refactor: Herstructurering

src/prolog/ast/terms/Variable.kt

@@ -0,0 +1,38 @@
+package prolog.ast.terms
+
+import java.util.*
+
+data class Variable(val name: String) : Term {
+    private var alias: Optional<Term> = Optional.empty()
+
+    fun alias(): Optional<Term> {
+        return alias
+    }
+
+    fun bind(term: Term): Optional<Term> {
+        if (alias.isEmpty) {
+            alias = Optional.of(term)
+        }
+
+        return alias
+    }
+
+    fun unbind() {
+        alias = Optional.empty()
+    }
+
+    override fun compareTo(other: Term): Int {
+        return when (other) {
+            is Variable -> name.compareTo(other.name)
+            // Variables are always less than atoms
+            else -> -1
+        }
+    }
+
+    override fun toString(): String {
+        return when {
+            alias.isPresent -> "$name: ${alias.get()}"
+            else -> name
+        }
+    }
+}