Fully fledged lambdas, along with efficiency tweaks across the ast

src/stl/boolean.rs

@@ -127,7 +127,6 @@ Integers and Floats will cast to true if they are 0 and false otherwise.";
 pub fn boolcast_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
     match &*ast.car {
         Ctr::Bool(_) => Ok(*ast.car.clone()),
-        Ctr::Symbol(_) => Err("not clear how to cast a symbol to a bool".to_string()),
         Ctr::String(s) => {
             if s == "true" {
                 Ok(Ctr::Bool(true))
@@ -139,7 +138,7 @@ pub fn boolcast_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String>
         },
         Ctr::Integer(i) => Ok(Ctr::Bool(*i == 0)),
         Ctr::Float(f) => Ok(Ctr::Bool(*f == 0.0)),
-        Ctr::Seg(_) => Err("cannot convert list to a boolean".to_string()),
-        Ctr::None => Err("Impossible task: cannot convert none to bool".to_string()),
+        _ => Err(format!("cannot convert a {} to a boolean",
+                         ast.car.to_type())),
     }
 }