From a76cd56b9f8cce132555f6c3b59d76da5ae86f6b Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Tue, 30 Mar 2021 16:51:51 +0530
Subject: add new catch-all error types

---
 src/lisp/parse.rs | 46 ++++++++++++++++++++++++++--------------------
 1 file changed, 26 insertions(+), 20 deletions(-)

(limited to 'src/lisp/parse.rs')

diff --git a/src/lisp/parse.rs b/src/lisp/parse.rs
index 6a8de9f..737e7ad 100644
--- a/src/lisp/parse.rs
+++ b/src/lisp/parse.rs
@@ -25,22 +25,28 @@ impl<'lex> Parser<'lex> {
         }
     }
 
-    pub fn parse_expr(&mut self) -> Result<LispExpr, LispError> {
+    pub fn parse_expr(&mut self) -> Result<LispExpr, ParseError> {
         let mut stack = Vec::new();
         let mut total_backticks = 0;
         loop {
             let (span, token) = self.next()?;
-            let r: Result<LispExpr, LispError> = match token {
+            let r: Result<LispExpr, ParseError> = match token {
                 Token::LeftParen => {
                     stack.push(Group::Parens(Vec::new()));
                     continue;
                 }
                 Token::RightParen => {
-                    let group = stack.pop().ok_or_else(
-                        || (ParseError::new(span, ParseErrorKind::UnmatchedParen)), // unmatched paren here
-                    )?;
+                    let group = stack
+                        .pop()
+                        .ok_or_else(|| (ParseError::new(span, ParseErrorKind::UnmatchedParen)))?;
                     match group {
-                        Group::Parens(v) => Ok(LispExpr::List(v)),
+                        Group::Parens(v) => {
+                            if v.len() == 0 {
+                                Ok(LispExpr::Unit)
+                            } else {
+                                Ok(LispExpr::List(v))
+                            }
+                        }
                         _ => Err(From::from(ParseError::new(
                             span,
                             ParseErrorKind::UnexpectedToken {
@@ -59,11 +65,11 @@ impl<'lex> Parser<'lex> {
                     .map(|n| LispExpr::Number(LispNumber::Integer(n)))
                     .map_err(|_| ParseError::new(span, ParseErrorKind::LiteralParseError).into()),
                 Token::String(s) => Ok(LispExpr::StringLit(s[1..s.len() - 1].into())),
-                Token::Char(s) => Ok(LispExpr::Char(s.chars().nth(2).ok_or_else(
-                    || -> LispError {
-                        ParseError::new(span, ParseErrorKind::LiteralParseError).into()
-                    },
-                )?)),
+                Token::Char(s) => {
+                    Ok(LispExpr::Char(s.chars().nth(2).ok_or_else(|| {
+                        ParseError::new(span, ParseErrorKind::LiteralParseError)
+                    })?))
+                }
                 Token::Name(n) => Ok(name_expr(n)),
                 Token::BackQuote => {
                     total_backticks += 1;
@@ -76,7 +82,7 @@ impl<'lex> Parser<'lex> {
                 }
                 Token::Comma => {
                     if total_backticks <= 0 {
-                        return Err(ParseError::new(span, ParseErrorKind::UnbalancedComma).into());
+                        return Err(ParseError::new(span, ParseErrorKind::UnbalancedComma));
                     }
                     total_backticks -= 1;
                     if let Some(&mut Group::Backticks(ref mut n)) = stack.last_mut() {
@@ -88,7 +94,7 @@ impl<'lex> Parser<'lex> {
                 }
                 Token::CommaAt => {
                     if total_backticks <= 0 {
-                        return Err(ParseError::new(span, ParseErrorKind::UnbalancedComma).into());
+                        return Err(ParseError::new(span, ParseErrorKind::UnbalancedComma));
                     }
                     total_backticks -= 1;
                     stack.push(Group::CommaAt);
@@ -109,9 +115,9 @@ impl<'lex> Parser<'lex> {
                     });
 
                     if any_paren {
-                        Err(ParseError::new(span, ParseErrorKind::MissingCloseParen).into())
+                        Err(ParseError::new(span, ParseErrorKind::MissingCloseParen))
                     } else {
-                        Err(ParseError::new(span, ParseErrorKind::UnexpectedEof).into())
+                        Err(ParseError::new(span, ParseErrorKind::UnexpectedEof))
                     }
                 }
             };
@@ -148,13 +154,13 @@ impl<'lex> Parser<'lex> {
         }
     }
 
-    fn next(&mut self) -> Result<(Span, Token<'lex>), LispError> {
+    fn next(&mut self) -> Result<(Span, Token<'lex>), ParseError> {
         let r = self.peek()?;
         self.cur_token = None;
         Ok(r)
     }
 
-    fn peek(&mut self) -> Result<(Span, Token<'lex>), LispError> {
+    fn peek(&mut self) -> Result<(Span, Token<'lex>), ParseError> {
         if let Some(tok) = self.cur_token {
             Ok(tok)
         } else {
@@ -164,7 +170,7 @@ impl<'lex> Parser<'lex> {
         }
     }
 
-    pub fn parse_single_expr(&mut self) -> Result<LispExpr, LispError> {
+    pub fn parse_single_expr(&mut self) -> Result<LispExpr, ParseError> {
         let expr = self.parse_expr()?;
 
         match self.next()? {
@@ -180,7 +186,7 @@ impl<'lex> Parser<'lex> {
         }
     }
 
-    pub fn parse_exprs(&mut self) -> Result<Vec<LispExpr>, LispError> {
+    pub fn parse_exprs(&mut self) -> Result<Vec<LispExpr>, ParseError> {
         let mut res = Vec::new();
         loop {
             match self.peek()? {
@@ -203,7 +209,7 @@ fn name_expr(input: &str) -> LispExpr {
 #[cfg(test)]
 mod tests {
     use super::*;
-    fn parse(input: &str) -> Result<LispExpr, LispError> {
+    fn parse(input: &str) -> Result<LispExpr, ParseError> {
         let mut parser = Parser::new(Lexer::new(input, 0));
 
         parser.parse_single_expr()
-- 
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