Experimental Physics and
Industrial Control System

On Thursday 01 November 2007 08:18, Heinrich du Toit wrote:
> Oops.. actually I need like the parser part..
> Ie. what bison does :)
>
> On Thu, 2007-11-01 at 08:31 +0200, Heinrich du Toit wrote:
> > Hi
> >
> > Is there 'n lexical analyzer for .db files?
> >
> > I guess there must be something in epics BASE somewhere?
> > But is it written in something like flex that can easily be
> > extended/used or is it some custom code nightmare?
> >
> > O let me explain.
> > I want to make some sort of .db file pre-processor that can do some
> > modifications. Mainly macro expansion type stuff.
> > And this I want to use so that some rule stuff can be written in
> > Macro's and not in long complex records and hopefully make it easier to
> > maintain and understand and change. And then maybe also handle some
> > other stuff with the pre-processor to keep thing consistently linked
> > ect... making it more reliable and less prone to human error. Plus the
> > person working with it might not fully understand all the internal
> > stuff of 'n db.

FWIW, attached you find a parser for the db file syntax written in Haskell 
using a parser combinator library. Took me about 20 minutes to write and 
worked out of the box.

Cheers
Ben

module ParseEpics where

import Text.ParserCombinators.Parsec

quadruple p q s t = do
  rp <- p
  symbol ","
  rq <- q
  symbol ","
  rs <- s
  symbol ","
  rt <- t
  return (rp,rq,rs,rt)

pair p q = do
  rp <- p
  symbol ","
  rq <- q
  return (rp,rq)

braces p = do
  symbol "{"
  r <- p
  symbol "}"
  return r

parens p = do
  symbol "("
  r <- p
  symbol ")"
  return r

item = lexeme (quoted <|> bareword)

symbol = lexeme . string

lexeme p = do
  r <- p
  skipWhite
  return r

bareword = many1 (alphaNum <|> oneOf "_-:.[]<>;")

quoted = do
  char '"'
  s <- manyTill (try escquote <|> notquote) (char '"')
  return s

notquote = noneOf "\""
escquote = string "\\\"" >> return '"'

skipWhite = skipMany white

white = blank <|> comment

blank = skip (oneOf " \n\t\v")

comment = char '#' >> skipMany (noneOf "\n")

skip p = p >> return ()

{-# LANGUAGE FlexibleContexts #-}
--module ParseDb (parseEpicsDb) where

import Data.Collections
import MonadLib hiding (try)
import Monads (runException)
import Text.ParserCombinators.Parsec

-- import Gadgets (EpicsRecord(..),Attributes)
import ParseEpics

type Attributes = StdMap String String

data EpicsRecord = ER {
    erType :: String,
    erName :: String,
    erFieldDefs :: Attributes
  } deriving Show

type EpicsDb = [EpicsRecord]

parseEpicsDb :: ExceptionM m String => SourceName -> String -> m EpicsDb
parseEpicsDb filename input = case parse epicsDb filename input of
  Right records -> return records
  Left parseErr -> raise (show parseErr)

epicsDb = skipWhite >> many epicsRecord

epicsRecord = do
  symbol "record"
  (rectype,recname) <- parens (pair item item)
  recfields <- braces fields
  return $ ER { erType=rectype, erName=recname, erFieldDefs=recfields }

fields = fmap fromList (many field)
  
field = do
  symbol "field"
  parens (pair item item)

-- test
main = do --getContents >>= parseTest epicsDb
  input <- getContents
  case runException (parseEpicsDb "" input) of
    Left err -> putStrLn err
    Right rs -> putStr . unlines . map show $ rs

References:

lexical analyzer for .db? Heinrich du Toit

Re: lexical analyzer for .db? Heinrich du Toit

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