From 9c77fa8aeb10420a9997e63c11377327cd93ce57 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Fri, 1 Sep 2017 18:23:44 -0700
Subject: [PATCH] Add a DomainException that avoids using null in functions.

---
 .../nwapw/abacus/number/DomainException.java  | 24 +++++++++++++++++++
 .../abacus/function/applicable/Applicable.kt  |  7 +++---
 .../function/applicable/ReducerApplicable.kt  |  7 +++---
 .../org/nwapw/abacus/fx/AbacusController.java |  2 ++
 4 files changed, 34 insertions(+), 6 deletions(-)
 create mode 100644 core/src/main/java/org/nwapw/abacus/number/DomainException.java

diff --git a/core/src/main/java/org/nwapw/abacus/number/DomainException.java b/core/src/main/java/org/nwapw/abacus/number/DomainException.java
new file mode 100644
index 0000000..51a1769
--- /dev/null
+++ b/core/src/main/java/org/nwapw/abacus/number/DomainException.java
@@ -0,0 +1,24 @@
+package org.nwapw.abacus.number;
+
+/**
+ * Exception thrown if the function parameters do not match
+ * requirements.
+ */
+public class DomainException extends RuntimeException {
+
+    /**
+     * Creates a new DomainException.
+     * @param reason the reason for which the exception is thrown.
+     */
+    public DomainException(String reason) {
+        super(reason);
+    }
+
+    /**
+     * Creates a new DomainException with a default message.
+     */
+    public DomainException(){
+        this("Domain Error");
+    }
+
+}
diff --git a/core/src/main/kotlin/org/nwapw/abacus/function/applicable/Applicable.kt b/core/src/main/kotlin/org/nwapw/abacus/function/applicable/Applicable.kt
index 69f0afc..dce1129 100644
--- a/core/src/main/kotlin/org/nwapw/abacus/function/applicable/Applicable.kt
+++ b/core/src/main/kotlin/org/nwapw/abacus/function/applicable/Applicable.kt
@@ -1,5 +1,6 @@
 package org.nwapw.abacus.function.applicable
 
+import org.nwapw.abacus.number.DomainException
 import org.nwapw.abacus.plugin.NumberImplementation
 
 /**
@@ -25,7 +26,7 @@ interface Applicable<in T : Any, out O : Any> {
      * @param params the parameters to apply to.
      * @return the result of the application.
      */
-    fun applyInternal(implementation: NumberImplementation, params: Array<out T>): O?
+    fun applyInternal(implementation: NumberImplementation, params: Array<out T>): O
 
     /**
      * If the parameters can be used with this applicable, returns
@@ -34,8 +35,8 @@ interface Applicable<in T : Any, out O : Any> {
      * @param params the parameters to apply to.
      * @return the result of the operation, or null if parameters do not match.
      */
-    fun apply(implementation: NumberImplementation, vararg params: T): O? {
-        if (!matchesParams(implementation, params)) return null
+    fun apply(implementation: NumberImplementation, vararg params: T): O {
+        if (!matchesParams(implementation, params)) throw DomainException()
         return applyInternal(implementation, params)
     }
 
diff --git a/core/src/main/kotlin/org/nwapw/abacus/function/applicable/ReducerApplicable.kt b/core/src/main/kotlin/org/nwapw/abacus/function/applicable/ReducerApplicable.kt
index bdb3276..9a80edc 100644
--- a/core/src/main/kotlin/org/nwapw/abacus/function/applicable/ReducerApplicable.kt
+++ b/core/src/main/kotlin/org/nwapw/abacus/function/applicable/ReducerApplicable.kt
@@ -1,5 +1,6 @@
 package org.nwapw.abacus.function.applicable
 
+import org.nwapw.abacus.number.DomainException
 import org.nwapw.abacus.plugin.NumberImplementation
 import org.nwapw.abacus.tree.Reducer
 
@@ -27,7 +28,7 @@ interface ReducerApplicable<in T : Any, out O : Any, in R : Any> {
      * @param params the arguments to apply to.
      * @return the result of the application.
      */
-    fun applyWithReducerInternal(implementation: NumberImplementation, reducer: Reducer<R>, params: Array<out T>): O?
+    fun applyWithReducerInternal(implementation: NumberImplementation, reducer: Reducer<R>, params: Array<out T>): O
 
     /**
      * Applies this applicable to the given arguments, and reducer,
@@ -36,8 +37,8 @@ interface ReducerApplicable<in T : Any, out O : Any, in R : Any> {
      * @param params the arguments to apply to.
      * @return the result of the application, or null if the arguments are incompatible.
      */
-    fun applyWithReducer(implementation: NumberImplementation, reducer: Reducer<R>, vararg params: T): O? {
-        if (!matchesParams(implementation, params)) return null
+    fun applyWithReducer(implementation: NumberImplementation, reducer: Reducer<R>, vararg params: T): O {
+        if (!matchesParams(implementation, params)) throw DomainException()
         return applyWithReducerInternal(implementation, reducer, params)
     }
 
diff --git a/fx/src/main/java/org/nwapw/abacus/fx/AbacusController.java b/fx/src/main/java/org/nwapw/abacus/fx/AbacusController.java
index 4f62247..45cdf76 100644
--- a/fx/src/main/java/org/nwapw/abacus/fx/AbacusController.java
+++ b/fx/src/main/java/org/nwapw/abacus/fx/AbacusController.java
@@ -152,6 +152,8 @@ public class AbacusController implements PluginListener {
                 return resultingString;
             } catch (ComputationInterruptedException exception) {
                 return ERR_STOP;
+            } catch (DomainException exception) {
+                return exception.getMessage();
             } catch (RuntimeException exception) {
                 exception.printStackTrace();
                 return ERR_EXCEPTION;