From e362e83b996f9ba914c88630bec28b703c535dcc Mon Sep 17 00:00:00 2001
From: Greg Brown <gmb60@cam.ac.uk>
Date: Thu, 19 Nov 2020 13:57:14 +0000
Subject: Switch parsing core to syn

---
 src/nibble/mod.rs        | 926 +++++++----------------------------------------
 src/nibble/parse/iter.rs | 149 --------
 src/nibble/parse/mod.rs  |  61 ----
 3 files changed, 136 insertions(+), 1000 deletions(-)
 delete mode 100644 src/nibble/parse/iter.rs
 delete mode 100644 src/nibble/parse/mod.rs

(limited to 'src')

diff --git a/src/nibble/mod.rs b/src/nibble/mod.rs
index 5b51049..478e0cf 100644
--- a/src/nibble/mod.rs
+++ b/src/nibble/mod.rs
@@ -4,183 +4,85 @@ use crate::ast::{
     self,
     convert::{Context, Convert},
 };
-
-use self::parse::{
-    iter::{Peek, PeekExt, PeekableTakeWhile},
-    requires, Parse, ParseError,
+use syn::ext::IdentExt;
+use syn::punctuated::Punctuated;
+use syn::{
+    parse::{Parse, ParseStream},
+    token, Result,
 };
-use std::convert::Infallible;
-use std::str::FromStr;
 
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub struct Ident {
-    name: String,
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct Epsilon {
+    paren_tok: token::Paren,
 }
 
-impl Parse for Ident {
-    type Err = Infallible;
-
-    fn parse<I: Peek<Item = char>>(mut iter: I) -> Result<Self, ParseError<Self::Err>> {
-        // rustc can't predict type, but rust-analyzer can...
-        let name: String = PeekableTakeWhile::new(&mut iter, |c| c.is_alphabetic()).collect();
-        if name.is_empty() {
-            if let Some(c) = iter.peek() {
-                Err(ParseError::InvalidCharacter(*c))
-            } else {
-                Err(ParseError::EndOfFile)
-            }
+impl Parse for Epsilon {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let content;
+        let paren_tok = syn::parenthesized!(content in input);
+        if content.is_empty() {
+            Ok(Self { paren_tok })
         } else {
-            Ok(Self { name })
+            Err(content.error("expected empty parentheses"))
         }
     }
 }
 
-impl FromStr for Ident {
-    type Err = ParseError<<Ident as Parse>::Err>;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Ident::parse(s.chars().peekable())
+impl Convert for Epsilon {
+    fn convert(self, _: &Context) -> ast::Term {
+        ast::Term::Epsilon
     }
 }
 
+type Ident = syn::Ident;
+
 impl Convert for Ident {
     fn convert(self, context: &Context) -> ast::Term {
         use ast::Term;
+        let name = self.to_string();
 
-        if let Some(variable) = context.get(&self.name) {
+        if let Some(variable) = context.get(&name) {
             Term::Variable(variable)
         } else {
-            Term::Call(self.name, vec![])
+            Term::Call(name, vec![])
         }
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub struct Literal {
-    contents: String,
-}
-
-impl Parse for Literal {
-    type Err = LiteralError;
-
-    fn parse<I: Peek<Item = char>>(mut iter: I) -> Result<Self, ParseError<Self::Err>> {
-        fn parse_digit<I: Peek<Item = char>>(
-            mut iter: I,
-            radix: u32,
-        ) -> Result<u32, ParseError<LiteralError>> {
-            Ok(iter
-                .next_if(|c| c.is_digit(radix))
-                .ok_or(ParseError::EndOfFile)?
-                .map_err(|i| ParseError::InvalidCharacter(*i.peek().unwrap()))?
-                .to_digit(radix)
-                .unwrap())
-        }
-
-        /// Parse full character escape.
-        fn parse_escape<I: Peek<Item = char>>(
-            mut iter: I,
-        ) -> Result<char, ParseError<LiteralError>> {
-            requires(&mut iter, '\\')?;
-            match iter.peek().ok_or(ParseError::EndOfFile)? {
-                '\'' | '\"' | '\\' => Ok(iter.next().unwrap()),
-                'n' => {
-                    requires(iter, 'n')?;
-                    Ok('\n')
-                }
-                'r' => {
-                    requires(iter, 'r')?;
-                    Ok('\r')
-                }
-                't' => {
-                    requires(iter, 't')?;
-                    Ok('\t')
-                }
-                '0' => {
-                    requires(iter, '0')?;
-                    Ok('\0')
-                }
-                'x' => {
-                    requires(&mut iter, 'x')?;
-                    let upper = parse_digit(&mut iter, 8)?;
-                    let ord = 16 * upper + parse_digit(&mut iter, 16)?;
-                    std::char::from_u32(ord)
-                        .ok_or(ParseError::Other(LiteralError::InvalidCharacterCode(ord)))
-                }
-                'u' => {
-                    requires(&mut iter, 'u')?;
-                    requires(&mut iter, '{')?;
-                    let mut ord = 0;
-                    for _ in 1..=6 {
-                        ord *= 16;
-                        ord += parse_digit(&mut iter, 16)?;
-                        iter.advance_while(|&c| c == '_');
-
-                        if iter.peek() == Some(&'}') {
-                            break;
-                        }
-                    }
-                    requires(&mut iter, '}')?;
-
-                    std::char::from_u32(ord)
-                        .ok_or(ParseError::Other(LiteralError::InvalidCharacterCode(ord)))
-                }
-                &c => Err(ParseError::InvalidCharacter(c)),
-            }
-        }
-
-        requires(&mut iter, '\'')?;
-
-        let mut s = String::new();
-
-        loop {
-            match iter.peek().ok_or(ParseError::EndOfFile)? {
-                '\'' => {
-                    iter.next();
-                    return if s.is_empty() {
-                        Err(ParseError::Other(LiteralError::EmptyLiteral))
-                    } else {
-                        Ok(Literal { contents: s })
-                    };
-                }
-                &c @ '\n' | &c @ '\r' | &c @ '\t' => return Err(ParseError::InvalidCharacter(c)),
-                '\\' => s.push(parse_escape(&mut iter)?),
-                _ => s.push(iter.next().unwrap()),
-            }
-        }
-    }
-}
+type Literal = syn::LitStr;
 
 impl Convert for Literal {
     fn convert(self, _context: &Context) -> ast::Term {
-        ast::Term::Literal(self.contents)
+        ast::Term::Literal(self.value())
     }
 }
 
-impl FromStr for Literal {
-    type Err = ParseError<<Literal as Parse>::Err>;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Literal::parse(s.chars().peekable())
-    }
-}
-
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-pub enum LiteralError {
-    EmptyLiteral,
-    InvalidCharacterCode(u32),
-}
-
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Call {
     name: Ident,
-    args: Vec<Expression>,
+    paren_tok: token::Paren,
+    args: Punctuated<Expression, syn::Token![,]>,
+}
+
+impl Parse for Call {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let args;
+        let name = input.call(Ident::parse_any)?;
+        let paren_tok = syn::parenthesized!(args in input);
+        let args = args.call(Punctuated::parse_terminated)?;
+        Ok(Self {
+            name,
+            paren_tok,
+            args,
+        })
+    }
 }
 
 impl Convert for Call {
     fn convert(self, context: &Context) -> ast::Term {
         use ast::Term;
         Term::Call(
-            self.name.name,
+            self.name.to_string(),
             self.args.into_iter().map(|e| e.convert(context)).collect(),
         )
     }
@@ -188,31 +90,27 @@ impl Convert for Call {
 
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Fix {
+    bracket_token: token::Bracket,
     arg: Ident,
+    paren_token: token::Paren,
     expr: Expression,
 }
 
 impl Parse for Fix {
-    type Err = FixError;
-
-    fn parse<I: Peek<Item = char>>(mut iter: I) -> Result<Self, ParseError<Self::Err>> {
-        requires(&mut iter, '[')?;
-        let arg = Ident::parse(&mut iter).map_err(ParseError::map)?;
-        requires(&mut iter, ']')?;
-        requires(&mut iter, '(')?;
-        iter.advance_while(|c| c.is_whitespace());
-        let expr = Expression::parse(Box::new(&mut iter as &mut dyn Peek<Item = char>))
-            .map_err(ParseError::map)?;
-        requires(&mut iter, ')')?;
-        Ok(Self { arg, expr })
-    }
-}
-
-impl FromStr for Fix {
-    type Err = ParseError<<Fix as Parse>::Err>;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Fix::parse(s.chars().peekable())
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let arg;
+        let bracket_token = syn::bracketed!(arg in input);
+        let arg = arg.call(Ident::parse_any)?;
+
+        let expr;
+        let paren_token = syn::parenthesized!(expr in input);
+        let expr = expr.parse()?;
+        Ok(Self {
+            bracket_token,
+            arg,
+            paren_token,
+            expr,
+        })
     }
 }
 
@@ -220,97 +118,86 @@ impl Convert for Fix {
     fn convert(self, context: &Context) -> ast::Term {
         use ast::Term;
         let expr = self.expr;
-        Term::Fix(Box::new(context.push(self.arg.name, |c| expr.convert(c))))
+        Term::Fix(Box::new(
+            context.push(self.arg.to_string(), |c| expr.convert(c)),
+        ))
     }
 }
 
 #[derive(Clone, Debug, Eq, PartialEq)]
-pub struct FixError(Box<ExpressionError>);
+pub struct ParenExpression {
+    paren_tok: token::Paren,
+    expr: Expression,
+}
 
-impl From<Infallible> for FixError {
-    fn from(other: Infallible) -> Self {
-        match other {}
+impl Parse for ParenExpression {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let expr;
+        let paren_tok = syn::parenthesized!(expr in input);
+        let expr = expr.parse()?;
+        Ok(Self { paren_tok, expr })
     }
 }
 
-impl From<ExpressionError> for FixError {
-    fn from(other: ExpressionError) -> Self {
-        Self(Box::new(other))
+impl Convert for ParenExpression {
+    fn convert(self, context: &Context) -> ast::Term {
+        self.expr.convert(context)
     }
 }
 
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum Term {
-    Epsilon,
+    Epsilon(Epsilon),
     Ident(Ident),
     Literal(Literal),
     Call(Call),
     Fix(Fix),
-    Parens(Expression),
+    Parens(ParenExpression),
 }
 
 impl Parse for Term {
-    type Err = TermError;
-
-    fn parse<I: Peek<Item = char>>(mut iter: I) -> Result<Self, ParseError<Self::Err>> {
-        match iter.peek().ok_or(ParseError::EndOfFile)? {
-            '(' => {
-                iter.next();
-
-                if iter.consume_if_next(&')') {
-                    Ok(Self::Epsilon)
-                } else {
-                    let expr = Expression::parse(Box::new(&mut iter as &mut dyn Peek<Item = char>))
-                        .map_err(ParseError::map)?;
-                    requires(iter, ')').map(|_| Self::Parens(expr))
-                }
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let lookahead = input.lookahead1();
+        if lookahead.peek(token::Paren) {
+            let content;
+            let paren_tok = syn::parenthesized!(content in input);
+            if content.is_empty() {
+                Ok(Self::Epsilon(Epsilon { paren_tok }))
+            } else {
+                content
+                    .parse()
+                    .map(|expr| Self::Parens(ParenExpression { paren_tok, expr }))
             }
-            '[' => Fix::parse(iter).map(Self::Fix).map_err(ParseError::map),
-            '\'' => Literal::parse(iter)
-                .map(Self::Literal)
-                .map_err(ParseError::map),
-            c if c.is_alphabetic() => {
-                let ident = Ident::parse(&mut iter).map_err(ParseError::map)?;
-
-                if iter.consume_if_next(&'(') {
-                    iter.advance_while(|c| c.is_whitespace());
-                    let mut args = Vec::new();
-                    loop {
-                        args.push(
-                            Expression::parse(Box::new(&mut iter as &mut dyn Peek<Item = char>))
-                                .map_err(ParseError::<CallError>::map)
-                                .map_err(ParseError::map)?,
-                        );
-
-                        if iter.consume_if_next(&')') {
-                            return Ok(Self::Call(Call { name: ident, args }));
-                        }
-
-                        requires(&mut iter, ',')?;
-                        iter.advance_while(|c| c.is_whitespace());
-                    }
-                } else {
-                    Ok(Self::Ident(ident))
-                }
+        } else if lookahead.peek(Ident::peek_any) {
+            let name = input.call(Ident::parse_any)?;
+            if input.peek(token::Paren) {
+                let args;
+                let paren_tok = syn::parenthesized!(args in input);
+                args.call(Punctuated::parse_terminated).map(|args| {
+                    Self::Call(Call {
+                        name,
+                        paren_tok,
+                        args,
+                    })
+                })
+            } else {
+                Ok(Self::Ident(name))
             }
-            &c => Err(ParseError::InvalidCharacter(c)),
+        } else if lookahead.peek(token::Bracket) {
+            input.parse().map(Self::Fix)
+        } else if lookahead.peek(syn::LitStr) {
+            input.parse().map(Self::Literal)
+        } else {
+            Err(lookahead.error())
         }
     }
 }
 
-impl FromStr for Term {
-    type Err = ParseError<<Term as Parse>::Err>;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Term::parse(s.chars().peekable())
-    }
-}
-
 impl Convert for Term {
     fn convert(self, context: &Context) -> ast::Term {
         use ast::Term;
         match self {
-            Self::Epsilon => Term::Epsilon,
+            Self::Epsilon(_) => Term::Epsilon,
             Self::Ident(i) => i.convert(context),
             Self::Literal(l) => l.convert(context),
             Self::Call(c) => c.convert(context),
@@ -320,81 +207,16 @@ impl Convert for Term {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub struct CallError(Box<ExpressionError>);
-
-impl From<ExpressionError> for CallError {
-    fn from(other: ExpressionError) -> Self {
-        Self(Box::new(other))
-    }
-}
-
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub enum TermError {
-    Literal(LiteralError),
-    Call(CallError),
-    Fix(FixError),
-    Parens(Box<ExpressionError>),
-}
-
-impl From<Infallible> for TermError {
-    fn from(other: Infallible) -> Self {
-        match other {}
-    }
-}
-
-impl From<ExpressionError> for TermError {
-    fn from(other: ExpressionError) -> Self {
-        Self::Parens(Box::new(other))
-    }
-}
-
-impl From<FixError> for TermError {
-    fn from(other: FixError) -> Self {
-        Self::Fix(other)
-    }
-}
-
-impl From<CallError> for TermError {
-    fn from(other: CallError) -> Self {
-        Self::Call(other)
-    }
-}
-
-impl From<LiteralError> for TermError {
-    fn from(other: LiteralError) -> Self {
-        Self::Literal(other)
-    }
-}
-
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Cat {
-    terms: Vec<Term>,
+    terms: Punctuated<Term, syn::Token![.]>,
 }
 
 impl Parse for Cat {
-    type Err = SeqError;
-
-    fn parse<I: Peek<Item = char>>(mut iter: I) -> Result<Self, ParseError<Self::Err>> {
-        let mut terms = Vec::new();
-        terms.push(Term::parse(&mut iter).map_err(ParseError::map)?);
-        iter.advance_while(|c| c.is_whitespace());
-
-        while iter.consume_if_next(&'.') {
-            iter.advance_while(|c| c.is_whitespace());
-            terms.push(Term::parse(&mut iter).map_err(ParseError::map)?);
-            iter.advance_while(|c| c.is_whitespace());
-        }
-
-        Ok(Self { terms })
-    }
-}
-
-impl FromStr for Cat {
-    type Err = ParseError<<Cat as Parse>::Err>;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Cat::parse(s.chars().peekable())
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        Ok(Self {
+            terms: input.call(Punctuated::parse_separated_nonempty)?,
+        })
     }
 }
 
@@ -407,41 +229,16 @@ impl Convert for Cat {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub struct SeqError(TermError);
-
-impl From<TermError> for SeqError {
-    fn from(other: TermError) -> Self {
-        Self(other)
-    }
-}
-
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Alt {
-    cats: Vec<Cat>,
+    cats: Punctuated<Cat, syn::Token![|]>,
 }
 
 impl Parse for Alt {
-    type Err = AltError;
-
-    fn parse<I: Peek<Item = char>>(mut iter: I) -> Result<Self, ParseError<Self::Err>> {
-        let mut seqs = Vec::new();
-        seqs.push(Cat::parse(&mut iter).map_err(ParseError::map)?);
-
-        while iter.consume_if_next(&'|') {
-            iter.advance_while(|c| c.is_whitespace());
-            seqs.push(Cat::parse(&mut iter).map_err(ParseError::map)?);
-        }
-
-        Ok(Self { cats: seqs })
-    }
-}
-
-impl FromStr for Alt {
-    type Err = ParseError<<Alt as Parse>::Err>;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Alt::parse(s.chars().peekable())
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        Ok(Self {
+            cats: input.call(Punctuated::parse_separated_nonempty)?,
+        })
     }
 }
 
@@ -454,485 +251,34 @@ impl Convert for Alt {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub struct AltError(SeqError);
-
-impl From<SeqError> for AltError {
-    fn from(other: SeqError) -> Self {
-        Self(other)
-    }
-}
-
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub struct Expression {
-    alt: Alt,
-}
-
-impl Parse for Expression {
-    type Err = ExpressionError;
-
-    fn parse<I: Peek<Item = char>>(iter: I) -> Result<Self, ParseError<Self::Err>> {
-        Ok(Self {
-            alt: Alt::parse(iter).map_err(ParseError::map)?,
-        })
-    }
-}
-
-impl FromStr for Expression {
-    type Err = ParseError<<Expression as Parse>::Err>;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Expression::parse(s.chars().peekable())
-    }
-}
-
-impl Convert for Expression {
-    fn convert(self, context: &Context) -> ast::Term {
-        self.alt.convert(context)
-    }
-}
-
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub struct ExpressionError(AltError);
-
-impl From<AltError> for ExpressionError {
-    fn from(other: AltError) -> Self {
-        Self(other)
-    }
-}
+type Expression = Alt;
 
 #[cfg(test)]
 mod tests {
-    use super::{
-        parse::{Parse, ParseError},
-        Alt, Cat, Expression, Fix, Ident, Literal, LiteralError, Term,
-    };
-    use crate::ast::{
-        self,
-        convert::{Context, Convert},
-    };
-    use std::iter;
-
-    macro_rules! parse_indent {
-        ($s:literal) => {
-            assert_eq!(
-                $s.parse(),
-                Ok(Ident {
-                    name: $s.to_owned()
-                })
-            )
-        };
-    }
-
-    #[test]
-    fn parse_ident_simple() {
-        parse_indent!("x");
-        parse_indent!("variable");
-    }
-
-    #[test]
-    fn parse_indent_unicode() {
-        parse_indent!("ℕꥇℜ");
-    }
-
-    #[test]
-    fn parse_indent_stops() {
-        let s = "variable then more text";
-        let mut iter = s.chars().peekable();
-        assert_eq!(
-            Ident::parse(&mut iter),
-            Ok(Ident {
-                name: "variable".to_owned()
-            })
-        );
-        assert_eq!(iter.collect::<String>(), " then more text");
-    }
-
-    #[test]
-    fn parse_indent_not_empty() {
-        assert_eq!("".parse::<Ident>(), Err(ParseError::EndOfFile));
-    }
-
-    #[test]
-    fn parse_indent_alphabetic_only() {
-        assert_eq!(
-            "123".parse::<Ident>(),
-            Err(ParseError::InvalidCharacter('1'))
-        );
-    }
-
-    #[test]
-    fn convert_ident_variable() {
-        use ast::Term;
-        let context = Context::new();
-        context.push("x".to_owned(), |c| {
-            assert_eq!(
-                Ident {
-                    name: "x".to_owned()
-                }
-                .convert(c),
-                Term::Variable(0)
-            );
-
-            c.push("y".to_owned(), |c| {
-                assert_eq!(
-                    Ident {
-                        name: "y".to_owned()
-                    }
-                    .convert(c),
-                    Term::Variable(0)
-                );
-
-                assert_eq!(
-                    Ident {
-                        name: "x".to_owned()
-                    }
-                    .convert(c),
-                    Term::Variable(1)
-                );
-            })
-        })
-    }
-
-    #[test]
-    fn convert_ident_call() {
-        use ast::Term;
-        let context = Context::new();
-
-        assert_eq!(
-            Ident {
-                name: "call".to_owned()
-            }
-            .convert(&context),
-            Term::Call("call".to_owned(), vec![])
-        );
-
-        assert_eq!(
-            Ident {
-                name: "x".to_owned()
-            }
-            .convert(&context),
-            Term::Call("x".to_owned(), vec![])
-        );
-
-        context.push("x".to_owned(), |c| {
-            assert_eq!(
-                Ident {
-                    name: "call".to_owned()
-                }
-                .convert(c),
-                Term::Call("call".to_owned(), vec![])
-            );
-
-            assert_eq!(
-                Ident {
-                    name: "x".to_owned()
-                }
-                .convert(c),
-                Term::Variable(0)
-            );
-        })
-    }
-
-    macro_rules! parse_lit {
-        ($str:literal) => {
-            assert_eq!(
-                Literal::parse(
-                    iter::once('\'')
-                        .chain($str.escape_debug())
-                        .chain(iter::once('\''),)
-                        .peekable()
-                ),
-                Ok(Literal {
-                    contents: $str.to_owned()
-                }),
-            )
-        };
-    }
-
-    #[test]
-    fn parse_literal_basic() {
-        parse_lit!("hello");
-        parse_lit!("this has whitespace");
-    }
+    use syn::parse_str;
+    use super::{Epsilon, Ident, Literal};
 
     #[test]
-    fn parse_literal_quotes() {
-        parse_lit!(r#"quote ' " and backslash \ quoting"#);
+    fn parse_epsilon() {
+        assert!(parse_str::<Epsilon>("()").is_ok());
+        assert!(parse_str::<Epsilon>("(  )").is_ok());
+        assert!(parse_str::<Epsilon>("(").is_err());
+        assert!(parse_str::<Epsilon>(")").is_err());
+        assert!(parse_str::<Epsilon>("(x)").is_err());
     }
 
     #[test]
-    fn parse_literal_ascii_escape() {
-        parse_lit!("newline \n tab \t carriage return \r");
-
-        assert_eq!(
-            r#"'\0'"#.parse(),
-            Ok(Literal {
-                contents: "\0".to_owned()
-            })
-        );
+    fn parse_ident() {
+        assert_eq!(parse_str::<Ident>("x").unwrap().to_string(), "x");
+        assert_eq!(parse_str::<Ident>("x_yz").unwrap().to_string(), "x_yz");
+        assert_eq!(parse_str::<Ident>("a123").unwrap().to_string(), "a123");
+        assert_eq!(parse_str::<Ident>("𝒢𝒢").unwrap().to_string(), "𝒢𝒢");
+        assert!(parse_str::<Ident>("1").is_err());
+        assert!(parse_str::<Ident>("_").is_err());
     }
 
     #[test]
-    fn parse_literal_hex_escape() {
-        assert_eq!(
-            r#"'\x20'"#.parse(),
-            Ok(Literal {
-                contents: " ".to_owned()
-            })
-        );
-    }
-
-    #[test]
-    fn parse_literal_unicode_escape() {
-        parse_lit!("emoji ❤ escape \u{200c}");
-    }
-
-    #[test]
-    fn parse_literal_stops() {
-        let mut iter = "'hi there' Not quoted".chars().peekable();
-        assert_eq!(
-            Literal::parse(&mut iter),
-            Ok(Literal {
-                contents: "hi there".to_owned()
-            })
-        );
-        assert_eq!(iter.collect::<String>(), " Not quoted");
-    }
-
-    #[test]
-    fn parse_literal_needs_quotes() {
-        assert_eq!(
-            "hello".parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('h'))
-        );
-        assert_eq!("'hello".parse::<Literal>(), Err(ParseError::EndOfFile));
-    }
-
-    #[test]
-    fn parse_literal_not_empty() {
-        assert_eq!(
-            "''".parse::<Literal>(),
-            Err(ParseError::Other(LiteralError::EmptyLiteral))
-        );
-    }
-
-    #[test]
-    fn parse_literal_no_forbidden_whitespace() {
-        assert_eq!(
-            "'\n".parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('\n'))
-        );
-        assert_eq!(
-            "'\r".parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('\r'))
-        );
-        assert_eq!(
-            "'\t".parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('\t'))
-        );
-    }
-
-    #[test]
-    fn parse_literal_invalid_escape() {
-        assert_eq!(
-            r#"'\F"#.parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('F'))
-        );
-    }
-
-    #[test]
-    fn parse_literal_bad_hex_escape() {
-        assert_eq!(
-            r#"'\xF"#.parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('F'))
-        );
-        assert_eq!(
-            r#"'\x0z"#.parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('z'))
-        );
-    }
-
-    #[test]
-    fn parse_literal_bad_unicode_escape() {
-        // Negative tests
-        assert_eq!(
-            r#"'\u0"#.parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('0'))
-        );
-        assert_eq!(
-            r#"'\u{}"#.parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('}'))
-        );
-        assert_eq!(
-            r#"'\u{z"#.parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('z'))
-        );
-        assert_eq!(
-            r#"'\u{_"#.parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('_'))
-        );
-        assert_eq!(
-            r#"'\u{0___h"#.parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('h'))
-        );
-        assert_eq!(
-            r#"'\u{D800}"#.parse::<Literal>(),
-            Err(ParseError::Other(LiteralError::InvalidCharacterCode(
-                0xd800
-            )))
-        );
-        assert_eq!(
-            r#"'\u{0000000"#.parse::<Literal>(),
-            Err(ParseError::InvalidCharacter('0'))
-        );
-    }
-
-    #[test]
-    fn convert_literal() {
-        use ast::Term;
-        let context = Context::new();
-        assert_eq!(
-            Literal {
-                contents: "hello".to_owned()
-            }
-            .convert(&context),
-            Term::Literal("hello".to_owned())
-        );
-    }
-
-    #[test]
-    fn parse_fix_basic() {
-        let expr = Expression {
-            alt: Alt {
-                cats: vec![Cat {
-                    terms: vec![Term::Epsilon],
-                }],
-            },
-        };
-        assert_eq!(
-            "[x](())".parse(),
-            Ok(Fix {
-                arg: Ident {
-                    name: "x".to_owned()
-                },
-                expr: expr.clone()
-            })
-        );
-        assert_eq!(
-            "[x](()    )".parse(),
-            Ok(Fix {
-                arg: Ident {
-                    name: "x".to_owned()
-                },
-                expr: expr.clone()
-            })
-        );
-        assert_eq!(
-            "[x](    ())".parse(),
-            Ok(Fix {
-                arg: Ident {
-                    name: "x".to_owned()
-                },
-                expr
-            })
-        );
-    }
-
-    #[test]
-    fn parse_fix_needs_arg() {
-        assert_eq!(
-            "x]()".parse::<Fix>(),
-            Err(ParseError::InvalidCharacter('x'))
-        );
-        assert_eq!(
-            "[]()".parse::<Fix>(),
-            Err(ParseError::InvalidCharacter(']'))
-        );
-    }
-
-    #[test]
-    fn parse_fix_needs_parens() {
-        assert_eq!(
-            "[x]x".parse::<Fix>(),
-            Err(ParseError::InvalidCharacter('x'))
-        );
-        assert_eq!("[x](x".parse::<Fix>(), Err(ParseError::EndOfFile))
-    }
-
-    #[test]
-    fn parse_fix_stops() {
-        let mut iter = "[x](()) Not in fix".chars().peekable();
-        assert_eq!(
-            Fix::parse(&mut iter),
-            Ok(Fix {
-                arg: Ident {
-                    name: "x".to_owned()
-                },
-                expr: Expression {
-                    alt: Alt {
-                        cats: vec![Cat {
-                            terms: vec![Term::Epsilon],
-                        }],
-                    },
-                },
-            })
-        );
-
-        assert_eq!(iter.collect::<String>(), " Not in fix");
-    }
-
-    #[test]
-    fn convert_fix_no_var() {
-        let context = Context::new();
-        let expr = Expression {
-            alt: Alt {
-                cats: vec![Cat {
-                    terms: vec![Term::Epsilon],
-                }],
-            },
-        };
-        assert_eq!(
-            Fix {
-                arg: Ident {
-                    name: "x".to_owned()
-                },
-                expr: expr.clone()
-            }
-            .convert(&context),
-            ast::Term::Fix(Box::new(expr.convert(&context)))
-        )
-    }
-
-    #[test]
-    fn convert_fix_var() {
-        use ast::Term;
-        let context = Context::new();
-        let expr = Expression {
-            alt: Alt {
-                cats: vec![Cat {
-                    terms: vec![super::Term::Ident(Ident {
-                        name: "x".to_owned(),
-                    })],
-                }],
-            },
-        };
-
-        assert_eq!(
-            Fix {
-                arg: Ident {
-                    name: "x".to_owned()
-                },
-                expr
-            }
-            .convert(&context),
-            Term::Fix(Box::new(Term::Alt(
-                Box::new(Term::Cat(
-                    Box::new(Term::Variable(0)),
-                    Box::new(Term::Epsilon)
-                )),
-                Box::new(Term::Bottom)
-            )))
-        )
+    fn parse_literal() {
+        assert_eq!(parse_str::<Literal>(r#""hello""#).unwrap().value(), "hello")
     }
 }
diff --git a/src/nibble/parse/iter.rs b/src/nibble/parse/iter.rs
deleted file mode 100644
index 1c635a3..0000000
--- a/src/nibble/parse/iter.rs
+++ /dev/null
@@ -1,149 +0,0 @@
-use std::iter::Peekable;
-
-pub use self::take_while::PeekableTakeWhile;
-
-/// An iterator with a `peek()` that returns an optional reference to the next
-/// element.
-///
-/// This trait is an extension of the `Peekable` type in the standard library.
-pub trait Peek: Iterator {
-    /// Returns a reference to the [`next`] value without advancing the iterator.
-    ///
-    /// Like [`next`], if there is a value, it is wrapped in [`Some`]. But if
-    /// iteration is over, [`None`] is returned.
-    fn peek(&mut self) -> Option<&Self::Item>;
-}
-
-impl<I: Peek> Peek for &mut I {
-    fn peek(&mut self) -> Option<&Self::Item> {
-        I::peek(self)
-    }
-}
-
-impl<I> Peek for Box<&mut dyn Peek<Item = I>> {
-    fn peek(&mut self) -> Option<&Self::Item> {
-        (**self).peek()
-    }
-}
-
-impl<I: Iterator> Peek for Peekable<I> {
-    fn peek(&mut self) -> Option<&Self::Item> {
-        Peekable::peek(self)
-    }
-}
-
-pub trait PeekExt: Peek {
-    /// Returns the [`next`] value and advance the iterator only if `pred` is true.
-    fn next_if<P: FnOnce(&Self::Item) -> bool>(
-        &mut self,
-        pred: P,
-    ) -> Option<Result<Self::Item, &mut Self>> {
-        let i = self.peek()?;
-
-        if pred(i) {
-            Some(Ok(self.next().unwrap()))
-        } else {
-            Some(Err(self))
-        }
-    }
-
-    fn next_if_then<
-        P: FnOnce(&Self::Item) -> bool,
-        F: FnOnce(Self::Item) -> T,
-        G: FnOnce(&mut Self) -> T,
-        T,
-    >(
-        &mut self,
-        pred: P,
-        matched: F,
-        unmatched: G,
-    ) -> Option<T> {
-        let i = self.peek()?;
-
-        if pred(i) {
-            Some(matched(self.next().unwrap()))
-        } else {
-            Some(unmatched(self))
-        }
-    }
-
-    /// Advances the iterator only if the [`next`] item equals `val`.
-    fn next_if_eq<T>(&mut self, val: &T) -> Option<Result<(), &Self::Item>>
-    where
-        Self::Item: PartialEq<T>,
-    {
-        self.next_if(|i| PartialEq::eq(i, val))
-            .map(|r| r.map(|_| ()).map_err(|i| i.peek().unwrap()))
-    }
-
-    fn consume_if_next<T>(&mut self, val: &T) -> bool
-    where
-        Self::Item: PartialEq<T>,
-    {
-        self.next_if_eq(val).map(|r| r.is_ok()).unwrap_or(false)
-    }
-
-    /// Advance the iterator until `pred` is false, or `peek` returns [`None`].
-    fn advance_while<P: FnMut(&Self::Item) -> bool>(&mut self, mut pred: P) {
-        while self.next_if(&mut pred).map(|r| r.is_ok()).unwrap_or(false) {
-            // Condition already loops for us
-        }
-    }
-}
-
-impl<I: Peek> PeekExt for I {}
-
-mod take_while {
-    use super::Peek;
-
-    #[derive(Clone, Debug, Eq, PartialEq)]
-    pub struct PeekableTakeWhile<I, F> {
-        inner: I,
-        predicate: Option<F>,
-    }
-
-    impl<I, F> PeekableTakeWhile<I, F>
-    where
-        I: Peek,
-        F: FnMut(&<I as Iterator>::Item) -> bool,
-    {
-        pub fn new(iter: I, predicate: F) -> Self {
-            Self {
-                inner: iter,
-                predicate: Some(predicate),
-            }
-        }
-    }
-
-    impl<I, F> Iterator for PeekableTakeWhile<I, F>
-    where
-        I: Peek,
-        F: FnMut(&<I as Iterator>::Item) -> bool,
-    {
-        type Item = <I as Iterator>::Item;
-
-        fn next(&mut self) -> Option<Self::Item> {
-            // Can't inline because of lifetimes
-            let inner = &mut self.inner;
-            if self.predicate.as_mut().and_then(|p| inner.peek().map(p))? {
-                self.inner.next()
-            } else {
-                self.predicate = None;
-                None
-            }
-        }
-    }
-
-    impl<I, F> Peek for PeekableTakeWhile<I, F>
-    where
-        I: Peek,
-        F: FnMut(&<I as Iterator>::Item) -> bool,
-    {
-        fn peek(&mut self) -> Option<&Self::Item> {
-            let inner = &mut self.inner;
-            self.predicate
-                .as_mut()
-                .and_then(move |p| inner.peek().filter(|i| p(i)))
-        }
-    }
-}
diff --git a/src/nibble/parse/mod.rs b/src/nibble/parse/mod.rs
deleted file mode 100644
index 13c4c0e..0000000
--- a/src/nibble/parse/mod.rs
+++ /dev/null
@@ -1,61 +0,0 @@
-pub mod iter;
-
-use self::iter::Peek;
-use self::iter::PeekExt;
-
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-pub enum ParseError<E> {
-    EndOfFile,
-    InvalidCharacter(char),
-    Other(E),
-}
-
-impl<U> ParseError<U> {
-    pub fn map<T: Into<U>>(other: ParseError<T>) -> Self {
-        match other {
-            ParseError::EndOfFile => Self::EndOfFile,
-            ParseError::InvalidCharacter(c) => Self::InvalidCharacter(c),
-            ParseError::Other(t) => Self::Other(t.into())
-        }
-    }
-}
-
-/// Parse a value from an iterator.
-pub trait Parse: Sized {
-    /// The associated error that can be returned from parsing.
-    type Err;
-    /// Parses `iter` to return a value of this type.
-    ///
-    /// This method may not reach the end of `iter`. If so, it must not consume any
-    /// characters in the stream that do not form part of the value.
-    ///
-    /// If parsing succeeds, return the value inside [`Ok`]. Otherwise, when the
-    /// iterator is ill-formatted, return an error specific to the inside [`Err`].
-    /// The error type is specific to the implementation of the trait.
-    fn parse<I: PeekExt<Item = char>>(iter: I) -> Result<Self, ParseError<Self::Err>>;
-}
-
-/// Consumes the next item in `iter` if it equals `c`. Otherwise, returns an
-/// appropriate error without advancing the iterator.
-///
-/// # Examples
-/// Basic usage
-/// ```
-/// use chomp::nibble::parse::{requires, Parse, ParseError};
-/// use std::convert::Infallible;
-///
-/// let s = "hello".to_owned();
-/// let mut iter = s.chars().peekable();
-/// assert_eq!(requires::<_, Infallible>(&mut iter, 'h'), Ok(()));
-/// assert_eq!(requires::<_, Infallible>(&mut iter, 'e'), Ok(()));
-/// assert_eq!(requires::<_, Infallible>(&mut iter, 'z'), Err(ParseError::InvalidCharacter('l')));
-/// assert_eq!(iter.next(), Some('l'));
-/// assert_eq!(iter.next(), Some('l'));
-/// assert_eq!(iter.next(), Some('o'));
-/// assert_eq!(requires::<_, Infallible>(iter, '!'), Err(ParseError::EndOfFile));
-/// ```
-pub fn requires<I: Peek<Item = char>, E>(mut iter: I, c: char) -> Result<(), ParseError<E>> {
-    iter.next_if_eq(&c)
-        .ok_or(ParseError::EndOfFile)?
-        .map_err(|&c| ParseError::InvalidCharacter(c))
-}
-- 
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