Use a macro to cut down on the if statement boilerplate

src/lib.rs

@@ -69,6 +69,19 @@ pub struct JSON {
     i: usize,
 }
 
+/// Cut down the if boilerplate
+///
+/// Thanks to `uwaterloodudette` on reddit
+macro_rules! try_parse {
+    ($( $e:expr ),* ) => {
+        $(
+            if let Some(v) = $e? {
+                return Ok(v);
+            }
+        )*
+    };
+}
+
 impl JSON {
     /// Private constructor
     fn new(json: &str) -> Self {
@@ -82,34 +95,22 @@ impl JSON {
     fn parse_value(&mut self) -> Result<JSONValue, ParseError> {
         self.skip_whitespace();
 
-        return if let Some(string) = self.parse_string()? {
-            Ok(string)
-        } else if let Some(number) = self.parse_number()? {
-            Ok(number)
-        } else if let Some(object) = self.parse_object()? {
-            Ok(object)
-        } else if let Some(array) = self.parse_array()? {
-            Ok(array)
-        } else if let Some(t) = self.parse_keyword("true", JSONValue::True)? {
-            Ok(t)
-        } else if let Some(f) = self.parse_keyword("false", JSONValue::False)? {
-            Ok(f)
-        } else if let Some(n) = self.parse_keyword("null", JSONValue::Null)? {
-            Ok(n)
-        } else {
-            Err(ParseError::UnexpectedEndOfInput(String::from(
-                "Doesn't seem to be valid JSON",
-            )))
-        };
+        // Go through the parser methods, until you find
+        // one that doesn't return a `None`
+        try_parse!(
+            self.parse_string(),
+            self.parse_number(),
+            self.parse_object(),
+            self.parse_array(),
+            self.parse_keyword("true", JSONValue::True),
+            self.parse_keyword("false", JSONValue::False),
+            self.parse_keyword("null", JSONValue::Null)
+        );
 
-        // Eagerly evaluated simpler alternative to the original option iterator chain
-        //        let value = self.parse_string()?
-        //            .or(self.parse_number()?)
-        //            .or(self.parse_object()?)
-        //            .or(self.parse_array()?)
-        //            .or(self.parse_keyword("true", JSONValue::True)?)
-        //            .or(self.parse_keyword("false", JSONValue::False)?)
-        //            .or(self.parse_keyword("null", JSONValue::Null)?);
+        // Every parser failed, so the syntax is probably incorrect
+        Err(ParseError::UnexpectedEndOfInput(String::from(
+            "Doesn't seem to be valid JSON",
+        )))
     }
 
     /// See if there's a `JSONValue::Object` next in the JSON
@@ -143,7 +144,7 @@ impl JSON {
                     JSONValue::String(s) => s,
                     _ => panic!("parse_string returned non-string value"),
                 },
-                None => panic!("Missing object key"),
+                None => String::new(),
             };
 
             self.skip_whitespace();