[Haskell-cafe] Is it possible to declare assignment operators in Haskell?

Joe Quinn headprogrammingczar at gmail.com
Wed Feb 5 21:52:31 UTC 2014

On 2/5/2014 7:37 AM, Alexander Alexeev wrote:
> Hello!
> I'm wondering, is there any way to declare assignment operators
> in Haskell? For example, strict assignment operators:
> x .= y -- equals: let x = y `deepseq` y
> x := y -- equals: x <- y `deepseq` y
> As far as I can tell, Template Haskell is not able to do anything like
> this, because I can't event quote expressions like `let x = y` or `x <-
> y`. Is there any other way (plugin for GHC, etc)? Or maybe I'm doing
> something wrong and TH is quite able to handle this task?
> I'm pretty sure that I could use a preprocessor, but I wonted to find
> a better solution.
There are things that "act like assignment", but quite differently than 
what you are after, which looks like a macro of some sort.
For instance, one of the OpenGL packages defines (:=) = writeIORef, to 
be used like

spoofel depth stencil = do
   stencilVals <- map (> 0.35) <$> readIORef depth
   stencil := stencilVals

What is the type of (.=) and (:=) that you desire? What is the larger 
problem you are trying to solve?

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