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0.0.8 Jun 22, 2024
0.0.7 Jun 12, 2024
0.0.2 May 30, 2024

#122 in Procedural macros

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Used in unsynn-rust


1.5K SLoC

unsynn (from german 'unsinn' for nonsense) is a minimalist rust parser library. It achives this by leaving out the actual grammar implementations and compromise on simpler error reporting. In exchange it offers simple composeable Parsers and ergonomic Parser construction. Grammars will be implemented in their own crates (see unsynn-rust).

It is primarly intended use is when one wants to create proc macros for rust that define their own grammar or need only sparse rust parsers.


# use unsynn::*;
let mut token_iter = quote::quote!{ foo ( bar, baz, barf ) }.into_iter();

// Composition
let ast =
    Cons::<Ident, ParenthesisGroupContaining::<CommaDelimitedVec<Ident>>>
        ::parse(&mut token_iter).unwrap();

// The same defining a custom type, the macro will generate the `Parser` and `ToToken` impls.
    struct IdentThenParenthesisedIdents {
        ident: Ident,
        pidents: ParenthesisGroupContaining::<CommaDelimitedVec<Ident>>,

let mut token_iter = quote::quote!{ foo ( bar, baz, barf ) }.into_iter();

let ast = IdentThenParenthesisedIdents::parse(&mut token_iter).unwrap();


By defaut unsynn is very lean and does not include extra features. The only thing that are always present are the Parser, Parse and ToTokens traits. The following features enable extra traits:

  • impl_debug
    Adds Debug implementations to generic unsynn types.

  • impl_display
    Adds Display implementations to generic unsynn types.

Note that Display can't be implemented for some std types (eg. Option). Further Display may sometimes be surprising since we do not have rules how to pretty-print tokens (eg. spaces around Delimiters)