Need to specify generics for every function

[Houdiee]

okay so im just trying to get something very basic up and running

use chumsky::{Parser, error::Rich, extra, prelude::*};

use crate::token::{Keyword, Literal, Token, TokenKind};

pub type LexerInput<'src> = &'src str;
pub type LexerOutput<'src> = Vec<Token<'src>>;

pub fn lexer<'src>() -> impl Parser<'src, LexerInput<'src>, LexerOutput<'src>, extra::Err<Rich<'src, char>>> {
    let ident = text::ident().map(TokenKind::Identifier);

    todo()
}

but no matter which prelude function i use i always get the same error:

error[E0284]: type annotations needed
 --> src/lexer.rs:9:17
  |
9 |     let ident = text::ident().map(TokenKind::Identifier);
  |                 ^^^^^^^^^^^ cannot infer type of the type parameter `I` declared on the function `ident`
  |
  = note: cannot satisfy `<_ as chumsky::input::Input<'_>>::Token == _`
help: consider specifying the generic arguments
  |
9 |     let ident = text::ident::<I, E>().map(TokenKind::Identifier);
  |                            ++++++++

but looking at the docs and the examples, specifying the generics shouldn't be required. How do i fix this? help is appreciated!

[Zij-IT]

Welcome to chumsky!

The reason that the error happens is similar to why in the following code, you'd have to specify a type for Vec.

fn into_vec<T: Clone>(t: T) -> Vec<T> {
    let ret: Vec<_> = vec![];
    todo!("push add t to `ret`")
}

In this case, the simplest solution is to give the partial result for token:

pub fn lexer<'src>() -> impl Parser<'src, LexerInput<'src>, LexerOutput<'src>, extra::Err<Rich<'src, char>>> {
    let ident = text::ident().map(TokenKind::Identifier);

    chumsky::prelude::choice((ident,))
}

If you'd want to maintain todo behavior, you could add chumsky::prelude::todo() as the first parser in the choice, so that if it tries to parse anything it will explode.

[Houdiee]

i see, that makes sense, thanks very much