rs-05-json-value
0.000
Challenge · difficulty 5/5
# JSON parser to a typed value
Implement the library file **`src/lib.rs`** exposing a parser for a subset of JSON:
```rust
pub fn parse(input: &str) -> Result<Value, ParseError>
pub enum Value {
Null,
Bool(bool),
Number(f64),
Str(String),
Array(Vec<Value>),
Object(Vec<(String, Value)>),
}
pub struct ParseError { /* your fields — e.g. a message and position */ }
```
Derive `Debug`, `Clone`, and `PartialEq` for `Value` so it can be compared in tests.
Parse a single JSON value from `input` and return it as a `Value`, or `Err(ParseError)` if the
input is not valid. Support:
- **Literals**: `null`, `true`, `false`.
- **Numbers**: parsed as `f64` (integers, negatives, decimals, and exponents like `1e3`).
- **Strings**: double-quoted, with the escapes `\" \\ \/ \n \t \r \b \f` and `\uXXXX`.
- **Arrays**: `[`, comma-separated values, `]`. May be empty (`[]`).
- **Objects**: `{`, comma-separated `"key": value` members, `}`. May be empty (`{}`). **Preserve
member order** exactly as it appears in the input (hence `Vec<(String, Value)>`, not a map).
- **Whitespace** (spaces, tabs, newlines, carriage returns) is allowed and ignored between tokens.
Errors (return `Err`, do not panic):
- malformed tokens, unterminated strings, missing `:`/`,`/closing brackets;
- **trailing characters** after a complete value (e.g. `"null null"` is an error).
Tests live in `tests/` and call `challenge::parse` and `challenge::Value`.
tests/json_value.rs
use challenge::{parse, Value};
#[test]
fn parses_primitives() {
assert_eq!(parse("null"), Ok(Value::Null));
assert_eq!(parse("true"), Ok(Value::Bool(true)));
assert_eq!(parse("false"), Ok(Value::Bool(false)));
assert_eq!(parse("42"), Ok(Value::Number(42.0)));
assert_eq!(parse("-3.5"), Ok(Value::Number(-3.5)));
assert_eq!(parse("1e3"), Ok(Value::Number(1000.0)));
assert_eq!(parse("\"hi\""), Ok(Value::Str("hi".to_string())));
}
#[test]
fn ignores_surrounding_whitespace() {
assert_eq!(parse(" \n true \t "), Ok(Value::Bool(true)));
}
#[test]
fn parses_string_escapes() {
assert_eq!(parse("\"a\\nb\""), Ok(Value::Str("a\nb".to_string())));
assert_eq!(parse("\"q\\\"q\""), Ok(Value::Str("q\"q".to_string())));
}
#[test]
fn parses_empty_array_and_object() {
assert_eq!(parse("[]"), Ok(Value::Array(vec![])));
assert_eq!(parse("{}"), Ok(Value::Object(vec![])));
}
#[test]
fn parses_nested_structures() {
let parsed = parse("{\"a\": [1, 2], \"b\": {\"c\": true}}").unwrap();
let expected = Value::Object(vec![
("a".to_string(), Value::Array(vec![Value::Number(1.0), Value::Number(2.0)])),
("b".to_string(), Value::Object(vec![("c".to_string(), Value::Bool(true))])),
]);
assert_eq!(parsed, expected);
}
#[test]
fn preserves_object_member_order() {
let parsed = parse("{\"z\": 1, \"a\": 2}").unwrap();
let expected = Value::Object(vec![
("z".to_string(), Value::Number(1.0)),
("a".to_string(), Value::Number(2.0)),
]);
assert_eq!(parsed, expected);
}
#[test]
fn rejects_trailing_characters() {
assert!(parse("null null").is_err());
assert!(parse("[1, 2] x").is_err());
}
#[test]
fn rejects_malformed_input() {
assert!(parse("").is_err());
assert!(parse("[1, 2").is_err());
assert!(parse("{\"a\": }").is_err());
assert!(parse("\"unterminated").is_err());
assert!(parse("{\"a\" 1}").is_err());
}
System prompt
You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.
Proposed solution
```rust
use std::iter::Peekable;
use std::str::Chars;
#[derive(Debug, Clone, PartialEq)]
pub struct ParseError {
pub message: String,
pub position: usize,
}
impl std::fmt::Display for ParseError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "ParseError at {}: {}", self.position, self.message)
}
}
impl std::error::Error for ParseError {}
#[derive(Debug, Clone, PartialEq)]
pub enum Value {
Null,
Bool(bool),
Number(f64),
Str(String),
Array(Vec<Value>),
Object(Vec<(String, Value)>),
}
pub fn parse(input: &str) -> Result<Value, ParseError> {
let mut chars = input.chars().peekable();
let result = parse_value(&mut chars)?;
skip_whitespace(&mut chars);
if chars.peek().is_some() {
return Err(ParseError {
message: "trailing characters".to_string(),
position: input.len() - chars.as_str().len(),
});
}
Ok(result)
}
fn skip_whitespace(chars: &mut Peekable<Chars>) {
while let Some(&c) = chars.peek() {
match c {
' ' | '\t' | '\n' | '\r' => {
chars.next();
}
_ => break,
}
}
}
fn parse_value(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {
skip_whitespace(chars);
match chars.peek() {
Some(&'n') => parse_null(chars),
Some(&'t') => parse_bool(chars, true),
Some(&'f') => parse_bool(chars, false),
Some(&'"') => parse_string(chars),
Some(&'[') => parse_array(chars),
Some(&'{') => parse_object(chars),
Some(&c) => Err(ParseError {
message: format!("unexpected character '{}'", c),
position: input_position(chars),
}),
None => Err(ParseError {
message: "unexpected end of input".to_string(),
position: input_position(chars),
}),
}
}
fn parse_null(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {
let mut s = String::new();
for _ in 0..4 {
match chars.next() {
Some(c) => s.push(c),
None => return Err(ParseError {
message: "unexpected end of input".to_string(),
position: input_position(chars),
}),
}
}
if s == "null" {
Ok(Value::Null)
} else {
Err(ParseError {
message: "expected 'null'".to_string(),
position: input_position(chars),
})
}
}
fn parse_bool(chars: &mut Peekable<Chars>, expected: bool) -> Result<Value, ParseError> {
let mut s = String::new();
for _ in 0..4 {
match chars.next() {
Some(c) => s.push(c),
None => return Err(ParseError {
message: "unexpected end of input".to_string(),
position: input_position(chars),
}),
}
}
if s == "true" && expected {
Ok(Value::Bool(true))
} else if s == "false" && !expected {
Ok(Value::Bool(false))
} else {
Err(ParseError {
message: format!("expected '{}'", if expected { "true" } else { "false" }),
position: input_position(chars),
})
}
}
fn parse_string(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {
let mut result = String::new();
// consume opening quote
chars.next();
while let Some(&c) = chars.peek() {
match c {
'"' => {
chars.next();
return Ok(Value::Str(result));
}
'\\' => {
chars.next();
match chars.next() {
Some('"') => result.push('"'),
Some('\\') => result.push('\\'),
Some('/') => result.push('/'),
Some('n') => result.push('\n'),
Some('t') => result.push('\t'),
Some('r') => result.push('\r'),
Some('b') => result.push('\b'),
Some('f') => result.push('\f'),
Some('u') => {
// parse \uXXXX
let mut hex = String::new();
for _ in 0..4 {
match chars.next() {
Some(c) => hex.push(c),
None => return Err(ParseError {
message: "unexpected end of input".to_string(),
position: input_position(chars),
}),
}
}
match u16::from_str_radix(&hex, 16) {
Ok(code) => {
// UTF-16 surrogate handling
if (0xD800..=0xDFFF).contains(&code) {
// If it's a high surrogate, look for a low surrogate
if chars.peek() == Some(&'\\') {
chars.next();
if chars.peek() == Some(&'u') {
chars.next();
let mut low_hex = String::new();
for _ in 0..4 {
match chars.next() {
Some(c) => low_hex.push(c),
None => return Err(ParseError {
message: "unexpected end of input".to_string(),
position: input_position(chars),
}),
}
}
if let Ok(low_code) = u16::from_str_radix(&low_hex, 16) {
if (0xDC00..=0xDFFF).contains(&low_code) {
// Combine surrogates
let code_point = 0x10000 + ((code - 0xD800) as u32) << 10 | (low_code - 0xDC00) as u32;
result.push(char::from_u32(code_point).unwrap_or('?'));
} else {
return Err(ParseError {
message: "invalid surrogate pair".to_string(),
position: input_position(chars),
});
}
} else {
return Err(ParseError {
message: "invalid unicode escape".to_string(),
position: input_position(chars),
});
}
} else {
return Err(ParseError {
message: "invalid surrogate pair".to_string(),
position: input_position(chars),
});
}
} else {
return Err(ParseError {
message: "invalid surrogate pair".to_string(),
position: input_position(chars),
});
}
} else {
result.push(char::from_u32(code as u32).unwrap_or('?'));
}
}
Err(_) => return Err(ParseError {
message: "invalid unicode escape".to_string(),
position: input_position(chars),
}),
}
}
_ => {
return Err(ParseError {
message: "invalid escape sequence".to_string(),
position: input_position(chars),
})
}
}
}
_ => {
result.push(c);
chars.next();
}
}
}
Err(ParseError {
message: "unterminated string".to_string(),
position: input_position(chars),
})
}
fn parse_array(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {
chars.next(); // consume '['
let mut elements = Vec::new();
skip_whitespace(chars);
if chars.peek() == Some(&']') {
chars.next();
return Ok(Value::Array(elements));
}
loop {
elements.push(parse_value(chars)?);
skip_whitespace(chars);
match chars.next() {
Some(&',') => {
skip_whitespace(chars);
if chars.peek() == Some(&']') {
break;
}
}
Some(&']') => break,
Some(_) => {
return Err(ParseError {
message: "expected ',' or ']'".to_string(),
position: input_position(chars),
})
}
None => {
return Err(ParseError {
message: "unexpected end of input".to_string(),
position: input_position(chars),
})
}
}
}
Ok(Value::Array(elements))
}
fn parse_object(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {
chars.next(); // consume '{'
let mut members = Vec::new();
skip_whitespace(chars);
if chars.peek() == Some(&'}') {
chars.next();
return Ok(Value::Object(members));
}
loop {
skip_whitespace(chars);
let key = parse_string(chars)?;
skip_whitespace(chars);
match chars.next() {
Some(&':') => {
skip_whitespace(chars);
let value = parse_value(chars)?;
members.push((key, value));
skip_whitespace(chars);
match chars.next() {
Some(&',') => {
skip_whitespace(chars);
if chars.peek() == Some(&'}') {
break;
}
}
Some(&'}') => break,
Some(_) => {
return Err(ParseError {
message: "expected ',' or '}'".to_string(),
position: input_position(chars),
})
}
None => {
return Err(ParseError {
message: "unexpected end of input".to_string(),
position: input_position(chars),
})
}
}
}
Some(_) => {
return Err(ParseError {
message: "expected ':'".to_string(),
position: input_position(chars),
})
}
None => {
return Err(ParseError {
message: "unexpected end of input".to_string(),
position: input_position(chars),
})
}
}
}
Ok(Value::Object(members))
}
fn input_position(chars: &mut Peekable<Chars>) -> usize {
chars.as_str().len()
}
```Errors (stderr)
error: unknown character escape: `b`
--> src/lib.rs:135:48
|
135 | Some('b') => result.push('\b'),
| ^ unknown character escape
|
= help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
help: if you meant to write a literal backslash (perhaps escaping in a regular expression), consider a raw string literal
|
135 - Some('b') => result.push('\b'),
135 + Some('b') => result.push(r"\b"),
|
error: unknown character escape: `f`
--> src/lib.rs:136:48
|
136 | Some('f') => result.push('\f'),
| ^ unknown character escape
|
= help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
help: if you meant to write a literal backslash (perhaps escaping in a regular expression), consider a raw string literal
|
136 - Some('f') => result.push('\f'),
136 + Some('f') => result.push(r"\f"),
|
error[E0599]: no method named `as_str` found for struct `Peekable<I>` in the current scope
--> src/lib.rs:35:43
|
35 | position: input.len() - chars.as_str().len(),
| ^^^^^^ method not found in `Peekable<Chars<'_>>`
error[E0308]: mismatched types
--> src/lib.rs:239:18
|
238 | match chars.next() {
| ------------ this expression has type `Option<char>`
239 | Some(&',') => {
| ^^^^ expected `char`, found `&_`
|
= note: expected type `char`
found reference `&_`
error[E0308]: mismatched types
--> src/lib.rs:245:18
|
238 | match chars.next() {
| ------------ this expression has type `Option<char>`
...
245 | Some(&']') => break,
| ^^^^ expected `char`, found `&_`
|
= note: expected type `char`
found reference `&_`
error[E0308]: mismatched types
--> src/lib.rs:276:18
|
275 | match chars.next() {
| ------------ this expression has type `Option<char>`
276 | Some(&':') => {
| ^^^^ expected `char`, found `&_`
|
= note: expected type `char`
found reference `&_`
error[E0308]: mismatched types
--> src/lib.rs:279:31
|
279 | members.push((key, value));
| ^^^ expected `String`, found `Value`
error[E0308]: mismatched types
--> src/lib.rs:282:26
|
281 | match chars.next() {
| ------------ this expression has type `Option<char>`
282 | Some(&',') => {
| ^^^^ expected `char`, found `&_`
|
= note: expected type `char`
found reference `&_`
error[E0308]: mismatched types
--> src/lib.rs:288:26
|
281 | match chars.next() {
| ------------ this expression has type `Option<char>`
...
288 | Some(&'}') => break,
| ^^^^ expected `char`, found `&_`
|
= note: expected type `char`
found reference `&_`
error[E0599]: no method named `as_str` found for mutable reference `&mut Peekable<Chars<'_>>` in the current scope
--> src/lib.rs:321:11
|
321 | chars.as_str().len()
| ^^^^^^ method not found in `&mut Peekable<Chars<'_>>`
Some errors have detailed explanations: E0308, E0599.
For more information about an error, try `rustc --explain E0308`.
error: could not compile `challenge` (lib) due to 10 previous errors
error: could not compile `challenge` (lib test) due to 10 previous errors
Self-repair attempts
[
{
"total": 1,
"answer": "```rust\nuse std::iter::Peekable;\nuse std::str::Chars;\n\n#[derive(Debug, Clone, PartialEq)]\npub struct ParseError {\n pub message: String,\n pub position: usize,\n}\n\nimpl std::fmt::Display for ParseError {\n fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {\n write!(f, \"ParseError at {}: {}\", self.position, self.message)\n }\n}\n\nimpl std::error::Error for ParseError {}\n\n#[derive(Debug, Clone, PartialEq)]\npub enum Value {\n Null,\n Bool(bool),\n Number(f64),\n Str(String),\n Array(Vec<Value>),\n Object(Vec<(String, Value)>),\n}\n\npub fn parse(input: &str) -> Result<Value, ParseError> {\n let mut chars = input.chars().peekable();\n let result = parse_value(&mut chars)?;\n skip_whitespace(&mut chars);\n if chars.peek().is_some() {\n return Err(ParseError {\n message: \"trailing characters\".to_string(),\n position: input.len() - chars.as_str().len(),\n });\n }\n Ok(result)\n}\n\nfn skip_whitespace(chars: &mut Peekable<Chars>) {\n while let Some(&c) = chars.peek() {\n match c {\n ' ' | '\\t' | '\\n' | '\\r' => {\n chars.next();\n }\n _ => break,\n }\n }\n}\n\nfn parse_value(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n skip_whitespace(chars);\n match chars.peek() {\n Some(&'n') => parse_null(chars),\n Some(&'t') => parse_bool(chars, true),\n Some(&'f') => parse_bool(chars, false),\n Some(&'\"') => parse_string(chars),\n Some(&'[') => parse_array(chars),\n Some(&'{') => parse_object(chars),\n Some(&c) => Err(ParseError {\n message: format!(\"unexpected character '{}'\", c),\n position: input_position(chars),\n }),\n None => Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n}\n\nfn parse_null(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n let mut s = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => s.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n if s == \"null\" {\n Ok(Value::Null)\n } else {\n Err(ParseError {\n message: \"expected 'null'\".to_string(),\n position: input_position(chars),\n })\n }\n}\n\nfn parse_bool(chars: &mut Peekable<Chars>, expected: bool) -> Result<Value, ParseError> {\n let mut s = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => s.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n if s == \"true\" && expected {\n Ok(Value::Bool(true))\n } else if s == \"false\" && !expected {\n Ok(Value::Bool(false))\n } else {\n Err(ParseError {\n message: format!(\"expected '{}'\", if expected { \"true\" } else { \"false\" }),\n position: input_position(chars),\n })\n }\n}\n\nfn parse_string(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n let mut result = String::new();\n // consume opening quote\n chars.next();\n while let Some(&c) = chars.peek() {\n match c {\n '\"' => {\n chars.next();\n return Ok(Value::Str(result));\n }\n '\\\\' => {\n chars.next();\n match chars.next() {\n Some('\"') => result.push('\"'),\n Some('\\\\') => result.push('\\\\'),\n Some('/') => result.push('/'),\n Some('n') => result.push('\\n'),\n Some('t') => result.push('\\t'),\n Some('r') => result.push('\\r'),\n Some('b') => result.push('\\b'),\n Some('f') => result.push('\\f'),\n Some('u') => {\n // parse \\uXXXX\n let mut hex = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => hex.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n match u16::from_str_radix(&hex, 16) {\n Ok(code) => {\n // UTF-16 surrogate handling\n if (0xD800..=0xDFFF).contains(&code) {\n // If it's a high surrogate, look for a low surrogate\n if chars.peek() == Some(&'\\\\') {\n chars.next();\n if chars.peek() == Some(&'u') {\n chars.next();\n let mut low_hex = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => low_hex.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n if let Ok(low_code) = u16::from_str_radix(&low_hex, 16) {\n if (0xDC00..=0xDFFF).contains(&low_code) {\n // Combine surrogates\n let code_point = 0x10000 + ((code - 0xD800) as u32) << 10 | (low_code - 0xDC00) as u32;\n result.push(char::from_u32(code_point).unwrap_or('?'));\n } else {\n return Err(ParseError {\n message: \"invalid surrogate pair\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n return Err(ParseError {\n message: \"invalid unicode escape\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n return Err(ParseError {\n message: \"invalid surrogate pair\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n return Err(ParseError {\n message: \"invalid surrogate pair\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n result.push(char::from_u32(code as u32).unwrap_or('?'));\n }\n }\n Err(_) => return Err(ParseError {\n message: \"invalid unicode escape\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n _ => {\n return Err(ParseError {\n message: \"invalid escape sequence\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n _ => {\n result.push(c);\n chars.next();\n }\n }\n }\n Err(ParseError {\n message: \"unterminated string\".to_string(),\n position: input_position(chars),\n })\n}\n\nfn parse_array(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n chars.next(); // consume '['\n let mut elements = Vec::new();\n skip_whitespace(chars);\n if chars.peek() == Some(&']') {\n chars.next();\n return Ok(Value::Array(elements));\n }\n loop {\n elements.push(parse_value(chars)?);\n skip_whitespace(chars);\n match chars.next() {\n Some(&',') => {\n skip_whitespace(chars);\n if chars.peek() == Some(&']') {\n break;\n }\n }\n Some(&']') => break,\n Some(_) => {\n return Err(ParseError {\n message: \"expected ',' or ']'\".to_string(),\n position: input_position(chars),\n })\n }\n None => {\n return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n Ok(Value::Array(elements))\n}\n\nfn parse_object(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n chars.next(); // consume '{'\n let mut members = Vec::new();\n skip_whitespace(chars);\n if chars.peek() == Some(&'}') {\n chars.next();\n return Ok(Value::Object(members));\n }\n loop {\n skip_whitespace(chars);\n let key = parse_string(chars)?;\n skip_whitespace(chars);\n match chars.next() {\n Some(&':') => {\n skip_whitespace(chars);\n let value = parse_value(chars)?;\n members.push((key, value));\n skip_whitespace(chars);\n match chars.next() {\n Some(&',') => {\n skip_whitespace(chars);\n if chars.peek() == Some(&'}') {\n break;\n }\n }\n Some(&'}') => break,\n Some(_) => {\n return Err(ParseError {\n message: \"expected ',' or '}'\".to_string(),\n position: input_position(chars),\n })\n }\n None => {\n return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n Some(_) => {\n return Err(ParseError {\n message: \"expected ':'\".to_string(),\n position: input_position(chars),\n })\n }\n None => {\n return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n Ok(Value::Object(members))\n}\n\nfn input_position(chars: &mut Peekable<Chars>) -> usize {\n chars.as_str().len()\n}\n```",
"passed": 0,
"test_error": "^^^ method not found in `Peekable<Chars<'_>>`\n\nerror[E0308]: mismatched types\n --> src/lib.rs:239:18\n |\n238 | match chars.next() {\n | ------------ this expression has type `Option<char>`\n239 | Some(&',') => {\n | ^^^^ expected `char`, found `&_`\n |\n = note: expected type `char`\n found reference `&_`\n\nerror[E0308]: mismatched types\n --> src/lib.rs:245:18\n |\n238 | match chars.next() {\n | ------------ this expression has type `Option<char>`\n...\n245 | Some(&']') => break,\n | ^^^^ expected `char`, found `&_`\n |\n = note: expected type `char`\n found reference `&_`\n\nerror[E0308]: mismatched types\n --> src/lib.rs:276:18\n |\n275 | match chars.next() {\n | ------------ this expression has type `Option<char>`\n276 | Some(&':') => {\n | ^^^^ expected `char`, found `&_`\n |\n = note: expected type `char`\n found reference `&_`\n\nerror[E0308]: mismatched types\n --> src/lib.rs:279:31\n |\n279 | members.push((key, value));\n | ^^^ expected `String`, found `Value`\n\nerror[E0308]: mismatched types\n --> src/lib.rs:282:26\n |\n281 | match chars.next() {\n | ------------ this expression has type `Option<char>`\n282 | Some(&',') => {\n | ^^^^ expected `char`, found `&_`\n |\n = note: expected type `char`\n found reference `&_`\n\nerror[E0308]: mismatched types\n --> src/lib.rs:288:26\n |\n281 | match chars.next() {\n | ------------ this expression has type `Option<char>`\n...\n288 | Some(&'}') => break,\n | ^^^^ expected `char`, found `&_`\n |\n = note: expected type `char`\n found reference `&_`\n\nerror[E0599]: no method named `as_str` found for mutable reference `&mut Peekable<Chars<'_>>` in the current scope\n --> src/lib.rs:321:11\n |\n321 | chars.as_str().len()\n | ^^^^^^ method not found in `&mut Peekable<Chars<'_>>`\n\nSome errors have detailed explanations: E0308, E0599.\nFor more information about an error, try `rustc --explain E0308`.\nerror: could not compile `challenge` (lib) due to 10 previous errors\nerror: could not compile `challenge` (lib test) due to 10 previous errors"
},
{
"total": 1,
"answer": "```rust\nuse std::iter::Peekable;\nuse std::str::Chars;\n\n#[derive(Debug, Clone, PartialEq)]\npub struct ParseError {\n pub message: String,\n pub position: usize,\n}\n\nimpl std::fmt::Display for ParseError {\n fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {\n write!(f, \"ParseError at {}: {}\", self.position, self.message)\n }\n}\n\nimpl std::error::Error for ParseError {}\n\n#[derive(Debug, Clone, PartialEq)]\npub enum Value {\n Null,\n Bool(bool),\n Number(f64),\n Str(String),\n Array(Vec<Value>),\n Object(Vec<(String, Value)>),\n}\n\npub fn parse(input: &str) -> Result<Value, ParseError> {\n let mut chars = input.chars().peekable();\n let result = parse_value(&mut chars)?;\n skip_whitespace(&mut chars);\n if chars.peek().is_some() {\n return Err(ParseError {\n message: \"trailing characters\".to_string(),\n position: input_position(&mut chars),\n });\n }\n Ok(result)\n}\n\nfn skip_whitespace(chars: &mut Peekable<Chars>) {\n while let Some(&c) = chars.peek() {\n match c {\n ' ' | '\\t' | '\\n' | '\\r' => {\n chars.next();\n }\n _ => break,\n }\n }\n}\n\nfn parse_value(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n skip_whitespace(chars);\n match chars.peek() {\n Some(&'n') => parse_null(chars),\n Some(&'t') => parse_bool(chars, true),\n Some(&'f') => parse_bool(chars, false),\n Some(&'\"') => parse_string(chars),\n Some(&'[') => parse_array(chars),\n Some(&'{') => parse_object(chars),\n Some(&c) => Err(ParseError {\n message: format!(\"unexpected character '{}'\", c),\n position: input_position(chars),\n }),\n None => Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n}\n\nfn parse_null(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n let mut s = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => s.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n if s == \"null\" {\n Ok(Value::Null)\n } else {\n Err(ParseError {\n message: \"expected 'null'\".to_string(),\n position: input_position(chars),\n })\n }\n}\n\nfn parse_bool(chars: &mut Peekable<Chars>, expected: bool) -> Result<Value, ParseError> {\n let mut s = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => s.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n if s == \"true\" && expected {\n Ok(Value::Bool(true))\n } else if s == \"false\" && !expected {\n Ok(Value::Bool(false))\n } else {\n Err(ParseError {\n message: format!(\"expected '{}'\", if expected { \"true\" } else { \"false\" }),\n position: input_position(chars),\n })\n }\n}\n\nfn parse_string(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n let mut result = String::new();\n // consume opening quote\n chars.next();\n while let Some(&c) = chars.peek() {\n match c {\n '\"' => {\n chars.next();\n return Ok(Value::Str(result));\n }\n '\\\\' => {\n chars.next();\n match chars.next() {\n Some('\"') => result.push('\"'),\n Some('\\\\') => result.push('\\\\'),\n Some('/') => result.push('/'),\n Some('n') => result.push('\\n'),\n Some('t') => result.push('\\t'),\n Some('r') => result.push('\\r'),\n Some('b') => result.push('\\b'),\n Some('f') => result.push('\\f'),\n Some('u') => {\n // parse \\uXXXX\n let mut hex = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => hex.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n match u16::from_str_radix(&hex, 16) {\n Ok(code) => {\n // UTF-16 surrogate handling\n if (0xD800..=0xDFFF).contains(&code) {\n // If it's a high surrogate, look for a low surrogate\n if chars.peek() == Some(&'\\\\') {\n chars.next();\n if chars.peek() == Some(&'u') {\n chars.next();\n let mut low_hex = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => low_hex.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n if let Ok(low_code) = u16::from_str_radix(&low_hex, 16) {\n if (0xDC00..=0xDFFF).contains(&low_code) {\n // Combine surrogates\n let code_point = 0x10000 + ((code - 0xD800) as u32) << 10 | (low_code - 0xDC00) as u32;\n result.push(char::from_u32(code_point).unwrap_or('?'));\n } else {\n return Err(ParseError {\n message: \"invalid surrogate pair\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n return Err(ParseError {\n message: \"invalid unicode escape\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n return Err(ParseError {\n message: \"invalid surrogate pair\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n return Err(ParseError {\n message: \"invalid surrogate pair\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n result.push(char::from_u32(code as u32).unwrap_or('?'));\n }\n }\n Err(_) => return Err(ParseError {\n message: \"invalid unicode escape\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n _ => {\n return Err(ParseError {\n message: \"invalid escape sequence\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n _ => {\n result.push(c);\n chars.next();\n }\n }\n }\n Err(ParseError {\n message: \"unterminated string\".to_string(),\n position: input_position(chars),\n })\n}\n\nfn parse_array(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n chars.next(); // consume '['\n let mut elements = Vec::new();\n skip_whitespace(chars);\n if chars.peek() == Some(&']') {\n chars.next();\n return Ok(Value::Array(elements));\n }\n loop {\n elements.push(parse_value(chars)?);\n skip_whitespace(chars);\n match chars.next() {\n Some(',') => {\n skip_whitespace(chars);\n if chars.peek() == Some(&']') {\n break;\n }\n }\n Some(']') => break,\n Some(_) => {\n return Err(ParseError {\n message: \"expected ',' or ']'\".to_string(),\n position: input_position(chars),\n })\n }\n None => {\n return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n Ok(Value::Array(elements))\n}\n\nfn parse_object(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n chars.next(); // consume '{'\n let mut members = Vec::new();\n skip_whitespace(chars);\n if chars.peek() == Some(&'}') {\n chars.next();\n return Ok(Value::Object(members));\n }\n loop {\n skip_whitespace(chars);\n let key = parse_string(chars)?;\n skip_whitespace(chars);\n match chars.next() {\n Some(':') => {\n skip_whitespace(chars);\n let value = parse_value(chars)?;\n members.push((key, value));\n skip_whitespace(chars);\n match chars.next() {\n Some(',') => {\n skip_whitespace(chars);\n if chars.peek() == Some(&'}') {\n break;\n }\n }\n Some('}') => break,\n Some(_) => {\n return Err(ParseError {\n message: \"expected ',' or '}'\".to_string(),\n position: input_position(chars),\n })\n }\n None => {\n return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n Some(_) => {\n return Err(ParseError {\n message: \"expected ':'\".to_string(),\n position: input_position(chars),\n })\n }\n None => {\n return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n Ok(Value::Object(members))\n}\n\nfn input_position(chars: &mut Peekable<Chars>) -> usize {\n let mut pos = 0;\n for c in chars {\n pos += c.len_utf8();\n }\n pos\n}\n```",
"passed": 0,
"test_error": "error: unknown character escape: `b`\n --> src/lib.rs:135:48\n |\n135 | Some('b') => result.push('\\b'),\n | ^ unknown character escape\n |\n = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>\nhelp: if you meant to write a literal backslash (perhaps escaping in a regular expression), consider a raw string literal\n |\n135 - Some('b') => result.push('\\b'),\n135 + Some('b') => result.push(r\"\\b\"),\n |\n\nerror: unknown character escape: `f`\n --> src/lib.rs:136:48\n |\n136 | Some('f') => result.push('\\f'),\n | ^ unknown character escape\n |\n = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>\nhelp: if you meant to write a literal backslash (perhaps escaping in a regular expression), consider a raw string literal\n |\n136 - Some('f') => result.push('\\f'),\n136 + Some('f') => result.push(r\"\\f\"),\n |\n\nerror[E0308]: mismatched types\n --> src/lib.rs:279:31\n |\n279 | members.push((key, value));\n | ^^^ expected `String`, found `Value`\n\nFor more information about this error, try `rustc --explain E0308`.\nerror: could not compile `challenge` (lib test) due to 3 previous errors\nerror: could not compile `challenge` (lib) due to 3 previous errors"
},
{
"total": 1,
"answer": "```rust\nuse std::iter::Peekable;\nuse std::str::Chars;\n\n#[derive(Debug, Clone, PartialEq)]\npub struct ParseError {\n pub message: String,\n pub position: usize,\n}\n\nimpl std::fmt::Display for ParseError {\n fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {\n write!(f, \"ParseError at {}: {}\", self.position, self.message)\n }\n}\n\nimpl std::error::Error for ParseError {}\n\n#[derive(Debug, Clone, PartialEq)]\npub enum Value {\n Null,\n Bool(bool),\n Number(f64),\n Str(String),\n Array(Vec<Value>),\n Object(Vec<(String, Value)>),\n}\n\npub fn parse(input: &str) -> Result<Value, ParseError> {\n let mut chars = input.chars().peekable();\n let result = parse_value(&mut chars)?;\n skip_whitespace(&mut chars);\n if chars.peek().is_some() {\n return Err(ParseError {\n message: \"trailing characters\".to_string(),\n position: input_position(&mut chars),\n });\n }\n Ok(result)\n}\n\nfn skip_whitespace(chars: &mut Peekable<Chars>) {\n while let Some(&c) = chars.peek() {\n match c {\n ' ' | '\\t' | '\\n' | '\\r' => {\n chars.next();\n }\n _ => break,\n }\n }\n}\n\nfn parse_value(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n skip_whitespace(chars);\n match chars.peek() {\n Some(&'n') => parse_null(chars),\n Some(&'t') => parse_bool(chars, true),\n Some(&'f') => parse_bool(chars, false),\n Some(&'\"') => parse_string(chars),\n Some(&'[') => parse_array(chars),\n Some(&'{') => parse_object(chars),\n Some(&c) => Err(ParseError {\n message: format!(\"unexpected character '{}'\", c),\n position: input_position(chars),\n }),\n None => Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n}\n\nfn parse_null(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n let mut s = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => s.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n if s == \"null\" {\n Ok(Value::Null)\n } else {\n Err(ParseError {\n message: \"expected 'null'\".to_string(),\n position: input_position(chars),\n })\n }\n}\n\nfn parse_bool(chars: &mut Peekable<Chars>, expected: bool) -> Result<Value, ParseError> {\n let mut s = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => s.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n if s == \"true\" && expected {\n Ok(Value::Bool(true))\n } else if s == \"false\" && !expected {\n Ok(Value::Bool(false))\n } else {\n Err(ParseError {\n message: format!(\"expected '{}'\", if expected { \"true\" } else { \"false\" }),\n position: input_position(chars),\n })\n }\n}\n\nfn parse_string(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n let mut result = String::new();\n // consume opening quote\n chars.next();\n while let Some(&c) = chars.peek() {\n match c {\n '\"' => {\n chars.next();\n return Ok(Value::Str(result));\n }\n '\\\\' => {\n chars.next();\n match chars.next() {\n Some('\"') => result.push('\"'),\n Some('\\\\') => result.push('\\\\'),\n Some('/') => result.push('/'),\n Some('n') => result.push('\\n'),\n Some('t') => result.push('\\t'),\n Some('r') => result.push('\\r'),\n Some('b') => result.push('\\x08'),\n Some('f') => result.push('\\x0c'),\n Some('u') => {\n // parse \\uXXXX\n let mut hex = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => hex.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n match u16::from_str_radix(&hex, 16) {\n Ok(code) => {\n // UTF-16 surrogate handling\n if (0xD800..=0xDFFF).contains(&code) {\n // If it's a high surrogate, look for a low surrogate\n if chars.peek() == Some(&'\\\\') {\n chars.next();\n if chars.peek() == Some(&'u') {\n chars.next();\n let mut low_hex = String::new();\n for _ in 0..4 {\n match chars.next() {\n Some(c) => low_hex.push(c),\n None => return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n if let Ok(low_code) = u16::from_str_radix(&low_hex, 16) {\n if (0xDC00..=0xDFFF).contains(&low_code) {\n // Combine surrogates\n let code_point = 0x10000 + ((code - 0xD800) as u32) << 10 | (low_code - 0xDC00) as u32;\n result.push(char::from_u32(code_point).unwrap_or('?'));\n } else {\n return Err(ParseError {\n message: \"invalid surrogate pair\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n return Err(ParseError {\n message: \"invalid unicode escape\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n return Err(ParseError {\n message: \"invalid surrogate pair\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n return Err(ParseError {\n message: \"invalid surrogate pair\".to_string(),\n position: input_position(chars),\n });\n }\n } else {\n result.push(char::from_u32(code as u32).unwrap_or('?'));\n }\n }\n Err(_) => return Err(ParseError {\n message: \"invalid unicode escape\".to_string(),\n position: input_position(chars),\n }),\n }\n }\n _ => {\n return Err(ParseError {\n message: \"invalid escape sequence\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n _ => {\n result.push(c);\n chars.next();\n }\n }\n }\n Err(ParseError {\n message: \"unterminated string\".to_string(),\n position: input_position(chars),\n })\n}\n\nfn parse_array(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n chars.next(); // consume '['\n let mut elements = Vec::new();\n skip_whitespace(chars);\n if chars.peek() == Some(&']') {\n chars.next();\n return Ok(Value::Array(elements));\n }\n loop {\n elements.push(parse_value(chars)?);\n skip_whitespace(chars);\n match chars.next() {\n Some(',') => {\n skip_whitespace(chars);\n if chars.peek() == Some(&']') {\n break;\n }\n }\n Some(']') => break,\n Some(_) => {\n return Err(ParseError {\n message: \"expected ',' or ']'\".to_string(),\n position: input_position(chars),\n })\n }\n None => {\n return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n Ok(Value::Array(elements))\n}\n\nfn parse_object(chars: &mut Peekable<Chars>) -> Result<Value, ParseError> {\n chars.next(); // consume '{'\n let mut members = Vec::new();\n skip_whitespace(chars);\n if chars.peek() == Some(&'}') {\n chars.next();\n return Ok(Value::Object(members));\n }\n loop {\n skip_whitespace(chars);\n let key = parse_string(chars)?;\n skip_whitespace(chars);\n match chars.next() {\n Some(':') => {\n skip_whitespace(chars);\n let value = parse_value(chars)?;\n members.push((key, value));\n skip_whitespace(chars);\n match chars.next() {\n Some(',') => {\n skip_whitespace(chars);\n if chars.peek() == Some(&'}') {\n break;\n }\n }\n Some('}') => break,\n Some(_) => {\n return Err(ParseError {\n message: \"expected ',' or '}'\".to_string(),\n position: input_position(chars),\n })\n }\n None => {\n return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n Some(_) => {\n return Err(ParseError {\n message: \"expected ':'\".to_string(),\n position: input_position(chars),\n })\n }\n None => {\n return Err(ParseError {\n message: \"unexpected end of input\".to_string(),\n position: input_position(chars),\n })\n }\n }\n }\n Ok(Value::Object(members))\n}\n\nfn input_position(chars: &mut Peekable<Chars>) -> usize {\n let mut pos = 0;\n for c in chars {\n pos += c.len_utf8();\n }\n pos\n}\n```",
"passed": 0,
"test_error": ""
}
]