fix(eval): early eval of arguments to functions

src/lisp/eval.rs

@@ -85,7 +85,7 @@ fn dispatch_anonymous_function(
     }
 
     for (arg, symbol) in args.iter_mut().zip(argument_symbols.iter()) {
-        overlay.set(symbol.to_owned(), arg.to_owned());
+        overlay.set(symbol.to_owned(), eval(env, arg.to_owned())?);
     }
 
     eval(&env.overlay(overlay), body)

src/lisp/prelude.rs

@@ -161,10 +161,11 @@ pub fn prelude_gt(env: &Environment, expr: Expression) -> Result<Expression, Eva
 pub fn prelude_set(env: &Environment, expr: Expression) -> Result<Expression, EvalError> {
     let [s, e] = expr.try_into()?;
 
-    match s {
+    match eval(env, s)? {
         Expression::Symbol(s) => {
-            env.shared_set(s, e);
-            Ok(Expression::Nil)
+            let e = eval(env, e)?;
+            env.shared_set(s, e.clone());
+            Ok(e)
         }
         x => Err(EvalError::NotASymbol(x)),
     }

src/main.rs

@@ -6,8 +6,8 @@ use crate::lisp::{eval, Environment};
 
 fn main() {
     let program1 = "((lambda (x y) (+ (if (< x 10) (* x 11) x) y)) 2 20)";
-    let program2 = "(set myvar \"hello world!\")";
-    let program3 = "(print myvar)";
+    let program2 = "(set 'myvar \"hello world!\")";
+    let program3 = "(print myvar) (print 'myvar)";
 
     let environment = Environment::default();