[Haskell-cafe] How to express a logic matrix clearly?

[Nathan Bloomfield]

This is a good opportunity to use case syntax. You can also case on tuples,
like this:

```
foo a b = case (a,b) of
  (A1,B1) -> fun1
  (A1,B2) -> fun2
  (A1,B3) -> fun3
  (A1,_)  -> fun4   <- this is probably not necessary anymore, unless you
expect Rule2 to get more constructors.
  (A2,B1) -> fun5
  ...
```

On Thu, May 16, 2019 at 10:14 PM Magicloud Magiclouds <
magicloud.magiclouds at gmail.com> wrote:

> Hi,
> I have trouble describing this clearly. Let me show code directly.
>
> data Rule1 = A1 | A2 | A3
> data Rule2 = B1 | B2 | B3
>
> foo a b =
>   if a == A1
>     then if b == B1
>       then fun1
>       else if b == B2
>         then fun2
>         else if b == B3
>           then fun3
>           else fun4
> ...
>
> Basically, Rule1 and Rule2 compose a matrix, for each case of Rule1
> and Rule2, I need to do different things. Above is already long and
> not quite clear, and it is far from complete.
>
> So my question is, is there a way/lib that I can make this clear to
> read/understand?
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-- 
Nathan Bloomfield
Code Wrangler, Team Absinthe
Automattic, Inc.
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