From: Dave Burt <dave@...>
Date: 2006-10-09T10:55:11+09:00
Subject: Re: || explanation in ruby... in pseudolanguage

Tuka Opaleye wrote:
> I am trying to get my head around the || symbol used extensively in
> ruby. To me it is somewhat foreign still and I am trying a few exercise
> to make it click. Can anyone suggest a phrase (pseudolanguage) that
> accurately expresses the possible expressions using || ?
> 
> input.each_byte do |b|
>   case b
>     ...
>   end
> for each byte in input, assign it to b...

You're right, assignment is correct. Imagine a special variable
yielded_values; the block could be expressed like this:

do
  b = *yielded_values
  case b
    ...
  end
end

Implicit in this is that you can use full assignment semantics, as in
this idiom:

my_hash.inject(initial_value) do |memo, (key, value)|
  ...
end

It works this way: inject yields a [memo, whatever_each_yields] pair,
and Hash#each yields a [key, value] pair. This is the analogous assignment:

yielded_values = [:memo, [:key, :value]]
memo, (key, value) = *yielded_values

How would you say this in English? Inject is problematic this way; I
don't understand how to explain it naturally using the word "inject" at
all. But perhaps you could use a general form such as "call inject with
the parameter initial_value and a block taking parameters memo, key and
value."

> Ex 2:
> open('smiley.html', 'wb') do |f|
>   f << ...
> end
> 
> Sugestions ?.....

*With* an open binary-write mode file handle to "smiley.html" *as* f...

What a block means depends on the method. You've looked at iteration and
scope-of-an-opened-object examples, which are probably the most common,
but there are others (e.g. Markaby).

Cheers,
Dave