On Thu, May 16, 2019 at 10:21:14PM -0500, Nathan Bloomfield wrote:

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 ... ```

In fact, and this is veering somewhat off-topic, but I would strongly recommend *not* making a default match `(A1,_)` because then you will get an explicit warning if indeed `Rule2` gets more constructors.

This works, but may not suitable as case. Sometimes it may be hard to name the function just for branching. On Fri, May 17, 2019 at 11:25 AM Vanessa McHale wrote:

For one, you should pattern match rather than using nested ifs, viz.

foo A1 B1 = fun1

Using a case statement on tuples is not necessary.

On 5/17/19 3:12 AM, Magicloud Magiclouds 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? _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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