Think I've nearly gotten it traitified correctly...

src/language.rs

@@ -18,13 +18,14 @@ pub struct ParseError {
 
 pub struct LLVMCodeString(pub String);
 
-pub trait ProgrammingLanguage<E: EvaluationMachine> {
+pub trait ProgrammingLanguage {
     type Token: Debug;
     type AST: Debug;
+    type Evaluator: EvaluationMachine;
 
     fn tokenize(input: &str) -> Result<Vec<Self::Token>, TokenError>;
     fn parse(input: Vec<Self::Token>) -> Result<Self::AST, ParseError>;
-    fn evaluate(ast: Self::AST, evaluator: &mut E) -> Vec<String>;
+    fn evaluate(ast: Self::AST, evaluator: &mut Self::Evaluator) -> Vec<String>;
     fn compile(ast: Self::AST) -> LLVMCodeString;
 }
 
@@ -32,3 +33,10 @@ pub trait EvaluationMachine {
     fn set_option(&mut self, option: &str, value: bool) -> bool;
     fn new() -> Self;
 }
+
+pub trait LanguageWrapper {
+}
+
+impl<X, T, A, E> LanguageWrapper for X where X: ProgrammingLanguage<Token=T, AST=A, Evaluator=E>, T: Debug, A: Debug, E: EvaluationMachine {
+
+}

src/maaru_lang/mod.rs

@@ -14,9 +14,10 @@ pub struct Token { }
 #[derive(Debug)]
 pub struct AST { }
 
-impl ProgrammingLanguage<MaaruEvaluator> for Maaru {
+impl ProgrammingLanguage for Maaru {
     type Token = Token;
     type AST = AST;
+    type Evaluator = MaaruEvaluator;
 
     fn tokenize(input: &str) -> Result<Vec<Self::Token>, TokenError> {
         Ok(vec![Token { }])
@@ -25,7 +26,7 @@ impl ProgrammingLanguage<MaaruEvaluator> for Maaru {
     fn parse(input: Vec<Self::Token>) -> Result<Self::AST, ParseError> {
         Ok(AST { })
     }
-    fn evaluate(ast: Self::AST, evaluator: &mut MaaruEvaluator) -> Vec<String> {
+    fn evaluate(ast: Self::AST, evaluator: &mut Self::Evaluator) -> Vec<String> {
         vec!["Unimplemented".to_string()]
     }
     fn compile(ast: Self::AST) -> LLVMCodeString {

src/main.rs

@@ -15,7 +15,7 @@ use schala_lang::Schala;
 mod maaru_lang;
 
 mod language;
-use language::{ProgrammingLanguage, LLVMCodeString, EvaluationMachine};
+use language::{ProgrammingLanguage, LanguageWrapper, LLVMCodeString, EvaluationMachine};
 
 mod llvm_wrap;
 
@@ -36,7 +36,7 @@ fn main() {
             repl.run();
         }
         [_, ref filename, _..] => {
-            let language = Schala { };
+            let language = Schala::new();
             run_noninteractive(filename, !option_matches.opt_present("i"), trace, &language);
         }
     };
@@ -56,7 +56,7 @@ fn program_options() -> getopts::Options {
     options
 }
 
-fn run_noninteractive<'a, T: ProgrammingLanguage<SchalaEvaluator<'a>>>(filename: &str, compile: bool, trace_evaluation: bool, language: &T) {
+fn run_noninteractive<'a, T: ProgrammingLanguage>(filename: &str, compile: bool, trace_evaluation: bool, language: &T) {
     let mut source_file = File::open(&Path::new(filename)).unwrap();
     let mut buffer = String::new();
     source_file.read_to_string(&mut buffer).unwrap();
@@ -81,7 +81,7 @@ fn run_noninteractive<'a, T: ProgrammingLanguage<SchalaEvaluator<'a>>>(filename:
     if compile {
         compilation_sequence(T::compile(ast), filename);
     } else {
-        let mut evaluator = <SchalaEvaluator as EvaluationMachine>::new();
+        let mut evaluator = <T as ProgrammingLanguage>::Evaluator::new();
         if trace_evaluation {
             evaluator.set_option("trace_evaluation", true);
         }
@@ -97,6 +97,7 @@ struct Repl<'a> {
     show_tokens: bool,
     show_parse: bool,
     show_llvm_ir: bool,
+    languages: Vec<Box<LanguageWrapper>>,
     evaluator: SchalaEvaluator<'a>,
     interpreter_directive_sigil: char,
     reader: LineReader,
@@ -114,6 +115,7 @@ impl<'a> Repl<'a> {
             show_tokens: false,
             show_parse: false,
             show_llvm_ir: show_llvm,
+            languages: vec![Box::new(Schala::new())],
             evaluator: evaluator,
             interpreter_directive_sigil: '.',
             reader: reader,
@@ -145,11 +147,12 @@ impl<'a> Repl<'a> {
     }
 
     fn input_handler(&mut self, input: &str) -> String {
-        let schala = Schala { };
+        let schala = Schala::new();
-        self.input_handler_new(input, schala)
+        let mut evaluator = <SchalaEvaluator as EvaluationMachine>::new();
+        self.input_handler_new(input, schala, &mut evaluator)
     }
 
-    fn input_handler_new<T: ProgrammingLanguage<SchalaEvaluator<'a>>>(&mut self, input: &str, language: T) -> String {
+    fn input_handler_new<T: ProgrammingLanguage>(&mut self, input: &str, language: T, mut evaluator: &mut T::Evaluator) -> String {
         let mut output = String::new();
 
         let tokens = match T::tokenize(input) {
@@ -181,7 +184,7 @@ impl<'a> Repl<'a> {
             output.push_str(&s);
         } else {
             // for now only handle last output
-            let mut full_output: Vec<String> = T::evaluate(ast, &mut self.evaluator);
+            let mut full_output: Vec<String> = T::evaluate(ast, &mut evaluator);
             output.push_str(&full_output.pop().unwrap_or("".to_string()));
         }
         output

src/schala_lang/mod.rs

@@ -1,3 +1,4 @@
+use ::std::marker::PhantomData;
 pub mod tokenizer;
 pub mod parser;
 pub mod eval;
@@ -7,20 +8,25 @@ use language::{ProgrammingLanguage, EvaluationMachine, ParseError, TokenError, L
 
 pub use self::eval::Evaluator as SchalaEvaluator;
 
-pub struct Schala { }
+pub struct Schala<'a> { marker: PhantomData<&'a ()> }
+impl<'a> Schala<'a> {
+    pub fn new() -> Schala<'a> {
+        Schala { marker: PhantomData }
+    }
+}
 
-impl<'a> ProgrammingLanguage<eval::Evaluator<'a>> for Schala {
+impl<'a> ProgrammingLanguage for Schala<'a> {
     type Token = tokenizer::Token;
     type AST = parser::AST;
+    type Evaluator = SchalaEvaluator<'a>;
 
     fn tokenize(input: &str) -> Result<Vec<Self::Token>, TokenError> {
         tokenizer::tokenize(input)
     }
-
     fn parse(input: Vec<Self::Token>) -> Result<Self::AST, ParseError> {
         parser::parse(&input, &[]).map_err(|x| ParseError { msg: x.msg })
     }
-    fn evaluate(ast: Self::AST, evaluator: &mut eval::Evaluator) -> Vec<String> {
+    fn evaluate(ast: Self::AST, evaluator: &mut Self::Evaluator) -> Vec<String> {
         evaluator.run(ast)
     }
     fn compile(ast: Self::AST) -> LLVMCodeString {