"parse error on input" in Haskell if-then-else conditional

Question

The following do block throws the error "parse error on input `conn'" when I attempt to compile it. I have tried many different configurations of the if-then-else statement to no avail. The database logic worked before I added the conditional, so there isn't a problem with that. Do I have too many lines in the else? Is there any way to fix this without completely revamping the logic?

main = do
   contents <- BL.getContents
   let myData = decode contents :: Maybe Data
   if maybe True (\x -> result x /= "success") myData
      then error ("JSON download failed")
      else let myTrades = process myData
         conn <- connectSqlite3 "trades.db"
         insert <- DB.prepare conn "INSERT INTO trades VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?);"
         DB.executeMany insert $ map (\xs -> map DB.toSql xs) myTrades
         DB.commit conn
         DB.disconnect conn

There ended up being two problems with this. The first was the one described in the answer below; I needed "do" after "else". Additionally, the last four lines needed to be indented to be in the same column as the "l" in "let". — Mike
– Mike, Commented May 31, 2013 at 14:46

sclv · Accepted Answer · 2013-05-30 22:07:55Z

5

You need to introduce a do block after the else like so:

  else do let myTrades = process myData
          conn <- connectSqlite3 "trades.db"
          insert <- DB.prepare conn "INSERT INTO trades VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?);"
          DB.executeMany insert $ map (\xs -> map DB.toSql xs) myTrades
          DB.commit conn
          DB.disconnect conn

answered May 30, 2013 at 22:07

sclv

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1 Comment

Mike Over a year ago

I also needed to align the last four columns with the "l" in "let". This was the primary problem, though. Thanks.

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