diff --git a/src/eval.rs b/src/eval.rs
index 8284258..0e31a68 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -21,6 +21,10 @@ impl Funcmap {
         let map = HashMap::new();
         Funcmap { map: map }
     }
+
+    fn lookup_function(&self, name: String) -> Option<Function> {
+        self.map.get(&name).map(|x| x.clone())
+    }
 }
 
 pub struct Evaluator {
@@ -66,9 +70,6 @@ impl Evaluator {
         self.funcmap.map.insert(name, function);
     }
 
-    fn lookup_function(&mut self, name: String) -> Option<&Function> {
-        self.funcmap.map.get(&name)
-    }
 }
 
 trait Evaluable {
@@ -208,11 +209,27 @@ impl Evaluator {
 
     fn reduce_call(&mut self, name: String, arguments: Vec<Expression>) -> Expression {
         use parser::Expression::*;
-        let function = match self.lookup_function(name) {
-            Some(ref func) => func.clone(),
+        let x = self.funcmap.lookup_function(name);
+        let function = match x {
+            Some(func) => func,
             None => return Null
         };
 
+        if function.prototype.parameters.len() != arguments.len() {
+            return Null
+        }
+
+        let mut frame: Varmap = Varmap::new();
+        for (binding, expr) in function.prototype.parameters.iter().zip(arguments.iter()) {
+            frame.map.insert(binding.clone(), expr.clone());
+        }
+
+        self.frames.push(frame);
+        for expr in function.body.iter() {
+            self.reduce_expr(expr.clone());
+        }
+
+        self.frames.pop();
         Null
     }
 }
diff --git a/src/parser.rs b/src/parser.rs
index e9b8cbe..3fcec92 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -33,7 +33,7 @@ pub struct Function {
 #[derive(Debug, Clone, PartialEq)]
 pub struct Prototype {
     pub name: String,
-    pub args: Vec<String>
+    pub parameters: Vec<String>
 }
 
 #[derive(Debug, Clone)]
@@ -194,9 +194,9 @@ impl Parser {
         use tokenizer::Token::*;
         let name: String = expect_identifier!(self);
         expect!(self, LParen);
-        let args: Vec<String> = try!(self.identlist());
+        let parameters: Vec<String> = try!(self.identlist());
         expect!(self, RParen);
-        Ok(Prototype {name: name, args: args})
+        Ok(Prototype {name: name, parameters: parameters})
     }
 
     fn identlist(&mut self) -> ParseResult<Vec<String>> {