type signature of parsec functions and how to warp them up.
I have some different parsers of Parsec to use in a project, and I want to make a warp function to make the testing easy. here is some of my body of parser : they all has type of "parsecT ***" stringSet :: ParsecT String u Identity [String] intSet :: ParsecT String u Identity [Integer] tupleSet :: ParsecT String u Identity [(String, String)] all of the returned type are instance of 'Show'. then I write these warp function: ------------------ import System.IO import Data.Functor.Identity (Identity) import Text.Parsec.Prim (ParsecT, runParserT, parse, Stream) runIOParse :: (Show a) => ParsecT String u Identity a -> String -> IO () runIOParse pa fn = do inh <- openFile fn ReadMode outh <- openFile (fn ++ ".parseout") WriteMode instr <- hGetContents inh let result = show $ parse pa fn instr hPutStr outh result hClose inh hClose outh -------------------
:l RunParse.hs
RunParse.hs:12:31: Could not deduce (u ~ ()) from the context (Show a) bound by the type signature for runIOParse :: Show a => ParsecT String u Identity a -> String -> IO () at RunParse.hs:(7,1)-(15,15) `u' is a rigid type variable bound by the type signature for runIOParse :: Show a => ParsecT String u Identity a -> String -> IO () at RunParse.hs:7:1 Expected type: Text.Parsec.Prim.Parsec String () a Actual type: ParsecT String u Identity a In the first argument of `parse', namely `pa' In the second argument of `($)', namely `parse pa fn instr' Failed, modules loaded: none. ------------------- then I modify the type signature of 'runIOParse': runIOParse :: (Show a) => ParsecT String () Identity a -> String -> IO () then load again
:l RunParse.hs
RunParse.hs:12:25: Could not deduce (Stream String Identity t0) arising from a use of `parse' from the context (Show a) bound by the type signature for runIOParse :: Show a => ParsecT String () Identity a -> String -> IO () at RunParse.hs:(7,1)-(15,15) Possible fix: add (Stream String Identity t0) to the context of the type signature for runIOParse :: Show a => ParsecT String () Identity a -> String -> IO () or add an instance declaration for (Stream String Identity t0) In the second argument of `($)', namely `parse pa fn instr' In the expression: show $ parse pa fn instr In an equation for `result': result = show $ parse pa fn instr Failed, modules loaded: none. ------------------- I also tried some 'possible fix' in the information, but it still failed to pass the compiler. Main Question: **** How can I warp a parsec function interface for do the IO test with different 'ParsecT String u Identity a'? -- ---------------- 吴兴博 Wu Xingbo
It seems weird:
first ghci failed to load this file:
file: RunParse.hs
-------------------
module RunParse where
import System.IO
import Data.Functor.Identity (Identity)
----import Text.Parsec --------first, no this
line-------what about this line ???
import Text.Parsec.Prim (Parsec, parse, Stream)
runIOParse :: (Show a) => Parsec String () a -> String -> IO ()
runIOParse pa fn =
do
inh <- openFile fn ReadMode
outh <- openFile (fn ++ ".parseout") WriteMode
instr <- hGetContents inh
let result = case parse pa fn instr of
Right rs -> show rs
Left err -> "error"
hPutStr outh result
hClose inh
hClose outh
------------------
ghci tell me:
-----------------
RunParse.hs:13:23:
Could not deduce (Stream String Identity t0)
arising from a use of `parse'
from the context (Show a)
bound by the type signature for
runIOParse :: Show a => Parsec String () a -> String -> IO ()
at Sim/Std/RunParse.hs:(8,1)-(18,15)
Possible fix:
add (Stream String Identity t0) to the context of
the type signature for
runIOParse :: Show a => Parsec String () a -> String -> IO ()
or add an instance declaration for (Stream String Identity t0)
In the expression: parse pa fn instr
In the expression:
case parse pa fn instr of {
Right rs -> show rs
Left err -> "error" }
In an equation for `result':
result
= case parse pa fn instr of {
Right rs -> show rs
Left err -> "error" }
------------------
I just add one line of import and ghci:
import Text.Parsec
then ghci loaded it succeed!
It seems I didn't uses any functions from this import.
what goes wrong?
2011/6/17 吴兴博
I have some different parsers of Parsec to use in a project, and I want to make a warp function to make the testing easy.
-- ---------------- 吴兴博 Wu Xingbo
On Fri, Jun 17, 2011 at 01:53, 吴兴博
I just add one line of import and ghci:
import Text.Parsec
then ghci loaded it succeed!
It seems I didn't uses any functions from this import.
what goes wrong?
I think the usual cause of that is that one or more necessary typeclass instances got defined by the import. -- brandon s allbery allbery.b@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms
I also tried to use 'import Text.Parsec ()'
It works, now I'm wondering does '()' really hide everything.
2011/6/17 Brandon Allbery
I think the usual cause of that is that one or more necessary typeclass instances got defined by the import.
-- brandon s allbery allbery.b@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms
-- ---------------- 吴兴博 Wu Xingbo
On 17 June 2011 16:19, 吴兴博
I also tried to use 'import Text.Parsec ()' It works, now I'm wondering does '()' really hide everything.
Everything except type class instances. -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com
On Fri, Jun 17, 2011 at 02:19, 吴兴博
I also tried to use 'import Text.Parsec ()' It works, now I'm wondering does '()' really hide everything.
You just confirmed that it's instances being imported; instances are global and cannot be hidden, so "import Module ()" imports all of the instances defined in Module but none of the functions. -- brandon s allbery allbery.b@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms
participants (3)
-
Brandon Allbery -
Ivan Lazar Miljenovic -
吴兴博