2016 Update

Task/Null-object/00DESCRIPTION

@@ -1,5 +1,11 @@
-'''Null''' (or '''nil''') is the computer science concept of an undefined or unbound object. Some languages have an explicit way to access the null object, and some don't. Some languages distinguish the null object from [[undefined values]], and some don't.
+'''Null''' (or '''nil''') is the computer science concept of an undefined or unbound object.
+Some languages have an explicit way to access the null object, and some don't.
+Some languages distinguish the null object from [[undefined values]], and some don't.
 
+
+;Task:
 Show how to access null in your language by checking to see if an object is equivalent to the null object.
 
+
 ''This task is not about whether a variable is defined. The task is about "null"-like values in various languages, which may or may not be related to the defined-ness of variables in your language.''
+<br><br>

Task/Null-object/00META.yaml

@@ -1,2 +1,4 @@
 ---
+category:
+- Simple
 note: Basic language learning

Task/Null-object/COBOL/null-object.cobol

@@ -0,0 +1,43 @@
+       identification division.
+       program-id. null-objects.
+       remarks. test with cobc -x -j null-objects.cob
+
+       data division.
+       working-storage section.
+       01 thing-not-thing      usage pointer.
+
+      *> call a subprogram
+      *>   with one null pointer
+      *>   an omitted parameter
+      *>   and expect void return (callee returning omitted)
+      *>   and do not touch default return-code (returning nothing)
+       procedure division.
+       call "test-null" using thing-not-thing omitted returning nothing
+       goback.
+       end program null-objects.
+
+      *> Test for pointer to null (still a real thing that takes space)
+      *>   and an omitted parameter, (call frame has placeholder)
+      *>   and finally, return void, (omitted)
+       identification division.
+       program-id. test-null.
+
+       data division.
+       linkage section.
+       01 thing-one            usage pointer.
+       01 thing-two            pic x.
+
+       procedure division using
+           thing-one
+           optional thing-two
+           returning omitted.
+
+       if thing-one equal null then
+           display "thing-one pointer to null" upon syserr
+       end-if
+
+       if thing-two omitted then
+           display "no thing-two was passed" upon syserr
+       end-if
+       goback.
+       end program test-null.

Task/Null-object/J/null-object-3.j

@@ -1,10 +1,12 @@
-   1 1 0 1#3 4 _ 5
+   1 1 0 1#3 4 _ 5           NB. use bitmask to select numbers
 3 4 5
-   I.1 1 0 1
+   I.1 1 0 1                 NB. get indices for bitmask
 0 1 3
-   0 1 3 { 3 4 _ 5
+   0 1 3 { 3 4 _ 5           NB. use indices to select numbers
 3 4 5
-   1 1 0 1 #inv 3 4 5
+   1 1 0 1 #inv 3 4 5        NB. use bitmask to restore original positions
 3 4 0 5
-   1 1 0 1 #!._ inv 3 4 5
+   1 1 0 1 #!._ inv 3 4 5    NB. specify different fill element
+3 4 _ 5
+   3 4 5 (0 1 3}) _ _ _ _    NB. use indices to restore original positions
 3 4 _ 5

Task/Null-object/Maple/null-object-1.maple

@@ -0,0 +1,7 @@
+a := NULL;
+                                                         a :=
+is (NULL = ());
+                                                         true
+if a = NULL then
+    print (NULL);
+end if;

Task/Null-object/Maple/null-object-2.maple

@@ -0,0 +1,12 @@
+b := Array([1, 2, 3, Integer(undefined), 5]);
+                                                        b := [ 1 2 3 undefined 5 ]
+numelems(b);
+                                                        5
+b := Array([1, 2, 3, Float(undefined), 5]);
+                                                        b := [ 1 2 3 Float(undefined) 5 ]
+numelems(b);
+                                                        5
+b := Array([1, 2, 3, NULL, 5]);
+                                                        b := [ 1 2 3 5 ]
+numelems(b);
+                                                        4

Task/Null-object/Oberon-2/null-object.oberon-2

@@ -0,0 +1,14 @@
+MODULE Null;
+IMPORT
+  Out;
+TYPE
+  Object = POINTER TO ObjectDesc;
+  ObjectDesc = RECORD
+  END;
+
+VAR
+  o: Object;  (* default initialization to NIL *)
+
+BEGIN
+  IF o = NIL THEN Out.String("o is NIL"); Out.Ln END
+END Null.

Task/Null-object/REBOL/null-object-2.rebol

@@ -0,0 +1,2 @@
+unset? get/any 'some-var
+unset? get 'some-var