September Morn Update

Task/Abstract-type/C/abstract-type-2.c

@@ -1,6 +1,7 @@
 #ifndef SILLY_H
 #define SILLY_H
 #include "intefaceAbs.h"
+#include <stdlib.h>
 
 typedef struct sillyStruct *Silly;
 extern Silly NewSilly( double, const char *);

Task/Abstract-type/C/abstract-type-3.c

@@ -1,6 +1,5 @@
 #include "silly.h"
 #include <string.h>
-#include <stdlib.h>
 #include <stdio.h>
 
 struct sillyStruct {

Task/Abstract-type/Crystal/abstract-type.crystal

@@ -0,0 +1,40 @@
+abstract class Animal # only abstract class can have abstract methods
+  abstract def move
+  abstract def think
+
+  # abstract class can have normal fields and methods
+  def initialize(@name : String)
+  end
+
+  def process
+    think
+    move
+  end
+end
+
+# WalkingAnimal still have to be declared abstract because `think` was not implemented
+abstract class WalkingAnimal < Animal
+  def move
+    puts "#{@name} walks"
+  end
+end
+
+class Human < WalkingAnimal
+  property in_car = false
+
+  def move
+    if in_car
+      puts "#{@name} drives a car"
+    else
+      super
+    end
+  end
+
+  def think
+    puts "#{@name} thinks"
+  end
+end
+
+# Animal.new # => can't instantiate abstract class
+he = Human.new("Andrew") # ok
+he.process

Task/Abstract-type/Mercury/abstract-type.mercury

@@ -0,0 +1,26 @@
+:- module eq.
+:- interface.
+
+:- typeclass eq(T) where [
+    pred (T::in) == (T::in) is semidet,
+    pred (T::in) \= (T::in) is semidet
+].
+
+:- pred f(T::in) is semidet <= eq(T).
+
+:- type foo
+    --->    foo(
+                x :: int,
+                str :: string
+            ).
+
+:- instance eq(foo).
+
+:- implementation.
+
+f(X) :- X == X.
+
+:- instance eq(foo) where [
+    A == B :- (A^x = B^x, A^str = B^str),
+    A \= B :- not A == B
+].