Crate gobble

Gobble is a simple parser combinator system for parsing strings that aims to leave your parser looking as much like a declarative grammar as possible while still being rust code

Creating Parsers in rust should be quite straight forward. For example parsing a function call

use gobble::*;
parser!{
    (Ident->String)
    string((Alpha.one(),(Alpha,NumDigit,'_').istar()))
}

parser!{
    (FSig->(String,Vec<String>))
    (first(Ident,"("),sep_until_ig(Ident,",",")"))
}
let (nm, args) = FSig.parse_s("loadFile1(fname,ref)").unwrap();
assert_eq!(nm, "loadFile1");
assert_eq!(args, vec!["fname", "ref"]);
//Idents can't begin with numbers
assert!(FSig.parse_s("23file(fname,ref)").is_err());

If you’d prefer not to use macros, you don’t have to:

use gobble::*;
let ident = || string((Alpha.one(),(Alpha,NumDigit,'_').istar()));

let fsig = (first(ident(),"("),sep_until_ig(ident(),",",")"));
  
 let (nm, args) = fsig.parse_s("loadFile1(fname,ref)").unwrap();
 assert_eq!(nm, "loadFile1");
 assert_eq!(args, vec!["fname", "ref"]);
 //identifiers cant start with numbers,
 assert!(fsig.parse_s("23file(fname,ref)").is_err());
  

But the macros guarantee of Zero-Sized types which is nice when combining them

To work this library depends the following:

pub enum ParseError {
   //...
}

// In the OK Case the value mean
//   LCChars = copy of original, but moved forward,
//   V = The resulting type
//   Option<ParserError> Only "Some" if the parser could have contined with more data
//   --This is useful for tracking what values would have been expected at a certain point
//
pub type ParseRes<'a, V> = Result<(LCChars<'a>, V,Option<ParseError>), ParseError>;

//implements Iterator and can be cloned relatively cheaply
pub struct LCChars<'a>{
   it:std::str::Chars<'a>,
   line:usize,
   col:usize,
}

pub trait Parser<V> {
   // Takes a non-mut pointer to the iterator, so that the caller
   // may try something else if this doesn't work
   // clone it before reading next
   fn parse<'a>(&self,it:&LCChars<'a>)->ParseRes<'a,V>;
    
   //...helper methods
}
pub trait CharBool {
   fn char_bool(&self,c:char)->bool;
   //....helper methods
   //
}

Parser is automatically implemented for:

• Fn<'a>(&LCChars<'a>)->ParseRes<'a,String>
• &'static str which will return itself if it matches
• char which will return itself if it matched the next char
• Tuples of up to 6 parsers. Returning a tuple of all the parsers matched one after the other.

Most of the time a parser can be built simply by combining other parsers

use gobble::*;

// map can be used to convert one result to another
// keyval is now a function that returns a parser
let keyval = || (common::Ident,":",common::Quoted).map(|(a,_,c)|(a,c));

//this can also be written as below for better type safety
fn keyval2()->impl Parser<Out=(String,String)>{
   (common::Ident,":",common::Quoted).map(|(a,_,c)|(a,c))
}

// or as a macro KeyVal is now a struct like:
// pub struct KeyVal;
parser!{
   (KeyVal->(String,String))
   (common::Ident,":",common::Quoted).map(|(a,_,c)|(a,c))
}
 
//parse_s is a helper on Parsers
let (k,v) = keyval().parse_s(r#"car:"mini""#).unwrap();
assert_eq!(k,"car");
assert_eq!(v,"mini");

//this can now be combined with other parsers.
// 'ig_then' combines 2 parsers and drops the result of the first
// 'then_ig' drops the result of the second
// 'sep_until will repeat the first term into a Vec, separated by the second
//    until the final term.
let obj = || "{".ig_then(sep_until_ig(keyval(),",","}"));

let obs = obj().parse_s(r#"{cat:"Tiddles",dog:"Spot"}"#).unwrap();
assert_eq!(obs[0],("cat".to_string(),"Tiddles".to_string()));

CharBool

CharBool is the trait for boolean char checks. It is auto implemented for:

• Fn(char)->bool
• char – Returns true if the input matches the char
• &’static str – returns true if the str contains the input
• several zero size types - Alpha,NumDigit,HexDigit,WS,WSL,Any
• Tuples of up to 6 CharBools – returning true if any of the members succeed

This means you can combine them in tuples (Alpha,NumDigit,"_").char_bool(c) will be true if any of them match

CharBool also provides several helper methods which each return a parser

• one(self) matches and returns exactly 1 character
• plus(self) ‘+’ requires at least 1 matches and ruturns a string
• min_n(self,n:usize) requires at least n matches and ruturns a string
• star(self) ‘*’ matches any number of chars returning a string
• exact(self,n:usize) ‘*’ matches exactly n chars returning a string
• iplus(self) ‘+’ requires at least 1 matches and ruturns a ()
• istar(self) ‘*’ matches any number of chars returning a ()
• iexact(self,n:usize) matches exactly n chars returning a ()

And a helper that returns a CharBool

• except(self,cb:CharBool) Passes if self does, and cb doesnt

use gobble::*;
let s = |c| c > 'w' || c == 'z';
let xv = s.one().parse_s("xhello").unwrap();
assert_eq!(xv,'x');

let id = (Alpha,"_*").min_n(4).parse_s("sm*shing_game+you").unwrap();
assert_eq!(id,"sm*shing_game");

// not enough matches
assert!((NumDigit,"abc").min_n(4).parse_s("23fflr").is_err());

// any succeeds even with no matches equivilent to min_n(0) but "Zero Size"
assert_eq!((NumDigit,"abc").star().parse_s("23fflr"),Ok("23".to_string()));
assert_eq!((NumDigit,"abc").star().parse_s("fflr"),Ok("".to_string()));

White Space

White space is pretty straight forward to handle

use gobble::*;
let my_ws = || " \t".star();
// middle takes three parsers and returns the result of the middle
// this could also be done easily with 'map' or 'then_ig'
let my_s = |p| middle(my_ws(),p,my_ws());

let sp_id = my_s(common::Ident);
let v = sp_id.parse_s("   \t  doggo  ").unwrap();
assert_eq!(v,"doggo");

That said gobble already provides WS and s_(p)

use gobble::*;
//eoi = end of input
let p = repeat_until_ig(s_("abc".plus()),eoi);
let r = p.parse_s("aaa \tbbb bab").unwrap();
assert_eq!(r,vec!["aaa","bbb","bab"]);

Recursive Structures

Some structures like Json, or programming languages need to be able to handle recursion. Simply combining the function parsers could lead to infinitely sized structures.

The simplest way to avoid this problem is to use the parser macro. Every parser created with the macro is zero sized

But if you would really rather not use the macros, the way to handle this is to make sure one member of the loop is not builtd into the structure. Instead to create it using the ‘Fn ->ParseRes’ method.

use gobble::*;
#[derive(Debug,PartialEq)]
enum Expr {
    Val(isize),
    Add(Box<Expr>,Box<Expr>),
    Paren(Box<Expr>),
}

fn expr_l()->impl Parser<Out=Expr>{
    or(
        middle("(",s_(expr),")").map(|e|Expr::Paren(Box::new(e))),
        common::Int.map(|v|Expr::Val(v))
    )
}

// using the full fn def we avoid the recursive structure
fn expr<'a>(it:&LCChars<'a>)->ParseRes<'a,Expr> {
    //note that expr_l has brackets but expr doesnt.
    //expr is a reference to a static function
    let p = (expr_l(),maybe(s_("+").ig_then(expr)))
        .map(|(l,opr)|match opr{
            Some(r)=>Expr::Add(Box::new(l),Box::new(r)),
            None=>l,
        });
     

    p.parse(it)
}

let r = expr.parse_s("45 + (34+3 )").unwrap();

//recursive structures are never fun to write manually
assert_eq!(r,Expr::Add(
                Box::new(Expr::Val(45)),
                Box::new(Expr::Paren(Box::new(Expr::Add(
                    Box::new(Expr::Val(34)),
                    Box::new(Expr::Val(3))
                ))))
            ));

Re-exports

pub use chars::*;

pub use combi::*;

pub use err::*;

pub use iter::*;

pub use macros::*;

pub use ptrait::*;

pub use reader::*;

pub use repeater::*;

pub use skip::*;

pub use strings::*;

pub use tuple::*;

Modules

chars

CharBool is the main trait for checking if a character is in a set. There are several helper methods to turn these into Parsers such as

combi

common

Generally useful base parsers Str,Int,Uint,Esc,Float

err

iter

macros

The macros primarily exist to make creating zero size parsers easier. Without putting them in macros “&’static str” and “chars” can act as parsers, but they have a size, and when combined they can become bigger. If however all the parsers you combine have zero size, then the final resulting parser will also be zero size and therefor much easier to construct

ptrait

pull

reader

repeater

skip

strings

traits

This Is a prelude tye module for using Gobble If the parser is written in another module and you only need access to the traits that make it work use gobble::traits::*;

tuple

Macros

as_id

char_bool

char_bools

enum_parser

or

a macro replacement for numbered or statements.

or_ig

parser

Makes zero sized parsers based on the expression given and potentially the return type given.

parser_as