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https://github.com/shouya/gximemo

Ĝi kredas ĝi memo: A PEG parser engine
https://github.com/shouya/gximemo

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Ĝi kredas ĝi memo: A PEG parser engine

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# Ĝi Memo (GxiMemo)

Ĝi kredas ĝi memo: yet another compiler compiler. (PEGs)



## Description

### What is this project

GxiMemo is a project that aims to construct a PEG compiler that

is capable to compile its own language specification.



This project is mostly a toy, because although it works, it is not as

practically usable like other excellent compilers in Haskell such as

Parsec.



### Why is this project

Abstraction is attractive to me. Yet I finished my previous project,

"revo", a functionally complete scheme interpreter, I started to think

beyond what I can do next. The idea of building a compiler compiler rose

at that time, since it seems a compiler compiler is a kind of, at

least a part of, meta-compiler.



### Ĝi kredas ĝi memo

In Esperanto, "Ĝi kredas ĝi memo" means "It creates itself".

The aphorism describes such a self-compiling process, and that

explains how GxiMemo works.



Replacing the subject of "Ĝi kredas ĝi memo" with a hole, we can

construct an interesting quinification of the sentence.



> "X kredas ĝi memo" kredas ĝi memo.



## Details

### Components of GxiMemo

GxiMemo mainly separates into three parts, the parser, the

language, and the specification. The different components are

related to the other.



![gximemo_components](https://shouya.github.io/gximemo/components.svg)



The parser part (`Parser.hs`) provides a complete PEG parser. It can be fed with a

group of parsing rules and a bunch of input text, then produce a

matched result.



The GxiMemo language part (`GxiMemo.hs`) contains a full class of

specification rules for its own language, and the conversion functions

that converts the matched result into the specification rules. The

process of translating the matched data into specification is the key

of this project. With this part it would be able to define a BNF

specification in a succinct and convenient syntax.



Besides, there is a language specification file (`Gxi.memo`). The file

contains a group of language specification describing itself. Parsing

which with the previous two parts, it will get a completely same rule

set as that used to parse itself specified in `GxiMemo.hs`.



### Interfaces



Below are the main interfaces exported and are available for advanced

usages.



#### `Parser.hs`

```haskell

type RuleName = String

type RulePair = (RuleName, Pattern)

type RuleMap = M.Map RuleName Pattern



data RepTime = RTInt Integer -- n-times

             | RTInf         -- infinity

             deriving (Show,Eq)



manyTimes :: Pattern -> Pattern

anyTimes :: Pattern -> Pattern

optional :: Pattern -> Pattern



data Pattern = Atom String

             | Rule String

             | RuleX String  -- rule that only do matching but ignoring the result

             | Repetition Pattern RepTime RepTime -- pat, minTime, maxTime

             | Choice [Pattern]

             | Sequence [Pattern]

             | NegativeLookahead Pattern

             | PositiveLookahead Pattern

             deriving (Eq)



instance Show Pattern



data MatchData = MAtom String

               | MList [MatchData]

               | MPair (RuleName, MatchData)

               deriving (Eq)



instance Show MatchData



isMPair :: MatchData -> Bool

getMPair :: MatchData -> (RuleName, MatchData)

isMList :: MatchData -> Bool

getMList :: MatchData -> [MatchData]

isMAtom :: MatchData -> Bool

getMAtom :: MatchData -> String



mInspect :: MatchData -> String

mToString :: MatchData -> String



parseI :: Pattern -> ParseResult

```



### `GxiMemo.hs`

```haskell

rules :: [RulePair]

parse :: String -> RuleMap -> String -> Maybe MatchData

simplify :: MatchData -> MatchData

simplifyGM :: MatchData -> MatchData

toPatternPair :: MatchData -> Maybe RulePair

toPattern :: MatchData -> Maybe Pattern

parseToRuleList :: String -> Maybe [RulePair]

```



Use `parseToRuleList` to convert a specification string into rule

pairs. And then use `parse`, fed with the text to be parsed, rule map

build from rule pairs, and the starting rule name, to generate the

result of matching.



### Demonstration

A demonstration of the GxiMemo language spec conversion has been shown

in `Main.hs`. Enter the following command to run it.



```bash

$ cd GxiMemo

$ runghc Main.hs

```



## License



The MIT License (MIT)



Copyright (c) 2013-2014 Shou Ya



Permission is hereby granted, free of charge, to any person obtaining a copy of

this software and associated documentation files (the "Software"), to deal in

the Software without restriction, including without limitation the rights to

use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of

the Software, and to permit persons to whom the Software is furnished to do so,

subject to the following conditions:



The above copyright notice and this permission notice shall be included in all

copies or substantial portions of the Software.



THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS

FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR

COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER

IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN

CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.