Add comments

src/lib.rs

@@ -1,51 +1,102 @@
 //! # Naive JSON Parser
+//!
+//! Based on [JSON Parser with JavaScript](https://lihautan.com/json-parser-with-javascript/)
+#![forbid(unsafe_code)]
 use std::collections::HashMap;
 use std::iter::FromIterator;
 
+/// The type of JSON value
 #[derive(Debug, PartialEq)]
 pub enum JSONValue {
+    /// Object Literal
     Object(HashMap<String, JSONValue>),
+
+    /// Array Literal
     Array(Vec<JSONValue>),
+
+    /// String Literal
     String(String),
+
+    /// Number Literal
     Number(f64),
+
+    /// True Literal
     True,
+
+    /// False Literal
     False,
+
+    /// Null Literal
     Null,
 }
 
+/// The type of error returned by the parser
 #[derive(Debug, PartialEq)]
 pub enum ParseError {
+    /// The input looks like JSON, but seems to end
     UnexpectedEndOfInput(String),
+
+    /// Looks like JSON, but seems to have characters after it should
     ExpectedEndOfInput(String),
+
+    /// Wasn't this supposed to be an object literal?
     ExpectedObjectKey(String),
+
+    /// Hey, wasn't there supposed to be...?
     ExpectedToken(String),
+
+    /// What's this character?
     UnexpectedToken(String),
+
+    /// Shouldn't this be a numeral?
     ExpectedDigit(String),
+
+    /// There's a backslash...were you going somewhere with that?
     ExpectedEscapeChar(String),
+
+    /// Should be a unicode escape character...missing a few digits?
     ExpectedUnicodeEscape(String),
 }
 
+/// This struct holds a little state for parsing
 #[derive(Debug, PartialEq)]
 pub struct JSON {
+    /// The input JSON String as a character array
     chars: Vec<char>,
-    i: usize
+
+    /// The internal parsing index
+    i: usize,
 }
 
-pub type JSONResult = Result<JSONValue, ParseError>;
-type PartialResult = Result<Option<JSONValue>, ParseError>;
-
 impl JSON {
+    /// Private constructor
     fn new(json: &str) -> Self {
-       JSON {
-           chars: json.chars().collect(),
-           i: 0
-       }
+        JSON {
+            chars: json.chars().collect(),
+            i: 0,
+        }
     }
 
-    fn parse_value(&mut self) -> JSONResult {
+    /// Parse a `JSONValue` from the current JSON string
+    ///
+    /// This is probably an abuse of iterators...but it's still much better than the alternative
+    /// of nested matches.
+    ///
+    /// In order to determine the type of JSON value, each parse method is tried, until one
+    /// matches, or a parse error happens.
+    ///
+    /// * `Option`s implement IntoIterator, which returns an iterator of -1 or 1 items: the
+    /// transferred (not borrowed) Some() value.
+    /// * The `chain` method of iterators allows you to link iterators together,
+    /// to act as one iterator
+    /// * The first result from the iterator is the first parse method with a non-empty value,
+    /// and should be the value wanted
+    fn parse_value(&mut self) -> Result<JSONValue, ParseError> {
         self.skip_whitespace();
 
-        let mut types = self.parse_string()?.into_iter()
+        let mut value = self
+            .parse_string()?
+            .into_iter()
             .chain(self.parse_number()?.into_iter())
             .chain(self.parse_object()?.into_iter())
             .chain(self.parse_array()?.into_iter())
@@ -53,13 +104,16 @@ impl JSON {
             .chain(self.parse_keyword("false", JSONValue::False)?.into_iter())
             .chain(self.parse_keyword("null", JSONValue::Null)?.into_iter());
 
-        match types.next() {
+        match value.next() {
             Some(val) => Ok(val),
-            None => Err(ParseError::UnexpectedEndOfInput(String::new()))
+            None => Err(ParseError::UnexpectedEndOfInput(String::from(
+                "Doesn't seem to be valid JSON",
+            ))),
         }
     }
 
-    fn parse_object(&mut self) -> PartialResult {
+    /// See if there's a `JSONValue::Object` next in the JSON
+    fn parse_object(&mut self) -> Result<Option<JSONValue>, ParseError> {
         if self.chars[self.i] != '{' {
             return Ok(None);
         }
@@ -85,7 +139,7 @@ impl JSON {
                     JSONValue::String(s) => s,
                     _ => panic!("parse_string returned non-string value"),
                 },
-                None => String::new()
+                None => String::new(),
             };
 
             self.skip_whitespace();
@@ -103,7 +157,8 @@ impl JSON {
         Ok(Some(JSONValue::Object(result)))
     }
 
-    fn parse_array(&mut self) -> PartialResult {
+    /// See if there's a `JSONValue::Array` next in the JSON
+    fn parse_array(&mut self) -> Result<Option<JSONValue>, ParseError> {
         if self.chars[self.i] != '[' {
             return Ok(None);
         }
@@ -129,15 +184,35 @@ impl JSON {
         Ok(Some(JSONValue::Array(result)))
     }
 
-    fn parse_string(&mut self) -> PartialResult {
-       Ok(None)
+    /// See if there's a `JSONValue::String` next in the JSON
+    fn parse_string(&mut self) -> Result<Option<JSONValue>, ParseError> {
+        if self.chars[self.i] != '"' {
+            return Ok(None);
+        }
+
+        self.i += 1;
+        let mut result = String::new();
+
+        while self.chars[self.i] != '"' {
+            if self.chars[i] == '\\' {
+
+            }
+        }
+
+        Ok(None)
     }
 
-    fn parse_number(&mut self) -> PartialResult {
-       Ok(None)
+    /// See if there's a `JSONValue::Number` next in the JSON
+    fn parse_number(&mut self) -> Result<Option<JSONValue>, ParseError> {
+        Ok(None)
     }
 
-    fn parse_keyword(&mut self, search: &str, value: JSONValue) -> PartialResult {
+    /// See if there's a `JSONValue::True`, `JSONValue::False`, or a `JSONValue::Null` next in the JSON
+    fn parse_keyword(
+        &mut self,
+        search: &str,
+        value: JSONValue,
+    ) -> Result<Option<JSONValue>, ParseError> {
         let start = self.i;
         let end = if self.i + search.len() > self.chars.len() {
             self.chars.len()
@@ -147,7 +222,7 @@ impl JSON {
 
         let slice = &String::from_iter(&self.chars[start..end]);
         if slice == search {
-           self.i += search.len();
+            self.i += search.len();
 
             return Ok(Some(value));
         }
@@ -155,12 +230,18 @@ impl JSON {
         Ok(None)
     }
 
+    /// Increment the internal index until the next character is not a whitespace character
     fn skip_whitespace(&mut self) {
         while self.chars[self.i].is_ascii_whitespace() {
             self.i += 1;
         }
     }
 
+    /// 'Eat' the specified character
+    ///
+    /// * If the next `char` matches the one passed, the internal index is incremented
+    /// * If the next `char` does not match the one passed, a `ParseError::ExpectedToken`
+    /// error is returned
     fn eat(&mut self, ch: char) -> Result<(), ParseError> {
         if self.chars[self.i] != ch {
             let msg = format!(r#"Expected "{}"."#, ch);
@@ -173,13 +254,11 @@ impl JSON {
     }
 
     /// Convert a `&str` containing JSON into a `Result<JSONValue, ParseError>`
-    pub fn parse(json: &str) -> JSONResult {
+    pub fn parse(json: &str) -> Result<JSONValue, ParseError> {
         JSON::new(json).parse_value()
     }
 }
 
-
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -213,6 +292,13 @@ mod tests {
     fn can_parse_array_of_keywords() {
         let result = JSON::parse("[true,false,null]");
 
-        assert_eq!(result, Ok(JSONValue::Array(vec![JSONValue::True, JSONValue::False, JSONValue::Null])));
+        assert_eq!(
+            result,
+            Ok(JSONValue::Array(vec![
+                JSONValue::True,
+                JSONValue::False,
+                JSONValue::Null
+            ]))
+        );
     }
 }