source = "#123456789012345678901234567890123456789012345678901234567890\n\
\SVCLFOWLER 10101MS0120050313.........................\n\
\SVCLHOHPE 10201DX0320050315........................\n\
\SVCLTWO x10301MRP220050329..............................\n\
\USGE10301TWO
x50214..7050329..............................."
type ConfigLine = (String, [(String, (Int, Int))])
type Configuration = [ConfigLine]
type KeyVal = (String, String)
type Header = String
type Entry = (Header, [KeyVal])
config :: Configuration
config = [("SVCL", [("CustomerName", (4, 18)),
("CustomerID", (19, 23)),
("CallTypeCode", (24, 27)),
("DateOfCallString", (28, 35))]),
("USGE", [("CustomerID", (4, 8)),
("CustomerName", (9, 22)),
("Cycle", (30, 30)),
("ReadDAte", (31, 36))])]
getRange :: Int -> Int -> [a] -> [a]
getRange a b l = take (b-a+1) $ drop a l
lineToFields :: String -> [(Int,Int)] -> [String]
lineToFields line points = map (fieldFromTo line) points
where fieldFromTo line (x,y) = getRange x y line
lineType :: String -> String
lineType = getRange 0 3
applyConfig :: String -> ConfigLine -> [KeyVal]
applyConfig line (ckey, cval) =
if lineType line == ckey
then zip names $ lineToFields line points
else []
where part = unzip cval
names = fst part
points = snd part
parseLine :: Configuration -> String -> Entry
parseLine cnf line = (header, parsed)
where rawData :: [[KeyVal]]
rawData = map (applyConfig line) cnf
parsed :: [KeyVal]
parsed = head $ dropWhile null rawData
header = lineType line
parse :: Configuration -> [String] -> [Entry]
parse cnf lines = map (parseLine cnf) lines
run = parse config $ filter noComment $ lines source
where noComment = \x -> (head x) /= '#'
====== Output
*Main> run
[("SVCL",[("CustomerName","FOWLER
"),("CustomerID","10101"),("CallTypeCode","MS01"),("DateOfCallString","20050313")]),("SVCL",[("CustomerName","HOHPE
"),("CustomerID","10201"),("CallTypeCode","DX03"),("DateOfCallString","20050315")]),("SVCL",[("CustomerName","TWO
x"),("CustomerID","10301"),("CallTypeCode","MRP2"),("DateOfCallString","20050329")]),("USGE",[("CustomerID","10301"),("CustomerName","TWO
x"),("Cycle","7"),("ReadDAte","050329")])]
*Main>
Yoel Jacobsen wrote:
It seems that Martin Fowler's article "Language Workbenches: The
killer-App for Domain Specific Languages?" -
http://www.martinfowler.com/articles/languageWorkbench.html - has
generated some nice dynamic solution where a configuration file is
written in the same language as the program. Notable examples are lisp -
http://lispm.dyndns.org/news?ID=NEWS-2005-07-08-1 and python -
http://billionairebusinessman.blogspot.com/2005/09/drop-that-schema-and-put-your-hands-in.html
I'm trying to create an _elegant_ solution in Haskell. But I'm stuck.
Since the native record-like access in Haskell syntax is using labelled
fields in datatype decleration but the later are strictly compile-time.
Therefore, if I compile my program and add a field in the configuration
file (written in Haskell, using, for instance hs-plugins), I'll need to
recompile the data declaration as well.
Further, what is the type of the parser? Consider the following
implementation:
source = "#123456789012345678901234567890123456789012345678901234567890\n\
\SVCLFOWLER 10101MS0120050313.........................\n\
\SVCLHOHPE 10201DX0320050315........................\n\
\SVCLTWO x10301MRP220050329..............................\n\
\USGE10301TWO x50214..7050329..............................."
data Configuration = Config String [(String, Int, Int)]
config = [
Config "SVCL" [("CustomerName", 4, 18),
("CustomerID", 19, 23),
("CallTypeCode", 24, 27),
("DateOfCallString", 28, 35)],
Config "USGE" [("CustomerID", 4, 8),
("CustomerName", 9, 22),
("Cycle", 30, 30),
("ReadDAte", 31, 36)]]
-- parse takes the configuration, a line from the source string and
generate a record
parse :: Configuration -> String -> Record
What is the type of Record?
Anyway, any elegant solution or a hint towards one are most welcome.
Thanks,
Yoel
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