fix: constant implicit mult

before, "pi 2" caused a panic while "2 pi" worked just fine.
now both directions work :)

src/nodes/parse.rs

@@ -126,6 +126,12 @@ impl FromStr for Nodes {
                         && !(c == 'e' && filtered_string.chars().nth(i + 1).is_some_and(|c| c == '-'))
                         && !(c == '-' && filtered_string.chars().nth(i - 1).is_some_and(|c| c == 'e'))
                     {
+                        // likely a constant before this number
+                        // no need to check for parenthesis though (why?)
+                        if matches!(nodes.last(), Some(Node::Number(_))) {
+                            nodes.push(Node::Operator(Default::default()));
+                        }
+
                         nodes.push(Node::from(
                             Float::parse(&filtered_string[start_index..i]).map_err(|e| {
                                 Error::NumberParsing(filtered_string[start_index..i].to_owned(), e)
@@ -180,7 +186,7 @@ impl FromStr for Nodes {
                 );
             }
             ParsingState::ReadingNumber(start_index) => {
-                if matches!(nodes.last(), Some(Node::ParenthesisEnd)) {
+                if matches!(nodes.last(), Some(Node::ParenthesisEnd | Node::Number(_))) {
                     nodes.push(Node::Operator(Default::default()));
                 }
                 nodes.push(Node::from(

src/nodes/tests.rs

@@ -38,3 +38,9 @@ fn unary_operators() {
     assert_eq!(eval("-10"), -10.);
     assert_eq!(eval("+10"), 10.);
 }
+
+#[test]
+fn constant_implicit_mult() {
+    assert_eq!(eval("2pi"), 6.283185307179586);
+    assert_eq!(eval("pi2"), 6.283185307179586);
+}