(var (types) (import (samples) from "./samples/types").

(define "Identity" (=> ()
  (should "null is and only is itself." (=> ()
    (assert (null is).
    (assert (null is null).
    (assert false (null is-not).
    (assert false (null is-not null).

    (assert false (null is type).
    (assert (null is-not type).

    (for t in types
      (assert false (null is (t the-type).
      (assert (null is-not (t the-type).

      (assert false (null is (t "empty").
      (assert (null is-not (t "empty").

      (for v in (t values)
        (assert false (null is v).
        (assert (null is-not v).
      ).
).

(define "Identity Operators" (= ()
  (should "'===' is 'is'." (= ()
    (assert ($(null "===") is (null "is").
  ).
  (should "'!==' is 'is-not'." (= ()
    (assert ($(null "!==") is (null "is-not").
  ).
).

(define "Equivalence" (= ()
  (should "null's equivalence is identical with its identity." (= ()
    (assert ($(null "equals") is (null "is").
    (assert ($(null "not-equals") is (null "is-not").
  ).
).

(define "Equivalence Operators" (= ()
  (should "'==' is 'equals'." (= ()
    (assert ($(null "==") is (null "equals").
  ).
  (should "'!=' is 'not-equals'." (= ()
    (assert ($(null "!=") is (null "not-equals").
  ).
).

(define "Ordering" (=> ()
  (should "null is only comparable with itself." (=> ()
    (assert 0 (null compares-to).
    (assert 0 (null compares-to null).

    (assert null (null compares-to type).

    (for t in types
      (assert null (null compares-to (t the-type).
      (assert null (null compares-to (t "empty").
      (for v in (t values)
        (assert null (null compares-to v).
      ).
).

(define "Type Verification" (=> ()
  (should "null is the type of itself." (=> ()
    (assert (null is-a).
    (assert (null is-a null).
    (assert false (null is-not-a).
    (assert false (null is-not-a null).

    (assert false (null is-a type).
    (assert (null is-not-a type).

    (for t in types
      (assert false (null is-a (t the-type).
      (assert (null is-not-a (t the-type).
    ).
).

(define "Emptiness" (= ()
  (should "null is an empty value." (= ()
    (assert (null is-empty).
    (assert false (null not-empty).
).

(define "Encoding" (= ()
  (should "null is encoded to itself." (= ()
    (assert null (null to-code).
).

(define "Representation" (= ()
  (should "null is represented as 'null'." (= ()
    (assert "null" (null to-string).
).

(define "Indexer" (= ()
  (should "the indexer is a lambda." (= ()
    (assert ($(null ":") is-a lambda).
  ).
  (should "null's type is null." (= ()
    (assert null (null type).

    (assert null (null "type").
    (assert null (null (`type).

    (assert null (null :"type").
    (assert null (null :(`type).

    (assert null (null :"type" x).
    (assert null (null :(`type) x).
  ).
).

(define "Evaluation" (=> ()
  (should "null is evaluated to null." (=> ()
    (assert null (null).
    (assert null ((` ())).
    (assert null (null null).

    (assert null (null type).

    (for t in types
      (assert null (null (t the-type).
      (assert null (null (t "empty").
      (for v in (t values)
        (assert null (null v).
      ).
  ).
).

(define "Arithmetic Operators" (=> ()
  (should "(++ null) returns 1." (=> ()
    (assert 1 (++).
    (assert 1 (++ null).

    (var n null)
    (assert 1 (++ n).
    (assert 1 n).
  ).
  (should "(-- null) returns -1." (=> ()
    (assert -1 (--).
    (assert -1 (-- null).

    (var n null)
    (assert -1 (-- n).
    (assert -1 n).
  ).
).

(define "Bitwise Operators" (=> ()
  (should "(~ null) returns (~ 0)." (=> ()
    (assert (~ 0) (~).
    (assert (~ 0) (~ null).

    (var n null)
    (assert (~ 0) (~ n).
  ).
).

(define "General Operators" (=> ()
  (should "(+ null) returns 'null'." (=> ()
    (assert 0 (+).
    (assert "null" (+ null).
    (assert "nullnull" (+ null null).

    (var n null)
    (assert "null" (+ n).
    (assert "nullnull" (+ n n).
  ).
).

(define "Logical Operators" (=> ()
  (define "Logical NOT: (! null)" (=> ()
    (should "(! null) returns true." (=> ()
      (assert true (! null).

      (var n null)
      (assert true (! n).
    ).
    (should "(not null) returns true." (=> ()
      (assert true (not null).

      (var n null)
      (assert true (not n).
    ).
  ).
  (define "Logical AND: (null && ...)" (=> ()
    (should "(null &&) returns null." (=> ()
      (assert null (null &&).
      (var n null)
      (assert null (n &&).
    ).
    (should "(null && x) returns null." (=> ()
      (assert null (null && true).
      (var n null)
      (assert null (n && true).
    ).
    (should "(null && x y) returns null." (=> ()
      (assert null (null && true true).
      (var n null)
      (assert null (n && true true).
    ).
    (should "'and' is an alias of '&&'." (=> ()
      (assert (null "and") (null "&&").
      (assert (null "&&") (null "and").
    ).
  ).
  (define "logical AND Self-Assignment: (null &&= ...)" (=> ()
    (should "(null &&=) returns null." (=> ()
      (assert null (null &&=).
      (var n null)
      (assert null (n &&=).
      (assert null n)
    ).
    (should "(null &&= x) returns null." (=> ()
      (assert null (null && true).
      (var n null)
      (assert null (n &&= true).
      (assert null n)
    ).
    (should "(null &&= x y) returns null." (=> ()
      (assert null (null && true true).
      (var n null)
      (assert null (n &&= true true).
      (assert null n)
    ).
  ).
  (define "Logical OR: (null || ...)" (=> ()
    (should "(null ||) returns null." (=> ()
      (assert null (null ||).
      (var n null)
      (assert null (n ||).
    ).
    (should "(null || x) returns x." (=> ()
      (assert 1 (null || 1).
      (var n null)
      (assert 1 (n || 1).
    ).
    (should "(null || null x) returns x." (=> ()
      (assert 1 (null || null 1).
      (var n null)
      (assert 1 (n || null 1).
    ).
    (should "'or' is an alias of '||'." (=> ()
      (assert (null "or") (null "||").
      (assert (null "||") (null "or").
    ).
  ).
  (define "Logical OR Self-Assignment: (null ||= ...)" (=> ()
    (should "(null ||=) returns null." (=> ()
      (assert null (null ||=).
      (var n null)
      (assert null (n ||=).
      (assert null n)
    ).
    (should "(null ||= x) returns x." (=> ()
      (assert 1 (null ||= 1).
      (var n null)
      (assert 1 (n ||= 1).
      (assert 1 n)
    ).
    (should "(null ||= null x) returns x." (=> ()
      (assert 1 (null ||= null 1).
      (var n null)
      (assert 1 (n ||= null 1).
      (assert 1 n)
    ).
  ).
).

(define "Global Operators" (=> ()
  (define "Boolean Test: (null ? ...)" (=> ()
    (should "Booleanize: (null ?) returns false." (=> ()
      (assert false (null ?).
      (var n null)
      (assert false (n ?).
    ).
    (should "Boolean Fallback: (null ? x) returns x." (=> ()
      (assert 1 (null ? 1).
      (assert 1 (null ? (1).
      (var n null)
      (assert 1 (n ? 1).
      (assert 1 (n ? (1).
    ).
    (should "Boolean Switch: (null ? x y) returns y." (=> ()
      (var x -1)
      (var y  1)
      (assert 1 (null ? (-- x) y).
      (assert -1 x)

      (assert 2 (null ? (-- x) (++ y).
      (assert -1 x)
      (assert 2 y)
    ).
  ).
  (define "Emptiness Test: (null ?* ...)" (=> ()
    (should "Booleanize: (null ?*) returns false." (=> ()
      (assert false (null ?*).
      (var n null)
      (assert false (n ?*).
    ).
    (should "Emptiness Fallback: (null ?* x) returns x." (=> ()
      (assert 1 (null ?* 1).
      (assert 1 (null ?* (1).
      (var n null)
      (assert 1 (n ?* 1).
      (assert 1 (n ?* (1).
    ).
    (should "Emptiness Switch: (null ?* x y) returns y." (=> ()
      (var x -1)
      (var y  1)
      (assert 1 (null ?* (-- x) y).
      (assert -1 x)

      (assert 2 (null ?* (-- x) (++ y).
      (assert -1 x)
      (assert 2 y)
    ).
  ).
  (define "Null Test: (null ?? ...)", (=> ()
    (define "Booleanize Null: (null ??)" (=> ()
      (should "(null ??) returns false." (=> ()
        (assert false (null ??).

        (var n null)
        (assert false (n ??).
      ).
    ).
    (define "Null Fallback: (null ?? value)" (=> ()
      (should "(null ?? null) returns null." (=> ()
        (assert null (null ?? null).
      ).
      (should "(null ?? value) returns value." (=> ()
        (assert 1 (null ?? 1).
        (assert 2 (null ?? (++ 1).

        (var n null)
        (assert 1 (n ?? 1).
        (assert 2 (n ?? (++ 1).
      ).
    ).
    (define "Null Switch: (null ?? truthy, falsy)" (=> ()
      (should "(null ?? any-value null) returns null." (=> ()
        (assert null (null ?? null null).
        (assert null (null ?? 0 null).
        (assert null (null ?? 1 null).
        (assert null (null ?? false null).
        (assert null (null ?? true null).

        (var n null)
        (assert null (n ?? null null).
        (assert null (n ?? 0 null).
        (assert null (n ?? 1 null).
        (assert null (n ?? false null).
        (assert null (n ?? true null).
      ).
      (should "(null ?? null value) returns value." (=> ()
        (assert 2 (null ?? null 2).
        (assert 2 (null ?? (null) (2).

        (var n null)
        (assert 2 (n ?? n 2).
        (assert 2 (n ?? (n) (2).
      ).
      (should "(null ?? truthy falsy) returns falsy." (=> ()
        (let x 1)
        (let y -1)
        (assert -1 (null ?? x y).
        (assert -2 (null ?? (++ x) (-- y).

        (assert 1 x)
        (assert -2 y)
      ).
    ).
  ).
).