gistfile1.txt

/// Executes a list of expressions.
pub fn exec<Env>(mut a: ~[Expr<(), Env>]) -> Expr<(), Env> {
	Expr {
		run: proc(env: &mut Env) {
			for i in range(0, a.len()) {
				let (_, exn) = (a[i].run)(env);
				a[i] = exn;
			}
			((), exec(a))
		}
	}
}

COMPILER ERROR:

error: cannot assign to immutable vec content
/home/sven/Desktop/prob/src/expr/lib.rs:125 				a[i] = exn;