Another update from ingydotnet^djgoku

Task/Abstract-type/AmigaE/abstract-type.amiga

@@ -0,0 +1,19 @@
+OBJECT fruit
+ENDOBJECT
+
+PROC color OF fruit IS EMPTY
+
+OBJECT apple OF fruit
+ENDOBJECT
+
+PROC color OF apple IS WriteF('red ')
+
+OBJECT orange OF fruit
+ENDOBJECT
+
+PROC color OF orange IS WriteF('orange ')
+
+PROC main()
+  DEF a:PTR TO apple,o:PTR TO orange,x:PTR TO fruit
+  FORALL({x},[NEW a, NEW o],`x.color())
+ENDPROC

Task/Abstract-type/Eiffel/abstract-type-2.e

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+note
+	title: "Prototype Person"
+	description: "Abstract notion of a {PERSON}."
+	synopsis: "[
+		Abstract Data Types as represented by any Eiffel class, fully or partially implemented, are
+		not just about the attribute and routine features of the class (deferred or implemented).
+		The class and each feature may also have specification rules expressed as preconditions,
+		post-conditions, and class invariants. Other assertion contracts may be applied to fully
+		implemented features as well.
+		
+		In the example below, while `age' is deferred (i.e. "abstract"), we have coded a rule which
+		states that any caller of `age' must only do so after a `birth_date' has been defined and
+		attached to that feature. Failing to do so will cause a contract violation. Moreover, the
+		class invariant makes two strong assertions that must always hold for any implemented version
+		of {PERSON}: The `birth_date' (if attached--that is--not Void or null) must be in the past
+		and never in the future. Also, if "Years" are used to represent the age, the calculation of
+		`age' must always agree with "current year - birth year = age".
+		
+		This form of Abstract Data Type specification has very clear advantages in that not only
+		must client code or descendents conform statically, implementing what is deferred, but they
+		must also obey the rules of the assertions dynamically in a polymorphic run-time situation.
+		]"
+
+deferred class
+	PERSON
+
+feature -- Access
+
+	first_name,
+	last_name,
+	middle_name,
+	suffix: STRING
+
+	birth_date: detachable DATE
+			-- Date-of-Birth for Current {PERSON}.
+		deferred
+		end
+
+feature -- Basic Operations
+
+	age: NATURAL_64
+			-- Age of Current {PERSON} in some undefined units.
+		require
+			has_birth_date: attached birth_date
+		deferred
+		end
+
+	age_units: STRING
+			-- Unit-of-Measure (UOM) of `age'.
+		attribute
+			Result := year_unit_string
+		end
+
+	year_unit_string: STRING = "Years"
+
+invariant
+	not_future: attached birth_date as al_birth_date implies al_birth_date < (create {DATE}.make_now)
+	accurate_age: attached birth_date as al_birth_date and then age > 0 and then age_units.same_string (year_unit_string)
+					implies ((create {DATE}.make_now).year - al_birth_date.year) = age
+
+end

Task/Abstract-type/Forth/abstract-type-2.fth

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+include FMS-SI.f
+
+The FMS object extension uses duck typing and so has no need for abstract types.

Task/Abstract-type/Fortran/abstract-type.f

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+   ! abstract derived type
+   type, abstract :: TFigure
+      real(rdp) :: area
+   contains
+      ! deferred method i.e. abstract method =  must be overridden in extended type
+      procedure(calculate_area), deferred, pass :: calculate_area
+   end type TFigure
+   ! only declaration of the abstract method/procedure for TFigure type
+   abstract interface
+      function  calculate_area(this)
+         import TFigure !imports TFigure type from host scoping unit and makes it accessible here
+         implicit none
+         class(TFigure) :: this
+         real(rdp) :: calculate_area
+      end function calculate_area
+   end interface

Task/Abstract-type/NetRexx/abstract-type.netrexx

@@ -1,5 +1,5 @@
 /* NetRexx */
-options replace format comments java crossref savelog symbols binary
+options replace format comments java crossref symbols binary
 
 -- -----------------------------------------------------------------------------
 class RCAbstractType public final