ram@zedat.fu-berlin.de (Stefan Ram) wrote or quoted:
ifTrue: aBlock
^aBlock value
>
and "False" with
>
ifTrue: aBlock
^nil
Heads up: All code of this post was generated and not tested!
Here's an extended program, supossed to run unter GNU Smalltalk:
Object subclass: Boolean [
Boolean class >> new [
self error: 'Boolean instances cannot be created'
]
ifTrue: trueBlock [
self subclassResponsibility
]
ifFalse: falseBlock [
self subclassResponsibility
]
ifTrue: trueBlock ifFalse: falseBlock [
self subclassResponsibility
]
]
Boolean subclass: True [
ifTrue: trueBlock [
^trueBlock value
]
ifFalse: falseBlock [
^nil
]
ifTrue: trueBlock ifFalse: falseBlock [
^trueBlock value
]
]
Boolean subclass: False [
ifTrue: trueBlock [
^nil
]
ifFalse: falseBlock [
^falseBlock value
]
ifTrue: trueBlock ifFalse: falseBlock [
^falseBlock value
]
]
"Create global instances"
true := True new.
false := False new.
"Example usage"
a := -5.
a < 0 ifTrue: [a := 0].
a printNl.
b := 10.
b < 0 ifTrue: [b := 0].
b printNl.
(a = 0 and: [b = 10]) ifTrue: [
'Both conditions are true' printNl
] ifFalse: [
'At least one condition is false' printNl
].
, expected output:
0
10
Both conditions are true
, Common Lisp,
;; Define the Boolean class (in Common Lisp, we'll use structures)
(defstruct (boolean (:constructor nil)))
;; Define True and False subclasses
(defstruct (true (:include boolean)))
(defstruct (false (:include boolean)))
;; Create global instances
(defparameter *true* (make-true))
(defparameter *false* (make-false))
;; Define methods for True
(defmethod if-true ((condition true) true-block)
(funcall true-block))
(defmethod if-false ((condition true) false-block)
nil)
(defmethod if-true-false ((condition true) true-block false-block)
(funcall true-block))
;; Define methods for False
(defmethod if-true ((condition false) true-block)
nil)
(defmethod if-false ((condition false) false-block)
(funcall false-block))
(defmethod if-true-false ((condition false) true-block false-block)
(funcall false-block))
;; Helper function to convert boolean to our custom boolean objects
(defun to-boolean (value)
(if value *true* *false*))
;; Example usage
(let ((a -5))
(if-true (to-boolean (< a 0))
(lambda () (setf a 0)))
(print a))
(let ((b 10))
(if-true (to-boolean (< b 0))
(lambda () (setf b 0)))
(print b))
(if-true-false (to-boolean (and (= a 0) (= b 10)))
(lambda () (print "Both conditions are true"))
(lambda () (print "At least one condition is false")))
, Python,
from abc import ABC, abstractmethod
class Boolean(ABC):
@abstractmethod
def if_true(self, block):
pass
@abstractmethod
def if_false(self, block):
pass
@abstractmethod
def if_true_if_false(self, true_block, false_block):
pass
class True(Boolean):
def if_true(self, block):
return block()
def if_false(self, block):
return None
def if_true_if_false(self, true_block, false_block):
return true_block()
class False(Boolean):
def if_true(self, block):
return None
def if_false(self, block):
return block()
def if_true_if_false(self, true_block, false_block):
return false_block()
# Create global instances
true = True()
false = False()
# Example usage
a = -5
(true if a < 0 else false).if_true(lambda: globals().update(a=0))
print(a)
b = 10
(true if b < 0 else false).if_true(lambda: globals().update(b=0))
print(b)
(true if a == 0 and b == 10 else false).if_true_if_false(
lambda: print("Both conditions are true"),
lambda: print("At least one condition is false")
)
, Java,
import java.util.function.Supplier;
abstract class Boolean {
abstract <T> T ifTrue(Supplier<T> trueBlock);
abstract <T> T ifFalse(Supplier<T> falseBlock);
abstract <T> T ifTrueIfFalse(Supplier<T> trueBlock, Supplier<T> falseBlock);
}
class True extends Boolean {
@Override
<T> T ifTrue(Supplier<T> trueBlock) {
return trueBlock.get();
}
@Override
<T> T ifFalse(Supplier<T> falseBlock) {
return null;
}
@Override
<T> T ifTrueIfFalse(Supplier<T> trueBlock, Supplier<T> falseBlock) {
return trueBlock.get();
}
}
class False extends Boolean {
@Override
<T> T ifTrue(Supplier<T> trueBlock) {
return null;
}
@Override
<T> T ifFalse(Supplier<T> falseBlock) {
return falseBlock.get();
}
@Override
<T> T ifTrueIfFalse(Supplier<T> trueBlock, Supplier<T> falseBlock) {
return falseBlock.get();
}
}
public class SmalltalkToJava {
private static final Boolean TRUE = new True();
private static final Boolean FALSE = new False();
public static void main(String[] args) {
int[] a = {-5};
(a[0] < 0 ? TRUE : FALSE).ifTrue(() -> {
a[0] = 0;
return null;
});
System.out.println(a[0]);
int[] b = {10};
(b[0] < 0 ? TRUE : FALSE).ifTrue(() -> {
b[0] = 0;
return null;
});
System.out.println(b[0]);
(a[0] == 0 && b[0] == 10 ? TRUE : FALSE).ifTrueIfFalse(
() -> {
System.out.println("Both conditions are true");
return null;
},
() -> {
System.out.println("At least one condition is false");
return null;
}
);
}
}
, C++,
#include <iostream>
#include <functional>
class Boolean {
public:
virtual void ifTrue(const std::function<void()>& block) = 0;
virtual void ifFalse(const std::function<void()>& block) = 0;
virtual void ifTrue(const std::function<void()>& trueBlock, const std::function<void()>& falseBlock) = 0;
};
class True : public Boolean {
public:
void ifTrue(const std::function<void()>& block) override {
block();
}
void ifFalse(const std::function<void()>& block) override {}
void ifTrue(const std::function<void()>& trueBlock, const std::function<void()>& falseBlock) override {
trueBlock();
}
};
class False : public Boolean {
public:
void ifTrue(const std::function<void()>& block) override {}
void ifFalse(const std::function<void()>& block) override {
block();
}
void ifTrue(const std::function<void()>& trueBlock, const std::function<void()>& falseBlock) override {
falseBlock();
}
};
int main() {
True true_obj;
False false_obj;
int a = -5;
(a < 0 ? true_obj : false_obj).ifTrue([&]() { a = 0; });
std::cout << a << std::endl;
int b = 10;
(b < 0 ? true_obj : false_obj).ifTrue([&]() { b = 0; });
std::cout << b << std::endl;
(a == 0 && b == 10 ? true_obj : false_obj).ifTrue(
[]() { std::cout << "Both conditions are true" << std::endl; },
[]() { std::cout << "At least one condition is false" << std::endl; }
);
return 0;
}
, C,
#include <stdio.h>
#include <stdbool.h>
typedef struct Boolean Boolean;
typedef struct True True;
typedef struct False False;
struct Boolean {
void (*ifTrue)(Boolean* self, void (*block)(void));
void (*ifFalse)(Boolean* self, void (*block)(void));
void (*ifTrueIfFalse)(Boolean* self, void (*trueBlock)(void), void (*falseBlock)(void));
};
struct True {
Boolean base;
};
struct False {
Boolean base;
};
void True_ifTrue(Boolean* self, void (*block)(void)) {
block();
}
void True_ifFalse(Boolean* self, void (*block)(void)) {
// Do nothing
}
void True_ifTrueIfFalse(Boolean* self, void (*trueBlock)(void), void (*falseBlock)(void)) {
trueBlock();
}
void False_ifTrue(Boolean* self, void (*block)(void)) {
// Do nothing
}
void False_ifFalse(Boolean* self, void (*block)(void)) {
block();
}
void False_ifTrueIfFalse(Boolean* self, void (*trueBlock)(void), void (*falseBlock)(void)) {
falseBlock();
}
True true_obj = {{True_ifTrue, True_ifFalse, True_ifTrueIfFalse}};
False false_obj = {{False_ifTrue, False_ifFalse, False_ifTrueIfFalse}};
#define TRUE ((Boolean*)&true_obj)
#define FALSE ((Boolean*)&false_obj)
int main() {
int a = -5;
(a < 0 ? TRUE : FALSE)->ifTrue(^{
a = 0;
});
printf("%d\n", a);
int b = 10;
(b < 0 ? TRUE : FALSE)->ifTrue(^{
b = 0;
});
printf("%d\n", b);
(a == 0 && b == 10 ? TRUE : FALSE)->ifTrueIfFalse(
^{ printf("Both conditions are true\n"); },
^{ printf("At least one condition is false\n"); }
);
return 0;
}
.
Alan Kay on OOP
Re: Alan Kay on OOP
