[−][src]Crate gobble
Gobble is a simple parser combinator system for parsing strings.
For example parsing a function call
use gobble::*; let ident = || string_2_parts(Alpha.min_n(1),(Alpha,NumDigit,'_').any()); let fsig = (ident().then_ig("("),sep(ident(),",",0).then_ig(")")); 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());
To work this library depends the following:
pub enum ParseError { //... } //The LCChars in the result will be a clone of the incoming iterator //but having iterated to end of the what the parser required. pub type ParseRes<'a, V> = Result<(LCChars<'a>, V), 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 BoolChar { fn bool_char(&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 matcheschar
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_str).map(|(a,_,c)|(a,c)); //this can also be written as below for better type safety fn keyval2()->impl Parser<(String,String)>{ (common_ident,":",common_str).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(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 3 helper methods which each return a parser
one()
matches and returns exactly 1 charactermin_n(n)
requires at least n matches ruturns a stringany()
matches any number of chars returning a string
And a helper that returns a CharBool
except(cb)
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(0) assert_eq!((NumDigit,"abc").any().parse_s("23fflr"),Ok("23".to_string())); assert_eq!((NumDigit,"abc").any().parse_s("fflr"),Ok("".to_string()));
White Space
White space is pretty straight forward to handle
use gobble::*; let my_ws = || " \t".any(); // 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".min_n(1)),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. However with the techniques we have used so far this would lead to infinitely sized structures.
The way to handle this is to make sure one member of the loop is not
build into the structure. Instead to create it using the 'Fn'
use gobble::*; #[derive(Debug,PartialEq)] enum Expr { Val(isize), Add(Box<Expr>,Box<Expr>), Paren(Box<Expr>), } fn expr_l()->impl Parser<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 common::*; |
pub use err::*; |
pub use iter::*; |
pub use ptrait::*; |
pub use reader::*; |
pub use repeater::*; |
pub use skip::*; |
pub use strings::*; |
pub use tuple::*; |
Modules
chars | |
combi | |
common | |
err | |
iter | |
ptrait | |
reader | |
repeater | |
skip | |
strings | |
tuple |