On 2007-08-28, Davy <[EMAIL PROTECTED]> wrote:
> On Aug 28, 11:00 am, Davy <[EMAIL PROTECTED]> wrote:
>> Hi all,
>>
>> It is well known that Python is appreciated for its merit of concise.
>> However, I found the over concise code is too hard to understand for
>> me.
>>
>> Consider, for instance,
>> def known_edits2(word):
>> return set(e2 for e1 in edits1(word) for e2 in edits1(e1) if e2 in
>> NWORDS)
>>
>> Shall I understand the code in set() as
>> for e2 in edits1(e1) {
>> if e2 in NWORDS {
>> for e1 in edits1(word) {
>> e2
>> }
>> }
>>
>> }
>>
> [SNIP]
> Hi all, I figured it myself. It is left to righ parse, right?
> So the above one is like
> for e1 in edits1(word) {
> for e2 in edits1(e1) {
> if e2 in NWORDS {
> push e2 to set
> }
> }
> }
This is correct, although I am not sure what language you are using here, it
looks like a strange mix of Python and C to me.
>> Any suggestions are welcome!
The idea is known as List comprehension (for lists, obviously), and comes from
functional programming, Bird & Wadler used it in their book.
The notation is very close to mathematics:
{ e2 | e1: edits(word), e2: edits(e1) in NWORDS }
or in LaTeX:
$\{ e_2 | \forall e_1: \mathrm{edits}(\mathrm{words}),
\forall e_2: \mathrm{edits}(e_1) \in \mathrm{NWORDS} \}$
:-)
(which in words is something like: collect values e2, where e1 comes from
'edits(word)', e2 comes from 'edits(e1)', and e2 in NWORDS)
Sincerely,
Albert
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