Add Lambda Calculus in Java

languages/j/java/LambdaCore.java

@@ -0,0 +1,65 @@
+import java.util.function.Function;
+
+public interface LambdaCore {
+
+    interface Bool extends Function<Bool, Function<Bool, Bool>> {
+    }
+
+    interface UnaryBoolOp extends Function<Bool, Bool> {
+    }
+
+    interface BinaryBoolOp extends Function<Bool, Function<Bool, Bool>> {
+    }
+
+    interface ChurchNumeral extends Function<Function<Integer, Integer>, Function<Integer, Integer>> {
+    }
+
+    Bool TRUE = x -> y -> x;
+    Bool FALSE = x -> y -> y;
+
+    UnaryBoolOp NOT = b -> b.apply(FALSE).apply(TRUE);
+    BinaryBoolOp AND = b1 -> b2 -> b1.apply(b2).apply(FALSE);
+    BinaryBoolOp OR = b1 -> b2 -> b1.apply(TRUE).apply(b2);
+
+    ChurchNumeral ZERO = x -> y -> y;
+    Function<ChurchNumeral, ChurchNumeral> SUCC = w -> y -> x -> y.apply(w.apply(y).apply(x));
+
+//    Function<ChurchNumeral, ChurchNumeral> PRED = n -> f -> x ->
+//            n.apply(g -> h -> h.apply(g.apply(f)))
+//                    .apply(u -> x)
+//                    .apply(u -> u);
+
+    static void main(String[] args) {
+        printBool(TRUE);                                // TRUE
+        printBool(FALSE);                               // FALSE
+
+        printBool(NOT.apply(TRUE));                     // FALSE
+        printBool(NOT.apply(FALSE));                    // TRUE
+
+        printBool(AND.apply(FALSE).apply(FALSE));       // FALSE
+        printBool(AND.apply(TRUE).apply(FALSE));        // FALSE
+        printBool(AND.apply(FALSE).apply(TRUE));        // FALSE
+        printBool(AND.apply(TRUE).apply(TRUE));         // TRUE
+
+        printBool(OR.apply(FALSE).apply(FALSE));        // FALSE
+        printBool(OR.apply(TRUE).apply(FALSE));         // TRUE
+        printBool(OR.apply(FALSE).apply(TRUE));         // TRUE
+        printBool(OR.apply(TRUE).apply(TRUE));          // TRUE
+
+        printChurchNumeral(ZERO);                       // 0
+        printChurchNumeral(SUCC.apply(ZERO));           // 1
+    }
+
+    static void printBool(Bool b) {
+        if (b == TRUE)
+            System.out.println("BOOLEAN TRUE");
+        else if (b == FALSE)
+            System.out.println("BOOLEAN FALSE");
+        else
+            throw new IllegalStateException();
+    }
+
+    static void printChurchNumeral(ChurchNumeral n) {
+        System.out.println(n.apply(x -> x + 1).apply(0));
+    }
+}

languages/j/java/README.md

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+# Java 21 Installation Guide
+
+## Download Java 21
+Download Java 21 from the official Oracle website:
+[Java 21 Downloads](https://www.oracle.com/in/java/technologies/downloads/#java21)
+
+## Installation Steps
+1. Select the appropriate JDK version for your OS (Windows, macOS, or Linux).
+2. Download the installer or compressed archive.
+3. Follow the installation instructions provided by Oracle.
+
+## Verify Installation
+Run the following command to check the installed Java version:
+
+```sh
+java -version
+```
+
+# Run Code
+
+```sh
+java LambdaCore.java
+```