From 0ab73e47af2bba3fb2ff6a4bf08ada4a3309bf3e Mon Sep 17 00:00:00 2001
From: Arnaud Bailly <arnaud.bailly@iohk.io>
Date: Sat, 12 Oct 2024 10:07:07 +0200
Subject: Add java evaluator

---
 java/LCEvaluator.java | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 java/LCEvaluator.java

(limited to 'java/LCEvaluator.java')

diff --git a/java/LCEvaluator.java b/java/LCEvaluator.java
new file mode 100644
index 0000000..b0fe69b
--- /dev/null
+++ b/java/LCEvaluator.java
@@ -0,0 +1,59 @@
+package org.lambdanantes.lcgoji;
+
+import org.lambdanantes.lcgoji.ast.Abs;
+import org.lambdanantes.lcgoji.ast.App;
+import org.lambdanantes.lcgoji.ast.Term;
+import org.lambdanantes.lcgoji.ast.Var;
+
+import static org.lambdanantes.lcgoji.ast.Abs.λ;
+import static org.lambdanantes.lcgoji.ast.App.apply;
+
+public class LCEvaluator {
+
+    public static Term evaluate(Term term) {
+        switch (term) {
+            case Var var -> {
+                return var;
+            }
+            case Abs abs -> {
+                return abs;
+            }
+            case App app -> {
+                switch (app.left) {
+                    case Abs abs -> {
+                        return substitute(abs.body, abs.arg, app.right);
+                    }
+                    case App _app -> {
+                        return app;
+                    }
+                    case Var _var -> {
+                        return app;
+                    }
+                }
+            }
+        }
+    }
+
+    private static Term substitute(Term body, String arg, Term val) {
+        switch (body) {
+            case Var var -> {
+                if (var.name.equals(arg)) {
+                    return val;
+                } else {
+                    return body;
+                }
+            }
+            case App app -> {
+                return apply(substitute(app.left, arg, val), substitute(app.right, arg, val));
+            }
+            case Abs abs -> {
+                if (abs.arg.equals(arg)) {
+                    // Pas de substitution des variables redéfinies
+                    return abs;
+                } else {
+                    return λ(abs.arg, substitute(abs.body, arg, val));
+                }
+            }
+        }
+    }
+}
\ No newline at end of file
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