Parse Text input and get Text output (not String) with Parsec3 - string

Question

I see that Parsec3 handles Text (not String) input, so I would like to convert an old String parser to get Text output. Other libraries I am using also uses Text, so that would reduce the number of conversions needed.
Now, the parsec3 library seems to do what it says (handle both Text and String input), this example is from within gchi:
Text.Parsec.Text Text.Parsec Data.Text> parseTest (many1 $ char 's') (pack "sss")
"sss"
Text.Parsec.Text Text.Parsec Data.Text> parseTest (many1 $ char 's') "sss"
"sss"
So, both Text (first case) and String (second case) works.
Now, In my real, converted, parser (sorry I have to piece together some remote parts of the code here to make a complete example)
{-# LANGUAGE OverloadedStrings #-}
data UmeQueryPart = MidQuery Text Text MatchType
data MatchType = Strict | Fuzzy deriving Show
funcMT :: Text -> MatchType
funcMT mt = case mt of
"~" -> Fuzzy
_ -> Strict
midOfQuery :: Parser UmeQueryPart
midOfQuery = do
spaces
string "MidOf"
spaces
char '('
spaces
clabeltype <- many1 alphaNum
spaces
sep <- try( char ',') <|> char '~'
spaces
plabeltype <- many1 alphaNum
spaces
char ')'
spaces
return $ MidQuery (pack plabeltype) (pack clabeltype) (funcMT sep)
I find myself with a lot of errors like this with regards to the funcMT call
UmeQueryParser.hs:456:96:
Couldn't match type ‘[Char]’ with ‘Text’
Expected type: Text
Actual type: String
In the first argument of ‘funcMT’, namely ‘sep’
In the fifth argument of ‘ midOfQuery’, namely ‘(funcMT sep)’
and if I don't explicitly pack the captures text in the code sample above, this:
UmeQueryParser.hs:288:26:
Couldn't match expected type ‘Text’ with actual type ‘[Char]’
In the first argument of ‘ midOfQuery’, namely ‘(plabeltype)’
In the second argument of ‘($)’, namely
‘StartQuery (plabeltype) (clabeltype) (funcMT sep)’
So, it seems that I need to convert captured strings explicitly to Text in the output.
So, why do I need to go through a step converting from Stringor Char to Text when the point was to do Text -> Text parsing?

Answer 1

You could just make your own Text parser, something simple like
midOfQuery :: Parser UmeQueryPart
midOfQuery = do
spaces
lexeme $ string "MidOf"
lexeme $ char '('
clabeltype <- lexeme alphaNums
sep <- lexeme $ try (char ',') <|> char '~'
plabeltype <- lexeme alphaNums
lexeme $ char ')'
return $ MidQuery plabeltype clabeltype (funcMT sep)
where
alphaNums = pack <$> many1 alphaNum
lexeme p = p <* spaces
or, slightly more compact (but I think still more readable):
midOfQuery :: Parser UmeQueryPart
midOfQuery = spaces *> lexeme (string "MidOf") *> parens (toQuery <$> lexeme alphaNums <*> lexeme matchType <*> lexeme alphaNums)
where
lexeme :: Parser a -> Parser a
lexeme p = p <* spaces
alphaNums = pack <$> many1 alphaNum
parens = between (lexeme $ char '(') (lexeme $ char ')')
matchType = Fuzzy <$ char '~' <|>
Strict <$ char ','
toQuery cLabelType sep pLabelType = MidQuery pLabelType cLabelType sep