July 2009 - Haskell-Cafe

Re: Monad Input/Output and Monad Transformers
by John Lato 03 Jul '09

03 Jul '09

> From: Maciej Piechotka <uzytkownik2(a)gmail.com> > > 1. Learning haskell I discovered that I/O should be avoided nearly 'at > all costs'. The problem is that the IO monad is the only one which have > more interactive work flow. There is Reader/Writer monad but in fact > AFAIU first one is about the environment and second one is about > logging. Implementation of Writer can be defined in terms of handles but > it is rather limited (either non-full implementation which may be > confusing or need of caching the result for pass etc.). > I'm not sure what you mean when you say that IO is the only monad with a "more interactive work flow". Do you mean that it allows interleaving of input and output? If so, I would ask what you're doing that makes this a concern. If it's for efficiency, don't worry about it. Haskell's laziness means that the language will take care of this for you. A good example is the bzlib[1] package; the "compress" function has type "ByteString -> ByteString" and automatically handles the chunking of data for you. If you need to partially process an input to determine how the rest of the input should be handled, there are many parser libraries (parsec[2], polyparse[3], etc.) that can either help with this directly or perhaps give ideas as to how you can handle it. You may also want to look at the iteratee[4] package. It sounds like it may accomplish what you're trying to do, although the interface is very different from what you specify. > > 2. I find writing monad transformers annoying. > Additionally if package defines transformer A and another transformer B > they need to be connected 'by hand'. > If this becomes onerous, I think the usual solution is to define custom lifting functions for the most commonly performed operations. However, my feeling is that you're probably trying to put together a monad stack to model what you're trying to do too soon, when you'd be better served trying to develop data structures and core functions that describe what you want to do. Of course, without more information this is just a guess. John Lato [1] http://hackage.haskell.org/package/bzlib [2] http://legacy.cs.uu.nl/daan/parsec.html, http://hackage.haskell.org/package/parsec [3] http://www.cs.york.ac.uk/fp/polyparse/, http://hackage.haskell.org/package/polyparse [4] http://okmij.org/ftp/Haskell/Iteratee/, http://hackage.haskell.org/package/iteratee

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Re: [Haskell-cafe] A Strict GCL Interpreter in Haskell
by Tillmann Rendel 03 Jul '09

03 Jul '09

Hi Hector, Hector Guilarte wrote: > I did that already, but it didn't work... Also, since this kind of error would be a run time error in my GCL Language, I don't want it to continue executing whenever an error is found, that's why I changed it back to just: > evalExpr:: Expr -> Tabla -> Int > > Instead of using the Either String Int... I think you misunderstand something. If you use (Expr -> Table -> Int), you are announcing: Whatever happens, I keep executing. If you use (Expr -> Table -> Either String Int), you are announcing: I may stop earlier because of some problem. Since may you want to stop earlier, you should use the second type. Let's look at a very small example, an interpreter for the following little language: data Expression = Literal Integer | Add Expression Expression | Divide Expression Expression Because of division by zero, an interpreter for this language may fail. So we have two kinds of return values: Sometimes we return a number, and sometimes we return an DivideByZero error. We can reflect that in a datatype: data Result = Number Integer | DivideByZeroError Now we can write our interpreter: eval :: Expression -> Result eval (Literal n) = Number n eval (Add a b) = case eval a of Number result_of_a -> case b of Number result_of_b -> Number (result_of_a + result_of_b) DivideByZeroError -> DivideByZeroError DivideByZeroError -> DivideByZeroError eval (Add a b) = case eval a of Number result_of_a -> case b of Number result_of_b -> if b == 0 then DivideByZeroError else Number (result_of_a + result_of_b) DivideByZeroError -> DivideByZeroError DivideByZeroError -> DivideByZeroError This interpreter will stop as soon as it encounters a division by zero, because we take care to return DivideByZeroError whenever we see a DivideByZeroError in one of the subterms. So you have to use an appropriate return type (like (Either String Int) or Result), and you have to pattern match on the result of "earlier" parts of your program, and propagate the error. Tillmann

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Haskellers at University of Edinburgh? (hackathon)
by Eric Kow 02 Jul '09

02 Jul '09

Hi Haskellers, I'm looking for people at the University of Edinburgh who have a swipe card with access to the Informatics Forum and could hang around on 29 August (or perhaps 6 Sep). Thanks! PS. You may also be interested in some Hackathon news: we've reserved a room at the ICFP venue suitable for up to 50 people, but we can only have it for 30 August. I'm still holding out for a two-day space, but if I don't hear back by mid-week, we'll settle for a single Haskell Hack Day, preceded by a more informal Haskell Hacking Expedition the day before (for example, camping in in a wifi-enabled pub for the day). -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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[ghc] kind of the function arrow
by Dominic Orchard 02 Jul '09

02 Jul '09

I was just playing around and noticed that the kind of the function arrow in GHC is (?? -> ? -> *) when I (naively) expected it to be (* -> * -> *). After looking at (http://hackage.haskell.org/packages/archive/ghc/6.10.2/doc/html/Type.html#5) I see that the kind of (->) means that the parameter type cannot be an unboxed tuple, whilst the result type can be anything. Why is this? After reading this documentation I would expect the kind (? -> ? -> *). I'm now wondering if the kind of (->) could cause problems if the following style of declaration is requried: > type FunArg a b = (a -> b, a) *Main> :k FunArg FunArg :: * -> * -> * By using type variables, whose default kind is *, the function type is fixed to use only boxed types. But if one wanted to allow unboxed type parameters the kind would be wrong, and an explicit kind signature of # or ? can't be given as they are not part of Haskell's source language. I guess my question is why the (?? -> ? -> *) kind on (->) and what to do if synonyms or data types over (->) are required such as the example just stated. I'm just curious. Thanks, Dominic

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Network.CGI -- practical web programming example.
by Edward Ing 02 Jul '09

02 Jul '09

I am somewhat new to haskell. It is amazing that I can actually write a CGI program using Network.CGI without really being comfortable with the Haskell type system. Especially when it involves monad transformations. So I decided that I better understand this. I looked at the Practical Web Programming examples to try to understand what is going on. I came up with a problem that might demonstrate my misunderstanding. I am wondering if you can answer questions I have. Code 1 is the example from PWP, Code 2 is my variation and it works so I am stumped by what the liftM is required. code 1>>> #!/usr/bin/runghc import Network.CGI import Text.XHtml import qualified Data.ByteString.Lazy as BS import Control.Monad (liftM) import Data.Maybe (fromJust) uploadDir = "../upload" fileForm = form ! [method "post", enctype "multipart/form-data"] << [afile "file", submit "" "Upload"] saveFile n = do cont <- (liftM fromJust) $ getInputFPS "file" let f = uploadDir ++ "/" ++ basename n liftIO $ BS.writeFile f cont return $ paragraph << ("Saved as " +++ anchor ! [href f] << f +++ ".") page t b = header << thetitle << t +++ body << b basename = reverse . takeWhile (`notElem` "/\\") . reverse cgiMain = do mn <- getInputFilename "file" h <- maybe (return fileForm) saveFile mn output $ renderHtml $ page "Upload example" h main = runCGI $ handleErrors cgiMain Code 2 (modifier) >>> import Network.CGI import Text.XHtml import qualified Data.ByteString.Lazy as BS import Control.Monad (liftM) import Data.Maybe (fromJust) uploadDir = "../upload" fileForm = form ! [method "post", enctype "multipart/form-data"] << [afile "file", submit "" "Upload"] saveFile n = do cont <- getInputFPS "file" let f = uploadDir ++ "/" ++ basename n liftIO $ BS.writeFile f (fromJust cont) return $ paragraph << ("Saved as " +++ anchor ! [href f] << f +++ ".") page t b = header << thetitle << t +++ body << b basename = reverse . takeWhile (`notElem` "/\\") . reverse cgiMain = do mn <- getInputFilename "file" h <- maybe (return fileForm) saveFile mn output $ renderHtml $ page "Upload example" h main = runCGI $ handleErrors cgiMain Questions === 1) Why did the author choose to insert "liftM" in function saveFile? It doesn't seem necessary in my version. 2) My background mainly is Java but here is my understanding of Monad Transforms. The CGIT m type carries around with it the CGI Request context and response contexts. The transformations (lifts) is similar to casting so that you can use the functions for specific manifestations but it also encapsulates the data. Is this correct? Edward

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A Strict GCL Interpreter in Haskell
by Hector Guilarte 02 Jul '09

02 Jul '09

Hi everyone! (First of all, I don't know Monads!) I made a GCL (Guarded Command Language) Compiler and Interpreter for my Languages and Machines course in my University with alex, happy and ghc. I still have a doubt: 1) Since Haskell is Lazy, and my GCL program is being interpreted in Haskell then my GCL is Lazy too (I know is not as simple as that but believe me, somehow it is behaving lazy). The problem is that it can't be lazy (said to me by my teacher on monday) so I tried using seq, but it didn't work, I'll paste the code after this: Programs in GCL like: a) var i : value main i <- 1 / 0 end b) var i : value main i <- 1 / 0; show i end c) var i : value var foo : array of 2 main i <- foo[42] end d) var i : value var foo : array of 2 main i <- foo[42]; show i end act like this: a and c finish interpretation b throws division by zero error and finish interpretation d throws index out of bounds error and finish interpretation Now the code: (it is in Spanish. ListLValue is a List of L-Values for the assigments, ListExpr is the list of Expressions to be assigned, Tabla is the Symbol Table (Data.Map), actualizarVar updates a Variable in the Symbol Table with the new value "valor", ActualizarArray updates the position "indice" of an array in the Symbol Table. evalExpr evaluates an arithmetic Expression and returns an Int. Inside evalExpr are the verifications for division by zero of modulo by zero.) evalAsignacion:: ListLvalue -> ListExpr -> Tabla -> Tabla evalAsignacion [] [] tabla = tabla evalAsignacion ((Lid id):valueList) (expr:exprList) tabla = let valor = (evalExpr expr tabla) in valor `seq` evalAsignacion valueList exprList (actualizarVar id valor tabla) evalAsignacion ((LArrayPosition id exprArray):valueList) (expr:exprList) tabla = let valor = (evalExpr expr tabla) indice = (evalExpr exprArray tabla) in valor `seq` indice `seq` evalAsignacion valueList exprList (actualizarArray id indice valor tabla) evalExpr:: Expr -> Tabla -> Int evalExpr expr tabla = let salida = (snd (evalAritmetico expr tabla)) in salida `seq` if (isLeft salida) then error (getLeft salida) else getRight salida --((Int,Int) is the Line and Colum, that's for error reporting) evalAritmetico :: Expr -> Tabla -> ((Int,Int),(Either String Int)) --LET ME KNOW IF YOU NEED THIS PART TOO Thanks in advance, Hector Guilarte

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Fun with type functions
by Simon Peyton-Jones 02 Jul '09

02 Jul '09

Friends Ken, Oleg, and I have finished Version 2 of our paper "Fun with Type Functions", which gives a programmer's tour of what type functions are and how they are useful. http://haskell.org/haskellwiki/Simonpj/Talk:FunWithTypeFuns If you have a moment to look at, and wanted to help us improve it, the above link goes to a wiki page where you can comment on the paper or discuss it. We still have time to improve it. Thanks Simon

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ghc static linking on Windows
by Günther Schmidt 02 Jul '09

02 Jul '09

Hi, I tried to compile an app that uses sqlite3.dll with the -optl-static flag and the error message is: C:\ghc\ghc-6.10.3\gcc-lib\ld.exe: cannot find -lsqlite3 collect2: ld returned 1 exit status

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Suggestions for simulating Object ID
by Hemanth Kapila 01 Jul '09

01 Jul '09

Hello all, Can some one please suggest something on simulating some sort of "object-Ids" in Haskell? I mean, something like the following relation will hold: > a1 == a2 = (objectID a1) == (objectID a2) Currently I have something like > import Data.Hash >import qualified Data.ByteString.Char8 as B > newtype UniqueID = UniqueID (Hash, B.ByteString) I have a type class called Identifiable, the instances of which are supposed to give a unqiue bytestring representation of the instance which can be arbitrarily long but should satisfy the condition mentioned earlier. > class Identifiable a where > instanceID :: a -> B.ByteString and finally, the required funtion objectID is defined as : > objectID :: (Hashable a, Identifiable a) => a -> UniqueID > objectID a1 = UniqueID (hash a1, instanceID a1) while comparing object Ids, I compare the hash values first (which can be faster for arbitrary values). Only if they are equal then I compare the instanceIDs and count on laziness for avoiding the construction of the bytestrings where they are not needed. Can you please suggest a better approach? I also toyed with the idea of storing all the data 'objects' in an array and use the index as the identifier but the trouble is I am not aware of all the number of instances before hand under all the circumstances. Many thanks Hemanth K

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Happy GLR mode build failures
by Cetin Sert 01 Jul '09

01 Jul '09

Hi, It's not possible to build the Happy glr examples using GHC 6.10.3 and Happy 1.18.4: cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ make make loop CMD=run make[1]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr' for d in expr-eval expr-tree expr-monad hidden-leftrec highly-ambiguous packing nlp bio-eg; do (cd $d && make run); done make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-eval' # might want to run happy with --ghc ghc -I../common -i../common -package data -O -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-eval' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-tree' # might want to run happy with --ghc ghc -I../common -i../common -package data -O2 -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-tree' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-monad' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-monad' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/hidden-leftrec' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/hidden-leftrec' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/highly-ambiguous' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/highly-ambiguous' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/packing' Makefile:8: warning: overriding commands for target `.y.hs' ../Makefile.defs:15: warning: ignoring old commands for target `.y.hs' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/packing' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/nlp' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o english --make Main.lhs <command line>: unknown package: data make[2]: *** [english] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/nlp' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/bio-eg' Making BioData.hs WITHOUT optimisation (for speed) ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -funfolding-use-threshold0 -fno-strictness -c BioData.hs <command line>: unknown package: data make[2]: *** [BioData.hi] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/bio-eg' make[1]: *** [loop] Error 2 make[1]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr' make: *** [all] Error 2 cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ cabal update Downloading the latest package list from hackage.haskell.org cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ cabal install data cabal: There is no package named data cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ happy --version; ghc --version Happy Version 1.18.4 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c) 1997-2005 Simon Marlow Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY. This program is free software; you can redistribute it and/or modify it under the terms given in the file 'LICENSE' distributed with the Happy sources. The Glorious Glasgow Haskell Compilation System, version 6.10.3 or GHC 6.10.1 and Happy 1.18.2: cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ makemake loop CMD=run make[1]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr' for d in expr-eval expr-tree expr-monad hidden-leftrec highly-ambiguous packing nlp bio-eg; do (cd $d && make run); done make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-eval' # might want to run happy with --ghc ghc -I../common -i../common -package data -O -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-eval' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-tree' # might want to run happy with --ghc ghc -I../common -i../common -package data -O2 -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-tree' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-monad' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-monad' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/hidden-leftrec' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/hidden-leftrec' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/highly-ambiguous' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/highly-ambiguous' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/packing' Makefile:8: Warnung: Die Befehle für das Ziel ».y.hs« werden überschrieben ../Makefile.defs:15: Warnung: Alte Befehle für das Ziel ».y.hs« werden ignoriert ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/packing' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/nlp' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o english --make Main.lhs <command line>: unknown package: data make[2]: *** [english] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/nlp' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/bio-eg' Making BioData.hs WITHOUT optimisation (for speed) ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -funfolding-use-threshold0 -fno-strictness -c BioData.hs <command line>: unknown package: data make[2]: *** [BioData.hi] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/bio-eg' make[1]: *** [loop] Fehler 2 make[1]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr' make: *** [all] Fehler 2 cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ happy --version; ghc --version Happy Version 1.18.2 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c) 1997-2005 Simon Marlow Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY. This program is free software; you can redistribute it and/or modify it under the terms given in the file 'LICENSE' distributed with the Happy sources. The Glorious Glasgow Haskell Compilation System, version 6.10.1 When I try to manually build something out of a .y file, I keep getting: cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ find | grep -E "y$" | xargs -n 1 echo happy -gcal happy -gcal ./packing/Expr.y happy -gcal ./highly-ambiguous/Expr.y happy -gcal ./expr-eval/Expr.y happy -gcal ./expr-monad/Expr.y happy -gcal ./nlp/English.y happy -gcal ./hidden-leftrec/Expr.y happy -gcal ./expr-tree/Expr.y happy -gcal ./bio-eg/Bio.y cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ find | grep -E "y$" | xargs -n 1 happy -gcal reduce/reduce conflicts: 2 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 7 reduce/reduce conflicts: 1 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 9 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 9 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 2 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 4 reduce/reduce conflicts: 1 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 9 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) unused rules: 20 shift/reduce conflicts: 35 reduce/reduce conflicts: 68 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) Does anyone have solution for this? The irrefutable pattern failure issue is especially bothersome for me as I ran into it in a Fortran grammar I'm writing and got stuck. Best Regards, Cetin Sert

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