In Haskell, what does it mean if a binding "shadows an existing binding"?

Posted by Alistair on Stack Overflow See other posts from Stack Overflow or by Alistair
Published on 2010-05-25T07:19:30Z Indexed on 2010/05/25 7:21 UTC
Read the original article Hit count: 407

Filed under:

haskell

|

compiler-warnings

|

ghc

I'm getting a warning from GHC when I compile:

Warning: This binding for 'pats' shadows an existing binding in the definition of 'match_ignore_ancs'

Here's the function:

match_ignore_ancs (TextPat _ c) (Text t) = c t
match_ignore_ancs (TextPat _ _) (Element _ _ _) = False
match_ignore_ancs (ElemPat _ _ _) (Text t) = False
match_ignore_ancs (ElemPat _ c pats) (Element t avs xs) =
   c t avs && match_pats pats xs

Any idea what this means and how I can fix it?

Cheers.

© Stack Overflow or respective owner

Related posts about haskell

Learning Haskell: How to remove an item from a List in Haskell

as seen on Stack Overflow - Search for 'Stack Overflow'
Trying to learn Haskell. I am trying to write a simple function to remove a number from a list without using built-in function (delete...I think). For the sake of simplicity, let's assume that the input parameter is an Integer and the list is an Integer list. Here is the code I have, Please tell me… >>> More
Using Data.Heap in Haskell, or reading Haskell docs for a beginner

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to use Haskells Data.Heap module, but I'm incapable of even using it with integers. The only heap I've been capable of using is "empty", which does not take any arguments. Later on I'll figure out how to instance for my needs, but for now I'd be glad if I was even able to test it with… >>> More
What kind of things are easy in Haskell and hard in Scala, and vice versa?

as seen on Programmers - Search for 'Programmers'
There has been some intermingling of Scala and Haskell communities, and I have noticed now and then people commenting on stuff that's supposed to be easy in Haskell and hard and Scala. Less often (maybe because I read Scala questions, not Haskell ones), I see someone mentioning that something in Scala… >>> More
Haskell's cabal dependency problem with happy

as seen on Programmers - Search for 'Programmers'
I have problems installing ghc-mod on my linux machine. cabal worries about "happy" not being available in versione = 1.17: $ cabal install ghc-mod Resolving dependencies... [1 of 1] Compiling Main ( /tmp/haskell-src-exts-1.14.0-1357/haskell-src-exts-1.14.0/Setup.hs, /tmp/haskell-src-exts-1… >>> More
Understanding Haskell's fibonacci

as seen on Stack Overflow - Search for 'Stack Overflow'
fibs :: [Int] fibs = 0 : 1 : [ a + b | (a, b) <- zip fibs (tail fibs)] This generates the Fibonacci sequence. I understand the behaviour of the guards, of :, zip and tail, but I don't understand <-. What is it doing here? >>> More

Related posts about compiler-warnings

Suppressing line specific XCode compiler warnings

as seen on Stack Overflow - Search for 'Stack Overflow'
Similar to Ben Gottlieb's question, I have a handful of deprecated calls that are bugging me. Is there a way to suppress warnings by line? For instance: if([[UIApplication sharedApplication] respondsToSelector:@selector(setStatusBarHidden:withAnimation:)]) { [[UIApplication sharedApplication]… >>> More
g++ C++0x enum class Compiler Warnings

as seen on Stack Overflow - Search for 'Stack Overflow'
I've been refactoring my horrible mess of C++ type-safe psuedo-enums to the new C++0x type-safe enums because they're way more readable. Anyway, I use them in exported classes, so I explicitly mark them to be exported: enum class __attribute__((visibility("default"))) MyEnum : unsigned int { … >>> More
Visualize compiler warnings

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm looking for a way to visualize compiler warnings and remarks, by annotating or otherwise showing which lines cause a report. This is much like a modern IDE like NetBeans or Eclipse already does, but I'd like to take output from several compilers (and other static code analysis tools) at once… >>> More
G++, compiler warnings, c++ templates

as seen on Stack Overflow - Search for 'Stack Overflow'
During the compilatiion of the C++ program those warnings appeared: c:/MinGW/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bc:/MinGW/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stl_algo.h:2317: instantiated from `void std::partial_sort(_RandomAccessIterator, _RandomAccessIterator… >>> More
CSharpCodeProvider doesn't return compiler warnings when there are no errors

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm using the CSharpCodeProvider class to compile a C# script which I use as a DSL in my application. When there are warnings but no errors, the Errors property of the resulting CompilerResults instance contains no items. But when I introduce an error, the warnings suddenly get listed in the Errors… >>> More