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//! String and character literal parsing utilities for Lambdust.
//!
//! This module provides comprehensive parsing and validation for string literals
//! and character literals according to R7RS Scheme specification, including:
//! - String escape sequences (basic and Unicode)
//! - Character literals (named and Unicode)
//! - Proper error handling with detailed diagnostics
use crate::diagnostics::{Error, Result, Span};
/// Validates string escape sequences in a string literal content.
/// The input should be the string content without the surrounding quotes.
pub fn validate_string_escapes(content: &str, span: Span) -> Result<()> {
let mut chars = content.char_indices();
while let Some((_i, ch)) = chars.next() {
if ch == '\\' {
match chars.next() {
Some((_, escape_ch)) => {
match escape_ch {
// Standard escape sequences
'"' | '\\' | 'a' | 'b' | 'f' | 'n' | 'r' | 't' | 'v' => {
// Valid escape sequence
}
// Unicode hex escape: \xHHHH... (terminated by ;)
'x' => {
let mut hex_digits = String::new();
let mut found_semicolon = false;
for (_, hex_ch) in chars.by_ref() {
if hex_ch == ';' {
found_semicolon = true;
break;
} else if hex_ch.is_ascii_hexdigit() {
hex_digits.push(hex_ch);
if hex_digits.len() > 6 {
return Err(Box::new(Error::lex_error(
"Unicode escape sequence too long (max 6 digits)",
span,
)))
}
} else {
return Err(Box::new(Error::lex_error(
format!("Invalid character in Unicode escape: '{hex_ch}'"),
span,
)))
}
}
if !found_semicolon {
return Err(Box::new(Error::lex_error(
"Unicode escape sequence must end with ';'",
span,
)))
}
if hex_digits.is_empty() {
return Err(Box::new(Error::lex_error(
"Unicode escape sequence must have at least one digit",
span,
)))
}
// Validate the Unicode code point
if let Ok(code_point) = u32::from_str_radix(&hex_digits, 16) {
if code_point > 0x10FFFF {
return Err(Box::new(Error::lex_error(
"Unicode code point out of range (max 0x10FFFF)",
span,
)))
}
// Check for surrogate pairs (invalid in Unicode)
if (0xD800..=0xDFFF).contains(&code_point) {
return Err(Box::new(Error::lex_error(
"Unicode surrogate code points are not allowed",
span,
)))
}
} else {
return Err(Box::new(Error::lex_error(
"Invalid Unicode escape sequence",
span,
)))
}
}
// Octal escape: \NNN (1-3 octal digits)
ch if ch.is_ascii_digit() && ('0'..='7').contains(&ch) => {
let mut octal_digits = String::new();
octal_digits.push(ch);
// Look ahead for up to 2 more octal digits
let mut peek_chars = chars.clone();
for _ in 0..2 {
if let Some((_, next_ch)) = peek_chars.next() {
if ('0'..='7').contains(&next_ch) {
octal_digits.push(next_ch);
chars.next(); // Consume the character
} else {
break;
}
} else {
break;
}
}
// Validate octal value
if let Ok(_octal_value) = u8::from_str_radix(&octal_digits, 8) {
// u8 values are always <= 255, so no additional check needed
} else {
return Err(Box::new(Error::lex_error(
"Invalid octal escape sequence",
span,
)))
}
}
_ => {
return Err(Box::new(Error::lex_error(
format!("Invalid escape sequence: '\\{escape_ch}'"),
span,
)))
}
}
},
None => {
return Err(Box::new(Error::lex_error(
"String literal ends with incomplete escape sequence",
span,
)))
}
}
}
}
Ok(())
}
/// Validates a character literal (without the #\\ prefix).
pub fn validate_character_literal(content: &str, span: Span) -> Result<()> {
if content.is_empty() {
return Err(Box::new(Error::lex_error("Empty character literal", span)))
}
// Check for named characters
match content {
"alarm" | "backspace" | "delete" | "escape" | "newline" |
"null" | "return" | "space" | "tab" | "vtab" => {
return Ok(());
}
_ => {}
}
// Check for Unicode hex escape
if let Some(hex_part) = content.strip_prefix('x') {
if hex_part.is_empty() {
return Err(Box::new(Error::lex_error(
"Unicode character literal must have hex digits after 'x'",
span,
)))
}
for ch in hex_part.chars() {
if !ch.is_ascii_hexdigit() {
return Err(Box::new(Error::lex_error(
format!("Invalid hex digit in character literal: '{ch}'"),
span,
)))
}
}
// Validate the Unicode code point
if let Ok(code_point) = u32::from_str_radix(hex_part, 16) {
if code_point > 0x10FFFF {
return Err(Box::new(Error::lex_error(
"Unicode code point out of range (max 0x10FFFF)",
span,
)))
}
// Check for surrogate pairs
if (0xD800..=0xDFFF).contains(&code_point) {
return Err(Box::new(Error::lex_error(
"Unicode surrogate code points are not allowed",
span,
)))
}
} else {
return Err(Box::new(Error::lex_error(
"Invalid Unicode character literal",
span,
)))
}
return Ok(());
}
// Single character
let mut chars = content.chars();
let first_char = chars.next().unwrap();
if chars.next().is_some() {
return Err(Box::new(Error::lex_error(
"Character literal can only contain one character or a named character",
span,
)))
}
// Check for valid character
if first_char.is_control() && !matches!(first_char, '\t' | '\n' | '\r') {
return Err(Box::new(Error::lex_error(
"Control characters in character literals must use named forms",
span,
)))
}
Ok(())
}
/// Unescapes a string literal content, converting escape sequences to their actual values.
pub fn unescape_string(content: &str) -> Result<String> {
let mut result = String::new();
let mut chars = content.char_indices();
while let Some((_, ch)) = chars.next() {
if ch == '\\' {
match chars.next() {
Some((_, escape_ch)) => {
match escape_ch {
'"' => result.push('"'),
'\\' => result.push('\\'),
'a' => result.push('\x07'), // Alert (bell)
'b' => result.push('\x08'), // Backspace
'f' => result.push('\x0C'), // Form feed
'n' => result.push('\n'), // Newline
'r' => result.push('\r'), // Carriage return
't' => result.push('\t'), // Tab
'v' => result.push('\x0B'), // Vertical tab
'x' => {
// Unicode hex escape
let mut hex_digits = String::new();
for (_, hex_ch) in chars.by_ref() {
if hex_ch == ';' {
break;
} else {
hex_digits.push(hex_ch);
}
}
let code_point = u32::from_str_radix(&hex_digits, 16)
.map_err(|_| Error::internal_error("Invalid Unicode escape during unescaping"))?;
let unicode_char = char::from_u32(code_point)
.ok_or_else(|| Error::internal_error("Invalid Unicode code point during unescaping"))?;
result.push(unicode_char);
}
ch if ch.is_ascii_digit() && ('0'..='7').contains(&ch) => {
// Octal escape
let mut octal_digits = String::new();
octal_digits.push(ch);
// Look for up to 2 more octal digits
let mut peek_chars = chars.clone();
for _ in 0..2 {
if let Some((_, next_ch)) = peek_chars.next() {
if ('0'..='7').contains(&next_ch) {
octal_digits.push(next_ch);
chars.next(); // Consume
} else {
break;
}
} else {
break;
}
}
let octal_value = u8::from_str_radix(&octal_digits, 8)
.map_err(|_| Error::internal_error("Invalid octal escape during unescaping"))?;
result.push(octal_value as char);
}
_ => {
return Err(Box::new(Error::internal_error(
format!("Unknown escape sequence during unescaping: \\{escape_ch}")
)))
}
}
}
None => {
return Err(Box::new(Error::internal_error(
"Incomplete escape sequence during unescaping"
)))
}
}
} else {
result.push(ch);
}
}
Ok(result)
}
/// Converts a character literal to its character value.
pub fn parse_character_literal(content: &str) -> Result<char> {
// Handle named characters
match content {
"alarm" => return Ok('\x07'),
"backspace" => return Ok('\x08'),
"delete" => return Ok('\x7F'),
"escape" => return Ok('\x1B'),
"newline" => return Ok('\n'),
"null" => return Ok('\0'),
"return" => return Ok('\r'),
"space" => return Ok(' '),
"tab" => return Ok('\t'),
"vtab" => return Ok('\x0B'),
_ => {}
}
// Handle Unicode hex escape
if let Some(hex_part) = content.strip_prefix('x') {
let code_point = u32::from_str_radix(hex_part, 16)
.map_err(|_| Error::internal_error("Invalid Unicode character literal during parsing"))?;
return char::from_u32(code_point)
.ok_or_else(|| Error::internal_error("Invalid Unicode code point during character parsing")).map_err(Box::new)
}
// Single character
let mut chars = content.chars();
let ch = chars.next()
.ok_or_else(|| Error::internal_error("Empty character literal during parsing"))?;
if chars.next().is_some() {
return Err(Box::new(Error::internal_error("Multiple characters in character literal during parsing")));
}
Ok(ch)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_string_escape_validation() {
let span = Span::new(0, 10);
// Valid escape sequences
assert!(validate_string_escapes(r#"hello\nworld"#, span).is_ok());
assert!(validate_string_escapes(r#"quote: \""#, span).is_ok());
assert!(validate_string_escapes(r#"backslash: \\"#, span).is_ok());
assert!(validate_string_escapes(r#"unicode: \x41;"#, span).is_ok());
assert!(validate_string_escapes(r#"octal: \101"#, span).is_ok());
// Invalid escape sequences
assert!(validate_string_escapes(r#"invalid: \z"#, span).is_err());
assert!(validate_string_escapes(r#"incomplete: \"#, span).is_err());
assert!(validate_string_escapes(r#"bad unicode: \x;"#, span).is_err());
assert!(validate_string_escapes(r#"bad unicode: \xGG;"#, span).is_err());
}
#[test]
fn test_character_literal_validation() {
let span = Span::new(0, 5);
// Valid character literals
assert!(validate_character_literal("a", span).is_ok());
assert!(validate_character_literal("space", span).is_ok());
assert!(validate_character_literal("newline", span).is_ok());
assert!(validate_character_literal("x41", span).is_ok());
// Invalid character literals
assert!(validate_character_literal("", span).is_err());
assert!(validate_character_literal("ab", span).is_err());
assert!(validate_character_literal("invalid_name", span).is_err());
assert!(validate_character_literal("xGG", span).is_err());
}
#[test]
fn test_string_unescaping() {
assert_eq!(unescape_string("hello world").unwrap(), "hello world");
assert_eq!(unescape_string(r#"hello\nworld"#).unwrap(), "hello\nworld");
assert_eq!(unescape_string(r#"quote: \""#).unwrap(), r#"quote: ""#);
assert_eq!(unescape_string(r#"\x41;"#).unwrap(), "A");
assert_eq!(unescape_string(r#"\101"#).unwrap(), "A");
// Invalid escape sequences should error
assert!(unescape_string(r#"\z"#).is_err());
}
#[test]
fn test_character_parsing() {
assert_eq!(parse_character_literal("a").unwrap(), 'a');
assert_eq!(parse_character_literal("space").unwrap(), ' ');
assert_eq!(parse_character_literal("newline").unwrap(), '\n');
assert_eq!(parse_character_literal("x41").unwrap(), 'A');
assert_eq!(parse_character_literal("x1F600").unwrap(), '😀');
// Invalid literals should error
assert!(parse_character_literal("").is_err());
assert!(parse_character_literal("ab").is_err());
}
#[test]
fn test_unicode_validation() {
let span = Span::new(0, 10);
// Valid Unicode
assert!(validate_string_escapes(r#"\x1F600;"#, span).is_ok()); // Emoji
assert!(validate_character_literal("x1F600", span).is_ok());
// Invalid Unicode (too large)
assert!(validate_string_escapes(r#"\x110000;"#, span).is_err());
assert!(validate_character_literal("x110000", span).is_err());
// Surrogate pairs (invalid)
assert!(validate_string_escapes(r#"\xD800;"#, span).is_err());
assert!(validate_character_literal("xD800", span).is_err());
}
}