Add module trait

src/main.rs

@@ -2,9 +2,11 @@
 
 use cli::Config;
 use runtime::Runtime;
+use module::Module;
 
 mod cli;
 mod runtime;
+mod module;
 
 fn main() {
     let mut config = Config::new();

src/module.rs

@@ -0,0 +1,49 @@
+use runtime::Runtime;
+
+pub struct ModuleError {
+    shortdesc : String,
+    longdesc  : String,
+}
+
+impl ModuleError {
+
+    pub fn short(short : String) -> ModuleError {
+        ModuleError::new(short, "".to_string())
+    }
+
+    pub fn new(short : String, long : String) -> ModuleError {
+        ModuleError {
+            shortdesc: short,
+            longdesc: long,
+        }
+    }
+
+    pub fn print(&self, rt : &Runtime) {
+        if self.longdesc.is_empty() {
+            let s = format!("Error: {}\n\n{}\n\n",
+                            self.shortdesc, self.longdesc);
+            rt.print(&s)
+        } else {
+            let s = format!("Error: {}\n", self.shortdesc);
+            rt.print(&s)
+        }
+    }
+
+    pub fn print_short(&self, rt : &Runtime) {
+        rt.print(&self.shortdesc)
+    }
+
+    pub fn print_long(&self, rt : &Runtime) {
+        rt.print(&self.longdesc)
+    }
+
+}
+
+pub trait Module {
+
+    fn load(self, &rt : Runtime) -> Self;
+    fn name(self) -> String;
+
+    fn execute(self, &rt : Runtime) -> Option<ModuleError>;
+
+}