The do notation in this instance yields a nice advantage: if you want to switch to a different monad to encapsulate failure you will meely need to swap out the type signature and your function will need no further work. On Aug 4, 2012 7:35 AM, "Matthew" wrote:

I'm a somewhat experienced coder but I am relatively new to Haskell. I've got a question about whether a usage of do notation is idiomatic, or whether it's better to use pattern matching.

I've got two functions which take an input and return Maybe SomeType. If either returns Nothing, I also want to return Nothing. If they both return something, then I'll return something unrelated.

With do notation, I can write something like this:

do foo <- callFoo x bar <- callBar x return (baz)

Alternatively, there's a straightforward pattern match. After binding foo, bar in a couple of where clauses:

case (foo,bar) of (Just x, Just y) -> baz _ -> Nothing

So which approach is more idiomatic, do you think?

Thanks, - Matthew

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On Fri, Aug 3, 2012 at 11:34 PM, Matthew wrote:

I'm a somewhat experienced coder but I am relatively new to Haskell. I've got a question about whether a usage of do notation is idiomatic, or whether it's better to use pattern matching.

I've got two functions which take an input and return Maybe SomeType. If either returns Nothing, I also want to return Nothing. If they both return something, then I'll return something unrelated.

With do notation, I can write something like this:

do foo <- callFoo x bar <- callBar x return (baz)

Alternatively, there's a straightforward pattern match. After binding foo, bar in a couple of where clauses:

case (foo,bar) of (Just x, Just y) -> baz _ -> Nothing

So which approach is more idiomatic, do you think?

The short answer is to write a "one liner" using (>>=) and (>>), unless you need to bind more than one value to a variable. In that case, you should use an applicative interface, if available and otherwise possible, and finally do-notation.