Re: [elm-discuss] Re: pattern matching on a field within a record

[Martin DeMello]

On Sat, Sep 24, 2016 at 9:11 PM, Nick H  wrote:

>
> Regarding null_square: If you want to make sure that null_square is passed
> by reference, you can define it as a top-level value. (That said, the
> record is so small, I doubt it would make a noticeable performance
> difference, unless you're planning on making a gazillion of them.)
>

That's what I ended up doing, and the code was pretty nice with it.

martin

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Re: [elm-discuss] Re: pattern matching on a field within a record

[Nick H]

Re: your initial post... you could rewrite the code as

case Maybe.map .cell c of
  Just (Letter s) ->
s
  _ ->
""

Don't know if that's any easier to read, though.

Regarding null_square: If you want to make sure that null_square is passed
by reference, you can define it as a top-level value. (That said, the
record is so small, I doubt it would make a noticeable performance
difference, unless you're planning on making a gazillion of them.)


On Sat, Sep 24, 2016 at 1:44 PM, Martin DeMello 
wrote:

> Don't think that will work because c is of type Maybe Square, not Maybe
> Cell.
>
> One further question - if I define
>
> let null_square = { cell = Empty, num = 0 }
>
> let get_square maybe_square =
>   case maybe_cell of
> Nothing: null_square
> Just s : s
>
> let get_letter maybe_square =
>   case maybe_square of
> { Letter s } -> s
> _ -> ""
>
> would that be introducing an inefficient creation of a null_square every
> time I call get_letter or is it just a cheap reference?
>
> martin
>
> On Fri, Sep 23, 2016 at 12:04 PM, Simon  wrote:
>
>> This should work
>>
>>  case c of
>> Just (Letter s) ->
>>   s
>> _ -> ""
>>
>>
>>
>> On Friday, 23 September 2016 03:50:19 UTC+2, Martin DeMello wrote:
>>>
>>> If I have the following code:
>>>
>>> type Cell = Empty | Letter String
>>>
>>> type alias Square =
>>>   { cell : Cell
>>>   , num : Int
>>>   }
>>>
>>> and c : Maybe Square,
>>>
>>> can I do the following in a single match?
>>>
>>>   case c of
>>> Just { cell } ->
>>>   case cell of
>>> Letter s -> s
>>> _ -> ""
>>> _ -> ""
>>>
>>> that is, i conceptually want
>>>
>>>   case c of
>>> Just { cell = Letter s } -> s
>>> _ -> ""
>>>
>>> martin
>>>
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Re: [elm-discuss] Re: pattern matching on a field within a record

[Martin DeMello]

Don't think that will work because c is of type Maybe Square, not Maybe
Cell.

One further question - if I define

let null_square = { cell = Empty, num = 0 }

let get_square maybe_square =
  case maybe_cell of
Nothing: null_square
Just s : s

let get_letter maybe_square =
  case maybe_square of
{ Letter s } -> s
_ -> ""

would that be introducing an inefficient creation of a null_square every
time I call get_letter or is it just a cheap reference?

martin

On Fri, Sep 23, 2016 at 12:04 PM, Simon  wrote:

> This should work
>
>  case c of
> Just (Letter s) ->
>   s
> _ -> ""
>
>
>
> On Friday, 23 September 2016 03:50:19 UTC+2, Martin DeMello wrote:
>>
>> If I have the following code:
>>
>> type Cell = Empty | Letter String
>>
>> type alias Square =
>>   { cell : Cell
>>   , num : Int
>>   }
>>
>> and c : Maybe Square,
>>
>> can I do the following in a single match?
>>
>>   case c of
>> Just { cell } ->
>>   case cell of
>> Letter s -> s
>> _ -> ""
>> _ -> ""
>>
>> that is, i conceptually want
>>
>>   case c of
>> Just { cell = Letter s } -> s
>> _ -> ""
>>
>> martin
>>
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