fix: flawed function parsing

enumerating after filtering made the index unusable

src/nodes/evaluate.rs

@@ -31,12 +31,11 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
 
     while let Some((index, variant)) = nodes[start..end]
         .iter()
-        .filter_map(|n| match n {
+        .enumerate()
-            Node::Function(f) => Some(f),
+        .filter_map(|(i, n)| match n {
+            Node::Function(f) => Some((i, *f)),
             _ => None,
         })
-        .cloned()
-        .enumerate()
         .next()
     {
         match &mut nodes[start..end][index + 1] {
@@ -50,7 +49,7 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
                 Function::Secant => n.sec_mut(),
                 Function::CoSecant => n.csc_mut(),
             },
-            _ => panic!("function is missing an argument"),
+            n => panic!("function is missing an argument, got: {n:?}"),
         };
 
         nodes.remove(start + index);

src/nodes/mod.rs

@@ -11,7 +11,7 @@ mod tests;
 
 pub const PREC: u32 = 512;
 
-#[derive(Default, Debug, Clone, PartialEq)]
+#[derive(Debug, Default, Clone, PartialEq)]
 pub struct Nodes(Vec<Node>);
 impl AsRef<[Node]> for Nodes {
     fn as_ref(&self) -> &[Node] {
@@ -19,7 +19,7 @@ impl AsRef<[Node]> for Nodes {
     }
 }
 
-#[derive(Clone, Debug, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 enum Node {
     Function(Function),
     ParenthesisStart,
@@ -28,7 +28,7 @@ enum Node {
     Operator(Operator),
 }
 
-#[derive(Default, Clone, Debug, PartialEq)]
+#[derive(Debug, Default, Copy, Clone, PartialEq)]
 enum Operator {
     Plus,
     Minus,
@@ -38,7 +38,7 @@ enum Operator {
     Exp,
 }
 
-#[derive(Clone, Debug, PartialEq)]
+#[derive(Debug, Copy, Clone, PartialEq)]
 enum Function {
     Sine,
     ArcSine,