Fix #7 panic on too few function arguments

Signed-off-by: trivernis <trivernis@protonmail.com>

src/elements/mod.rs

@@ -15,6 +15,7 @@ pub enum Element {
     Special(Special),
     Group(Group),
     Accent(ExpressionAccent),
+    Null,
 }
 
 impl Boxed for Element {}

src/format/mathml.rs

@@ -696,6 +696,7 @@ impl ToMathML for Element {
             Element::Literal(l) => l.to_mathml(),
             Element::Group(g) => g.to_mathml(),
             Element::Accent(a) => a.to_mathml(),
+            Element::Null => "".to_string(),
         }
     }
 }

src/parsing/tree_parser.rs

@@ -228,21 +228,21 @@ impl TreeParser {
             Misc::LatexFrac => {
                 self.step();
                 Element::Special(Special::Frac(Frac {
-                    top: self.parse_element().unwrap().boxed(),
-                    bottom: self.parse_element().unwrap().boxed(),
+                    top: self.parse_element().unwrap_or(Element::Null).boxed(),
+                    bottom: self.parse_element().unwrap_or(Element::Null).boxed(),
                 }))
             }
             Misc::Sqrt => {
                 self.step();
                 Element::Special(Special::Sqrt(Sqrt {
-                    inner: self.parse_element().unwrap().boxed(),
+                    inner: self.parse_element().unwrap_or(Element::Null).boxed(),
                 }))
             }
             Misc::Root => {
                 self.step();
-                let base = self.parse_element().unwrap().boxed();
+                let base = self.parse_element().unwrap_or(Element::Null).boxed();
                 self.step();
-                let inner = self.parse_element().unwrap().boxed();
+                let inner = self.parse_element().unwrap_or(Element::Null).boxed();
                 Element::Special(Special::Root(Root { inner, base }))
             }
             Misc::Int => Element::Special(Special::Integral(Integral {
@@ -432,7 +432,11 @@ impl TreeParser {
             self.step();
             Some(Pow {
                 base: previous.clone().boxed(),
-                exp: self.parse_element().unwrap().to_non_enclosed().boxed(),
+                exp: self
+                    .parse_element()
+                    .unwrap_or(Element::Null)
+                    .to_non_enclosed()
+                    .boxed(),
             })
         } else {
             None
@@ -446,7 +450,11 @@ impl TreeParser {
             self.step();
             Some(Sub {
                 base: previous.clone().boxed(),
-                lower: self.parse_element().unwrap().to_non_enclosed().boxed(),
+                lower: self
+                    .parse_element()
+                    .unwrap_or(Element::Null)
+                    .to_non_enclosed()
+                    .boxed(),
             })
         } else {
             None

src/tests/parsing.rs

@@ -228,5 +228,23 @@ fn it_parses_roots() {
                 .boxed(),
             }))]
         }
+    );
+    // test no fail
+    parse("root 3".to_string());
+}
+
+#[test]
+fn it_parses_functions() {
+    let expr = parse("sin 10".to_string());
+    assert_eq!(
+        expr,
+        Expression {
+            children: vec![
+                Element::Literal(Literal::Function(Function::Sin)),
+                Element::Literal(Literal::Number(Number {
+                    number: "10".to_string()
+                }))
+            ]
+        }
     )
 }