symbol empty) (tuple empty) (operator empty) (lambda empty) (function empty).
  ).
  (should "(s ($a-lambda) value ...) evaluates the lambda with s as this and all argument values." (= ()
    (var obj (@ x: 1).
    (var l (= x
      (assert ($do is-a lambda).
      (return this).
      (assert true x).
      (assert 10 (arguments length).
      (assert true (arguments 0).
      (assert null (arguments 1).
      (assert 1 (arguments 2).
      (assert "x" (arguments 3).
      (assert (range empty) (arguments 4).
      (assert (symbol empty) (arguments 5).
      (assert (tuple empty) (arguments 6).
      (assert (operator empty) (arguments 7).
      (assert (lambda empty) (arguments 8).
      (assert (function empty) (arguments 9).
    ).
    (assert l ($l).
    (assert ($($l) is l).
    (var result (obj ($l) true null 1 "x" (range empty) (symbol empty) (tuple empty) (operator empty) (lambda empty) (function empty).
    ((result is obj) ? null (result ?? (assert obj result)).
  ).
  (should "(s (= ...) value ...) evaluates the anonymous lambda with s as this and all argument values." (= ()
    (var obj (@ x: 1).
    (var result
      (obj
        (= x
          (assert ($do is-a lambda).
          (return this).
          (assert true x)
          (assert 10 (arguments length).
          (assert true (arguments 0).
          (assert null (arguments 1).
          (assert 1 (arguments 2).
          (assert "x" (arguments 3).
          (assert (range empty) (arguments 4).
          (assert (symbol empty) (arguments 5).
          (assert (tuple empty) (arguments 6).
          (assert (operator empty) (arguments 7).
          (assert (lambda empty) (arguments 8).
          (assert (function empty) (arguments 9).
        ).
        true null 1 "x" (range empty) (symbol empty) (tuple empty) (operator empty) (lambda empty) (function empty)
      ).
    ).
    ((result is obj) ? null (result ?? (assert obj result)).
  ).
).

(define "anonymous evaluation" (= ()
  (should "(=:() ...) evaluates the anonymous lambda with null as this and no argument." (= ()
    (=:()
      (assert ($do is-a lambda).
      (assert null this)
      (assert 0 (arguments length).
    ).
  ).
  (should "(=():() ...) evaluates the anonymous lambda with null as this and no argument." (= ()
    (=():()
      (assert ($do is-a lambda).
      (assert null this)
      (assert null x)
      (assert 0 (arguments length).
    ).
  ).
  (should "(=:() ...) evaluates the anonymous lambda with null as this and no argument." (= ()
    (=:()
      (assert ($do is-a lambda).
      (assert null this)
      (assert 0 (arguments length).
    ).
  ).
  (should "(=:x ...) evaluates the anonymous lambda with null as this and x as an argument." (= ()
    (var x 100)
    (=:x
      (assert ($do is-a lambda).
      (assert null this)
      (assert 100 x)
      (assert 1 (arguments length).
    ).
  ).
  (should "(=:(x, y) ...) evaluates the anonymous lambda with null as this and both x and y as arguments." (= ()
    (var x 100)
    (var y 200)
    (=:(x, y)
      (assert ($do is-a lambda).
      (assert null this)
      (assert 100 x)
      (assert 200 y)
      (assert 2 (arguments length).
    ).
  ).
  (should "(=():x ...) evaluates the anonymous lambda with null as this and no argument." (= ()
    (=():x
      (assert ($do is-a lambda).
      (assert null this)
      (assert null x)
      (assert 0 (arguments length).
    ).
  ).
  (should "(=():(x ...) ...) evaluates the anonymous lambda with null as this and no argument." (= ()
    (=():(x y)
      (assert ($do is-a lambda).
      (assert null this)
      (assert null x)
      (assert null y)
      (assert 0 (arguments length).
    ).
  ).
  (should "(=(value ...):x ...) evaluates the anonymous lambda with null as this and all argument values." (= ()
    (=
      (true null 1 "x" (range empty) (symbol empty) (tuple empty) (operator empty) (lambda empty) (function empty).
    : x
      (assert ($do is-a lambda).
      (assert null this)
      (assert true x)
      (assert 10 (arguments length).
      (assert true (arguments 0).
      (assert null (arguments 1).
      (assert 1 (arguments 2).
      (assert "x" (arguments 3).
      (assert (range empty) (arguments 4).
      (assert (symbol empty) (arguments 5).
      (assert (tuple empty) (arguments 6).
      (assert (operator empty) (arguments 7).
      (assert (lambda empty) (arguments 8).
      (assert (function empty) (arguments 9).
    ).
  ).
  (should "(=(value ...):(x ...) ...) evaluates the anonymous lambda with null as this and all argument values." (= ()
    (=
      (true null 1 "x" (range empty) (symbol empty) (tuple empty) (operator empty) (lambda empty) (function empty).
    : (x y z)
      (assert ($do is-a lambda).
      (assert null this)
      (assert true x)
      (assert null y)
      (assert 1 z)
      (assert 10 (arguments length).
      (assert true (arguments 0).
      (assert null (arguments 1).
      (assert 1 (arguments 2).
      (assert "x" (arguments 3).
      (assert (range empty) (arguments 4).
      (assert (symbol empty) (arguments 5).
      (assert (tuple empty) (arguments 6).
      (assert (operator empty) (arguments 7).
      (assert (lambda empty) (arguments 8).
      (assert (function empty) (arguments 9).
    ).
  ).
).

(define "(do ...): recursive call" (= ()
  (should "variable 'do' refers to current callee function." (= ()
    (var l (= ()
      (assert ($do is-a lambda).
      (assert null this).
    ).
    (l)
  ).
  (should "'do' can be used to implementation recursive call in a function." (= ()
    (assert 5050 (= 100:x
      ((x <= 1) ? x
        (x + (do (x - 1).
      ).
    ).
    (var sum (= x
      ((x <= 1) ? x
        (x + (do (x - 1).
      ).
    ).
    (assert 5050 (sum 100).
  ).
).

(define "(redo ...): tail recursion elimination" (= ()
  (should "'redo' is a special global operator, so is a pure symbol." (= ()
    (var f (= ()
      (assert ($redo is redo).
      (assert ($redo is (`redo)).
      (assert null this).
    ).
    (f)
  ).
  (should "'redo' can be used to eliminate tail recursion call." (= ()
    (assert 50005000 (= 10000: (x base)
      ((x <= 1) ? (x + base)
        (redo (x - 1) (x + base).
      ).
    ).
    (var sum (= (x base)
      ((x <= 1) ? (x + base)
        (redo (x - 1) (x + base).
      ).
    ).
    (assert 50005000 (sum 10000).
  ).
).

(define "resolve lambda context symbols" (= ()
  (should "'this' is resolved to the subject value of calling expression." (= ()
    (var l (= () (+ this 2).
    (assert "null2" (l).
    (assert "null2" (l 1).
    (assert 3 (1 ($l).
    (assert 3 (1 ($l) 2).
    (assert "x2" ("x" ($l).
    (assert "x2" ("x" ($l) 2 "y").
  ).
  (should "'arguments' is resolved according to the arguments used in calling current lambda." (= ()
    (var l (= () arguments).
    (assert 0 ((l) length).
    (assert null ((l) 0).
    (assert 1 ((l 2) length).
    (assert 2 ((l 2) 0).
    (assert null ((l 2) 1).
    (assert 2 ((l 2 "x") length).
    (assert 2 ((l 2 "x") 0).
    (assert "x" ((l 2 "x") 1).
    (assert null ((l 2 "x") 2).
  ).
  (should "'do' is resolved to the calling lambda itself." (= ()
    (var l (= () do).
    (assert ($(l) is l).
    (assert ($(1 ($l)) is l).
    (assert ($("x" ($l) 2) is l).
    (assert ($((@) ($l) 2 "x") is l).
  ).
).

(define "resolve other symbols" (= ()
  (should "a lambda is independent of its creating scope." (= ()
    (var x 100)
    (assert 110 (=:() (10 * (x ?? 11).
  ).
  (should "other symbols are resolved in lambda's scope." (= ()
    (var x 120)
    (assert null (=:() x).
    (assert 200 (=(20):(x) (10 * x).
    (assert 6000 (=(20 30):(x y) (10 * x y).
  ).
).

(define "(var ...): variable declaration" (= ()
  (should "(var \"x\" value) defines a new local variable 'x' in current lambda's scope." (= ()
    (var x 1)

    (assert 10 (=:() (var x 10) x).
    (assert 1 x)

    (assert 100 (=:()
      (var x 100)
      (=:() (var x 101).
      x
    ).
    (assert 1 x)

    (assert 1000 (=:()
      (var x 1000)
      (=:() (=:() (var x 1001).
      x
    ).
    (assert 1 x)

    (assert 100 (=>:()
      (var x 100)
      (=:() (var x 101).
      x
    ).
    (assert 1 x)

    (assert 1000 (=>:()
      (var x 1000)
      (=:() (=:() (var x 1001).
      x
    ).
    (assert 1 x)
  ).
  (should "(var \"x\" value) can update an existing local variable 'x' in current lambda's scope." (= ()
    (var x 1)

    (assert 10 (=(x):(x) (var x (x * 10)) x).
    (assert 1 x)

    (assert 10 (=:()
      (var x 1)
      (var x (x * 10).
      x
    ).
    (assert 1 x)

    (assert 10 (=:()
      (let x 1)
      (var x (x * 10).
      x
    ).
    (assert 1 x)
  ).
).

(define "(let ...): value assignment" (= ()
  (should "(let \"x\" value) defines a new local variable 'x' in current lambda's scope." (= ()
    (var x 1)

    (assert 10 (=:() (let x 10) x).
    (assert 1 x)

    (assert 100 (=:()
      (var x 100)
      (=:() (let x 101).
      x
    ).
    (assert 1 x)

    (assert 100 (=:()
      (let x 100)
      (=:() (let x 101).
      x
    ).
    (assert 1 x)

    (assert 1000 (=:()
      (var x 1000)
      (=:() (=:() (let x 1001).
      x
    ).
    (assert 1 x)

    (assert 1000 (=:()
      (let x 1000)
      (=:() (=:() (let x 1001).
      x
    ).
    (assert 1 x)

    (assert 100 (=>:()
      (var x 100)
      (=:() (let x 101).
      x
    ).
    (assert 1 x)

    (assert 1000 (=>:()
      (var x 1000)
      (=:() (=:() (let x 1001).
      x
    ).
    (assert 1 x)
  ).
  (should "(let \"x\" value) can update an existing local variable 'x' in current lambda's scope." (= ()
    (var x 1)

    (assert 10 (=(x):(x) (let x (x * 10)) x).
    (assert 1 x)

    (assert 10 (=:()
      (var x 1)
      (let x (x * 10).
      x
    ).
    (assert 1 x)

    (assert 10 (=:()
      (let x 1)
      (let x (x * 10).
      x
    ).
    (assert 1 x)
  ).
).

(define "(local retval ...)" (= ()
  (should "(local retval) defines the default return value as null." (= ()
    (assert null (=:() (local retval) 200).
    (assert null (->:() (local retval) 200).
  ).
  (should "(local retval value) defines the default return value as value." (= ()
    (assert null (=:() (local retval null) 200).
    (assert null (->:() (local retval null) 200).

    (assert 200 (=:() (var retval null) 200).
    (assert 200 (->:() (var retval null) 200).

    (assert type (=:() (local retval type) 200).
    (assert type (->:() (local retval type) 200).

    (assert 200 (=:() (var retval type) 200).
    (assert 200 (->:() (var retval type) 200).

    (assert true (=:() (local retval true) 200).
    (assert true (->:() (local retval true) 200).

    (assert 200 (=:() (var retval true) 200).
    (assert 200 (->:() (var retval true) 200).

    (assert false (=:() (local retval false) 200).
    (assert false (->:() (local retval false) 200).

    (assert 200 (=:() (var retval false) 200).
    (assert 200 (->:() (var retval false) 200).

    (assert 1 (=:() (local retval 1) 200).
    (assert 1 (->:() (local retval 1) 200).

    (assert 200 (=:() (var retval 1) 200).
    (assert 200 (->:() (var retval 1) 200).

    (assert 0 (=:() (local retval 0) 200).
    (assert 0 (->:() (local retval 0) 200).

    (assert 200 (=:() (var retval 0) 200).
    (assert 200 (->:() (var retval 0) 200).

    (assert -1 (=:() (local retval -1) 200).
    (assert -1 (->:() (local retval -1) 200).

    (assert 200 (=:() (var retval -1) 200).
    (assert 200 (->:() (var retval -1) 200).
  ).
  (should "default return value can be overridden by an explicit (return value)." (= ()
    (assert 200 (=:() (local retval null) (return 200).
    (assert 200 (->:() (local retval null) (return 200).

    (assert 200 (=:() (local retval type) (return 200).
    (assert 200 (->:() (local retval type) (return 200).

    (assert 200 (=:() (local retval true) (return 200).
    (assert 200 (->:() (local retval true) (return 200).

    (assert 200 (=:() (local retval false) (return 200).
    (assert 200 (->:() (local retval false) (return 200).

    (assert 200 (=:() (local retval 1) (return 200).
    (assert 200 (->:() (local retval 1) (return 200).

    (assert 200 (=:() (local retval 0) (return 200).
    (assert 200 (->:() (local retval 0) (return 200).

    (assert 200 (=:() (local retval -1) (return 200).
    (assert 200 (->:() (local retval -1) (return 200).
  ).
).