Add support for operators to custom type

This is done by implementing the required functions for your custom type.

Sadly I could not solve this by using the regular traits like `Add`,
since I can't easily check if a different trait is implemented.

src/main.rs

@@ -1,4 +1,7 @@
-use std::{any::Any, fs::read_to_string};
+use std::{
+    any::Any,
+    fs::read_to_string,
+};
 
 use env::Env;
 use function::FunctionMap;
@@ -55,6 +58,14 @@ impl CustomValue for Foo {
         map.insert_native("edit_foo", Foo::edit);
         Some(map)
     }
+
+    fn add(&self, other: &Value) -> Value {
+        if let Some(v) = other.as_t::<Foo>() {
+            Foo { x: self.x + v.x }.into()
+        } else {
+            Value::default()
+        }
+    }
 }
 
 fn main() {
@@ -67,6 +78,7 @@ fn main() {
     });
     m.insert_native("waluigi", || "Waluigi");
     m.insert_native("native_test", || Foo { x: 41 });
+    m.insert_native("other_foo", || Foo { x: 1 });
 
     run(&m, &res);
 }

src/value/custom.rs

@@ -34,6 +34,27 @@ pub trait CustomValue: std::fmt::Debug + BoxClone {
     fn to_bool(&self) -> bool {
         true
     }
+
+    fn add(&self, _: &Value) -> Value {
+        Value::default()
+    }
+
+    fn sub(&self, _: &Value) -> Value {
+        Value::default()
+    }
+
+    fn mul(&self, _: &Value) -> Value {
+        Value::default()
+    }
+
+    fn div(&self, _: &Value) -> Value {
+        Value::default()
+    }
+
+    fn rem(&self, _: &Value) -> Value {
+        Value::default()
+    }
+
 }
 
 impl PartialEq<Value> for dyn CustomValue {

src/value/mod.rs

@@ -125,6 +125,9 @@ macro_rules! math_trait {
                 match (self, other) {
                     (Value::Int(lhs), Value::Int(rhs)) => Value::Int(lhs.$function_name(rhs)),
                     (Value::Float(lhs), Value::Float(rhs)) => Value::Float(lhs.$function_name(rhs)),
+                    (Value::Custom(lhs), rhs) => {
+                        lhs.$function_name(&rhs)
+                    }
                     _ => Value::Error,
                 }
             }

test.foo

@@ -32,4 +32,11 @@ if x == 0 {
 print(x);
 
 let x = 5;
-print(if x < 10 { 20 } else { 30 });
+print(if x < 10 { 20 } else { 30 });
+
+let f1 = native_test();
+let f2 = other_foo();
+
+let f3 = f1 + f2;
+
+print(f3);