DynParser

A small and simple Dynamic Parser

It's not a compile time parser.

You can create and modify the grammar on runtime.

A parser is something that takes an input, process it with some rules and generate an AST

simple_parser

In order to create the grammar, you can build a set of rules, or you can use macros to use a better syntax. But, the easier way, is to use a peg grammar.

Then we need an additional step.

basic_diagram

More info about the peg syntax bellow.

You can also generate rust code from rules generated from peg.

This allow you to avoid the peg step and more...

In fact, in order to use a peg grammar, you have to parse it. How to parse a peg grammar? Well, this is a parser, therefore...

More details about it bellow on section (parsing the parser)

Usage

Add to cargo.toml

[dependencies]
dynparser = "0.1.0"

Watch examples below

Modifications

0.1.0 First version

TODO

Upload version 0.1 to cargo
Document peg module
Move to an isolated module IVector
insert and test EOF

    let peg = r#"
    main    =   "hello" " "  "world"
            /   "hola"
            /   "hola"  " "  "mundo"

        "#,
    ).map_err(|e| {
        println!("{}", e);
        panic!("FAIL");
    })
        .unwrap();

    println!("{:#?}", rules);

    let result = parse("hola mundo", &rules);

Create rules from PEG
- document rules from peg
- calculator parser example
generate code from rules
add errors to grammar
Upload to crates.io
- update usage
- update links to doc
more examples in doc
tail recursion parsing rule
macro for eof
rules path on errors configurable (due to performance)
- check. is it interesting to detail branches on or?

Basic example

Lets create the next grammar:

    main            =   letter letter_or_num+

    letter          =   [a-zA-Z]

    letter_or_num   =   letter
                    /   number

    number          =   [0-9]

This grammar will accept a letter, followed from one or more letters or numbers

Just from peg

basic_diagram

Straightforward...

    extern crate dynparser;
    use dynparser::{parse, rules_from_peg};

    fn main() {
        let rules = rules_from_peg(
            r#"

    main            =   letter letter_or_num+

    letter          =   [a-zA-Z]

    letter_or_num   =   letter
                    /   number

    number          =   [0-9]

            "#,
        ).unwrap();

        assert!(parse("a2AA456bzJ88", &rules).is_ok());
    }

If you want to print more information...

    extern crate dynparser;
    use dynparser::{parse, rules_from_peg};

    fn main() {
        let rules = rules_from_peg(
            r#"

    main            =   letter letter_or_num+

    letter          =   [a-zA-Z]

    letter_or_num   =   letter
                    /   number

    number          =   [0-9]

            "#,
        ).map_err(|e| {
            println!("{}", e);
            panic!("FAIL");
        })
            .unwrap();

        println!("{:#?}", rules);

        let result = parse("a2Z", &rules);
        match result {
            Ok(ast) => println!("{:#?}", ast),
            Err(e) => println!("Error: {:?}", e),
        };
    }

The AST produced will be:

Rule(
    (
        "main",
        [
            Rule(
                (
                    "letter",
                    [
                        Val(
                            "a"
                        )
                    ]
                )
            ),
            Rule(
                (
                    "letter_or_num",
                    [
                        Rule(
                            (
                                "number",
                                [
                                    Val(
                                        "2"
                                    )
                                ]
                            )
                        )
                    ]
                )
            ),
            Rule(
                (
                    "letter_or_num",
                    [
                        Rule(
                            (
                                "letter",
                                [
                                    Val(
                                        "Z"
                                    )
                                ]
                            )
                        )
                    ]
                )
            )
        ]
    )
)

The AST type is:

pub enum Node {
    Val(String),
    Rule((String, Vec<Node>)),
    EOF,
}

Just it (remember, more information about the peg grammar bellow)

Example 2

You will configure a set of rules to parse.

The rule is composed of a name followed by an arrow and an expression to be parsed.

A basic example

Lets create the next grammar:

   main    =   "a" ( "bc" "c"
                   / "bcdd"
                   / b_and_c  d_or_z
                   )

   b_and_c =   "b" "c"
   d_or_z  =   "d" / "z"

Just from peg

extern crate dynparser;
use dynparser::{parse, rules_from_peg};

fn main() {
    let rules = rules_from_peg(
        r#"

    main    =   "a" ( "bc" "c"
                    / "bcdd"
                    / b_and_c  d_or_z
                    )

    b_and_c =   "b" "c"
    d_or_z  =   "d" / "z"

        "#,
    ).unwrap();

    assert!(parse("abcz", &rules).is_ok());
    assert!(parse("abcdd", &rules).is_ok());
    assert!(parse("abcc", &rules).is_ok());
    assert!(parse("bczd", &rules).is_err());
}

The exit will be the next AST

This is a dynamic parser, you can add rules at execution time.

pending: example

Generating the rules by hand with macros

You can create this grammar and parse the string "abcd" with macros like:

#[macro_use]
extern crate dynparser;
use dynparser::parse;

fn main() {
    let rules = rules!{
       "main"   =>  and!{
                        lit!("a"),
                        or!(
                            and!(lit!("bc"), lit!("c")),
                            lit!("bcdd"),
                            and!(
                                ref_rule!("b_and_c"),
                                ref_rule!("d_or_z")
                            )
                        )
                    },
        "b_and_c"  => and!(lit!("b"), lit!("c")),
        "d_or_z"  => or!(lit!("d"), lit!("z"))
    };

    let result = parse("abcd", &rules);
    match result {
        Ok(ast) => println!("{:#?}", ast),
        Err(e) => println!("Error: {:?}", e),
    };
}

Adding a rule on execution time:

#[macro_use]  extern crate dynparser;
use dynparser::parse;
fn main() {
    let rules = rules!{
       "main"   =>  and!{
                        rep!(lit!("a"), 1, 5),
                        ref_rule!("rule2")
                    }
    };

    let rules = rules.add("rule2", lit!("bcd"));

    assert!(parse("aabcd", &rules).is_ok())
}

Of course, you could need to add (or merge) several rules at once

And of course, you can add several rules at once

#[macro_use]  extern crate dynparser;
use dynparser::parse;
fn main() {
    let r = rules!{
       "main"   =>  and!{
                        rep!(lit!("a"), 1, 5),
                        ref_rule!("rule2")
                    }
    };
    let r = r.merge(rules!{"rule2" => lit!("bcd")});
    assert!(parse("aabcd", &r).is_ok())
}

merge takes the ownership of both set of rules and returns a "new" (in fact modified) set of rules. This helps to reduce mutability

"main" rule is the entry point.

More information in doc (link pending)

PEG

Rule elements enumeration

Examples below

token	Description
`=`	On left, symbol, on right expresion defining symbol
`symbol`	It's an string without quotes
`.`	Any char
`"..."`	Literal delimited by quotes
`space`	Separate tokens and Rule concatenation (and operation)
`/`	Or operation
`(...)`	A expression composed of sub expresions
`?`	One optional
`*`	Repeat 0 or more
`+`	Repeat 1 or more
`!`	negate expression
`[...]`	Match chars. It's a list or ranges (or both)
`->`	pending...
`:`	pending...

Let's see by example

Rules by example

A simple literal string.

main = "Hello world"

Concatenation (and)

main = "Hello "  "world"

Referencing symbols (rule)

Symbol

main = hi
hi   = "Hello world"

Or /

main = "hello" / "hi"

Or multiline

main
    = "hello"
    / "hi"
    / "hola"

Or multiline 2

main = "hello"
     / "hi"
     / "hola"

Or disorganized

main = "hello"
     / "hi" / "hola"

Parenthesis

main = ("hello" / "hi")  " world"

Just multiline

Multiline1

main
    = ("hello" / "hi")  " world"

Multiline2

main
    = ("hello" / "hi")
    " world"

Multiline3

main = ("hello" / "hi")
     " world"

It is recomended to use or operator / on each new line and = on first line, like

Multiline organized

main = ("hello" / "hi")  " world"
     / "bye"

One optional

main = ("hello" / "hi")  " world"?

Repetitions

main         = one_or_more_a / zero_or_many_b
one_or_more  = "a"+
zero_or_many = "b"*

Negation will not move current possition

Next example will consume all chars till get an "a"

Negation

main = (!"a" .)* "a"

Consume till

comment = "//" (!"\n" .)*
        / "/*" (!"*/" .)* "*/"

Match a set of chars. Chars can be defined by range.

number  = digit+ ("." digit+)?
digit   = [0-9]
a_or_b  = [ab]
id      = [_a-zA-Z][_a-zA-Z0-9]*

a_or_b_or_digit  = [ab0-9]

Simple recursion

one or more "a" recursive

as  = "a" as
    / "a"

//  simplified with `+`
ak = "a"+

Recursion to match parenthesis

Recursion match par

match_par = "(" match_par ")"
          / "(" ")"

Grammar bellow (on hacking the code)...

Text

Hey, I'm a text parser, I need a text to parse ;-P

If you want to parse text indentation sensitive, I recomend you the lib indentation_flattener

pending...

A grammar for the grammar

A grammar to define the grammar to be parsed by de parser. ;-P

I will define the grammar using the this parser grammar definition rules.

A grammar is a set of rules.

A rule, is a symbol followed by = and an expression

grammar = rule+
rule    = symbol "="  expr

Here we relax the verification to keep the grammar as simple as possible. It's missing also the non significant spaces.

About the expression.

As you know, it's important to accept valid inputs, but also it's important to build an AST with proper pritority.

Next grammar:

main    =  "A" "B"  /  "B" "C"

It's equivalent to:

main    =  ("A" "B")  /  ("B" "C")

But not to:

main    =  (("A" "B")  /  "B") "C"

To represent this priority, the expression rule has to be defined in a descendant priority way:

expr            =   or_expr

or_expr         =   and_expr     ("/"  or_expr)*

and_expr        =   simpl_expr   (" "  and_expr)*

simpl_expr      =   "!" atom_or_par
                /   simpl_par ("*" / "+")

atom_or_par     =   (atom / parenth_expr)


parenth_expr    =   "("  expr ")"

Descendant definition

expr	Description
atom_or_par	It's an atom or a parenthesis experssion
rep_or_neg	It's not a composition of `and` or `or` expressions. It can have negation or repetitions
parenth	It's an expressions with parenthesis
and	Sequence of expressions separated by space
or	Sequence of expression separated by "/"

Now, it's the atom turn:

atom    =   literal
        /   match
        /   dot
        /   symbol

literal =   "\""  (!"\"" .)*  "\""
match   =   "["  ((.  "-"  .)  /  (.))+   "]"
dot     =   "."
symbol  =   [a-zA-Z0-9_]+

Hey, what about comments?

What about non significative spaces and carry return?

It will be defined on "_" symbol

main            =   grammar

grammar         =   rule+

rule            =   symbol  _  "="  _   expr  (_ / eof)

expr            =   or

or              =   and         ( _ "/" _  or  )*

and             =   rep_or_neg  (   " " _  and )*

rep_or_neg      =   atom_or_par ("*" / "+" / "?")?
                /   "!" atom_or_par

atom_or_par     =   (atom / parenth)


parenth         =   "("  _  expr  _  ")"



atom            =   literal
                /   match
                /   dot
                /   symbol

literal         =   _"  (!_" .)*  _"
_"              =   "\u{34}"

match           =   "["
                        (
                            (mchars+  mbetween*)
                            / mbetween+
                        )
                    "]"
mchars          =   (!"]" !(. "-") .)+
mbetween        =   (.  "-"  .)

dot             =   "."
symbol          =   [_'a-zA-Z0-9][_'"a-zA-Z0-9]+


_               =  (  " "
                      /   eol
                      /   comment
                   )*

eol             = ("\r\n"  \  "\n"  \  "\r")

comment         =  "//" (!eol .)* "/n"
                /  "/*" (!"*/" .)* "*/"

That's ok an works fine, but we can inprove error messages...

In order to improve error messages, would be interesting to modify the grammar.

Look this code:

pending...

At the beggining it finished with no errors, but not consuming the hole input. Wich is an error.

Showing an error informing that we didn't consume full input, is not the best.

pending...

The reason is on

pending...
...
and_expr        =   compl_expr  (  " "  _  and_expr)*
...

Here, we said, "hey, try to look for a sequence, or not *"

And is not, then the parser say, I matched the rule, I have to continue verifying other previus branches. But there are no previus partial applied brunchs. Then the parser ends not consuming all the input.

To improve error messages, would be interesting to have something like:

pending...
parenth_expr    = "(" * expr _ ")"
                / "(" _ expr _ -> error("mismatch parenthesis")

The or brunch will be executed if there is no closing parenthesis and we can write an specific error message.

Parsing the parser

Or... how to parse yourself

Remember, we started with the concept of a simple parser...

Starting with a set of rules and the input to process, we will generate the AST

simple_parser

On this, we added an additional step to generate the rules from a peg grammar avoiding written by hand on code.

Then, we have a parser that accepts peg grammars.

Now instead of giving the set of rules, we can provide a peg definition and the input to genterate the AST

basic_diagram

But the input peg grammar has to be processed (parsed). We have to writte rules_from_peg code to parse the input peg

Who's gonna parse the grammar peg? A parser?

Let me think... Ummmm!!!

I'm a parser!!!!!

We have a feature that allows us to generate the Rust code for an AST tree generated from a peg grammar. Oh?!

So the code to parse the peg grammar will be generated automatically with this parser

automatic_diagram

Then we will generate automatically rules_from_peg recursively.

Once this is done, we can now use the parser in a classic way

Remember, a normal parsing, we have two inputs.

The peg grammar
The input text

Now, for start with, both inputs will be a peg grammar defining it self (a peg grammar defining a peg grammar)

input: peg grammar defining itself
running rules_from_peg to generate a set of rules for this peg grammar
With the two previous points, we will parse creating the AST for the peg grammar
Now we will call ast::genetarte_rust to generate the code for rules_from_peg
We will insert this code on the parser
And we are ready to parse an input with a peg grammar to generate the AST

Why to do that?

First, it's possible and a great test.

Second. If we want to modify our peg grammar, it's boring and error prone to write the code manually.

Using a peg file to generate automatically rules_from_peg, keeps document and code as one (always synchronized)

diagrams generation

echo "[ input peg ] -- rules_from_peg --> [ rules ][ input text ], [ rules ] --> { end: back,0; } [ AST ]" | graph-easy --dot | dot -Tpng -o doc_images/basic.png

echo "[ rules ][ input text ], [ rules ] --> { end: back,0; } [ AST ]" | graph-easy --dot | dot -Tpng -o doc_images/simple_parser.png

echo "
[input peg \\n
  for peg grammar ] -- [rules_from_peg] { shape: none; } -->
                [rules_peg_gramm] { label: rules\\n
                                        for peg grammar }
[input peg \\n
  for peg grammar ], [ rules_peg_gramm ] -- parse --> { end: back,0; } [ AST ]

[AST] ~~ generate rust ~~> [rules_from_peg] { shape: none; }

" | graph-easy --dot | dot -Tpng -o doc_images/automatic_diagram.png

dynparser 0.1.0

DynParser

Usage

Modifications

TODO

Basic example

Just from peg

Example 2

Just from peg

Generating the rules by hand with macros

PEG

Rule elements enumeration

Rules by example

Text

A grammar for the grammar

Parsing the parser

diagrams generation