Hello,
I'm attempting to write a parser for files that look like this:
Bruker Nano GmbH Berlin, Germany
Esprit 1.9
Date: 02/05/2013 10:06:49 AM
Real time: 15000
Energy Counts
-0.474 0
.....
The line before the ellipsis is repeated many times (such lines
represents a spectrum). I need to be able to extract numbers from lines
containing
* Roger Mason
Thus far, I have: -- derived from RWH -- file: ch16/csv2.hs import Text.ParserCombinators.Parsec
headerLines = endBy csvFile endHeader csvFile = endBy line eol line = sepBy cell (char ',') cell = many (noneOf ",\n") eol = char '\n'
parseCSV :: String -> Either ParseError [[String]] parseCSV input = parse csvFile "(unknown)" input
parseHDR :: String -> Either ParseError [[String]] parseHDR input = parse headerLines "(unknown)" input
endHeader = string "Energy Counts"
This loads into GHCi (7.6.2) OK. However, when I test it:
parseHDR "Bruker Nano GmbH Berlin, Germany\nEsprit 1.9\n\nDate: 02/05/2013 10:06:49 AM\nReal time: 15000\nEnergy Counts"
Not in scope: `parseHDR'
which makes sense because
ghci> :t endHeader
<interactive>:1:1: Not in scope: `endHeader'
Clearly, my naiive implementation of endHeader is no good.
Hi Roger, "Not in scope" means that that thing is not defined. So it's not a problem with your implementation, but with the way you load it. If you copy-paste your ghci session here, you may get further help. Roman
Hi Roman, On 05/21/2013 12:36 PM, Roman Cheplyaka wrote:
Clearly, my naiive implementation of endHeader is no good. Hi Roger,
"Not in scope" means that that thing is not defined.
So it's not a problem with your implementation, but with the way you load it.
If you copy-paste your ghci session here, you may get further help.
Roman
Starting with a clean ghci session I get this: ghci> :l csv.hs [1 of 1] Compiling Main ( csv.hs, interpreted ) csv.hs:15:24: Couldn't match type `[Char]' with `Char' Expected type: Text.Parsec.Prim.Parsec String () [[String]] Actual type: Text.Parsec.Prim.ParsecT String () Data.Functor.Identity.Identity [[[[Char]]]] In the first argument of `parse', namely `headerLines' In the expression: parse headerLines "(unknown)" input In an equation for `parseHDR': parseHDR input = parse headerLines "(unknown)" input Failed, modules loaded: none. Thanks, Roger This electronic communication is governed by the terms and conditions at http://www.mun.ca/cc/policies/electronic_communications_disclaimer_2012.php
* Roger Mason
Hi Roman,
On 05/21/2013 12:36 PM, Roman Cheplyaka wrote:
Clearly, my naiive implementation of endHeader is no good. Hi Roger,
"Not in scope" means that that thing is not defined.
So it's not a problem with your implementation, but with the way you load it.
If you copy-paste your ghci session here, you may get further help.
Roman
Starting with a clean ghci session I get this:
ghci> :l csv.hs [1 of 1] Compiling Main ( csv.hs, interpreted )
csv.hs:15:24: Couldn't match type `[Char]' with `Char' Expected type: Text.Parsec.Prim.Parsec String () [[String]] Actual type: Text.Parsec.Prim.ParsecT String () Data.Functor.Identity.Identity [[[[Char]]]] In the first argument of `parse', namely `headerLines' In the expression: parse headerLines "(unknown)" input In an equation for `parseHDR': parseHDR input = parse headerLines "(unknown)" input Failed, modules loaded: none.
So this is the real error. If you read it carefully, it says that it expected [[String]] but got [[[[Char]]]] (i.e. [[[String]]]) as a result of the headerLines parser. I don't have time right now to look closer at your code, but I suggest studying the types of combinators you use (such as endBy) and trying to write down type signatures for the rest of the values you define. This way you'll find the error and better understand your program. A useful trick is to start ghci with -fdefer-type-errors and use ":t" to inspect types of various expressions that you encounter. Roman
Thank you. Roger On 05/21/2013 03:15 PM, Roman Cheplyaka wrote:
So this is the real error. If you read it carefully, it says that it expected [[String]] but got [[[[Char]]]] (i.e. [[[String]]]) as a result of the headerLines parser. I don't have time right now to look closer at your code, but I suggest studying the types of combinators you use (such as endBy) and trying to write down type signatures for the rest of the values you define. This way you'll find the error and better understand your program. A useful trick is to start ghci with -fdefer-type-errors and use ":t" to inspect types of various expressions that you encounter. Roman
This electronic communication is governed by the terms and conditions at http://www.mun.ca/cc/policies/electronic_communications_disclaimer_2012.php
participants (2)
-
Roger Mason -
Roman Cheplyaka