Re: E Style

On Sun, Dec 5, 2010 at 12:23 PM, Bill Frantz <[email protected]> wrote:

> In trying to write an E program (to actually do something useful
> to me), I noted the apparent lack of the C construct:
>
>   (bool ? true_value : false_value)
>
> What I have working now is:
>
>   def location := ( if (filename =~ `@{x}Cave@{y}`)   { 0 }
> else if \
>                        (filename =~ `@{x}Frosty@{y}`) { 1 }
> else if \
>                        (filename =~ `@{x}TTT@{y}`)    { 2 }
> else    \
>                        { -1 })
>   if (location == -1) {throw(`ERROR: Filename "$filename"
> yields $location for offset`)}
>
> (The backslashes seem to be needed.)
>

I like Thomas' switch suggestion better than the chained if. But just to
show how to avoid the backslashes, I might format your original as:

  def location := ( if (filename =~ `@{x}Cave@{y}`)   {
      0
  } else if (filename =~ `@{x}Frosty@{y}`) {
      1
  } else if (filename =~ `@{x}TTT@{y}`)    {
      2
  } else { -1 })

or possibly

  def location := ( if (filename =~ `@{x}Cave@{y}`)   {
      0 } else if (filename =~ `@{x}Frosty@{y}`) {
      1 } else if (filename =~ `@{x}TTT@{y}`)    {
      2 } else { -1 })

or

  def location := ( if (filename =~ `@{x}Cave@{y}`)   { 0
  } else if (filename =~ `@{x}Frosty@{y}`) { 1
  } else if (filename =~ `@{x}TTT@{y}`)    { 2
  } else { -1 })

Of these, I'd prefer the first even though it's wasteful of vertical space.


>
> Is there a cleaner way to code this fragment?
>

Independent of chained ifs vs switches, since you are not using the portions
of the specimen matched against the variables in the patterns, I would use
@{_} in the patterns for clarity (and btw an extra smidgen of efficiency).
In E, "_" is the ignore pattern -- matches everything and binds nothing.



>
> Cheers - Bill
>
> -----------------------------------------------------------------------
> Bill Frantz        | I like the farmers' market   | Periwinkle
> (408)356-8506      | because I can get fruits and | 16345
> Englewood Ave
> www.pwpconsult.com | vegetables without stickers. | Los Gatos,
> CA 95032
>
>
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-- 
    Cheers,
    --MarkM

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