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An interesting demonstration of why closures are useful is to start from a hypothetical language that supports closures but not objects and then implement a (si

An interesting demonstration of why closures are useful is to start from a hypothetical language that supports closures but not objects and then implement a (simple!) object/class system. For me, it was extremely clarifying to have something in my mind click and go "Oh, OOP doesn't need to be a language feature ... there's this much more powerful concept available as a building block."

slmbrhrt 17y ago
The venerable master Qc Na was walking with his student, Anton. Hoping to prompt the master into a discussion, Anton said "Master, I have heard that objects are a very good thing - is this true?" Qc Na looked pityingly at his student and replied, "Foolish pupil - objects are merely a poor man's closures." Chastised, Anton took his leave from his master and returned to his cell, intent on studying closures. He carefully read the entire "Lambda: The Ultimate..." series of papers and its cousins, and implemented a small Scheme interpreter with a closure-based object system. He learned much, and looked forward to informing his master of his progress. On his next walk with Qc Na, Anton attempted to impress his master by saying "Master, I have diligently studied the matter, and now understand that objects are truly a poor man's closures." Qc Na responded by hitting Anton with his stick, saying "When will you learn? Closures are a poor man's object." At that moment, Anton became enlightened.
- deleted 17y ago
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- jriddycuz 17y ago
  You have much to teach us, great one.
- jamesbritt 17y ago
  No link to the source? http://people.csail.mit.edu/gregs/ll1-discuss-archive-html/msg03277.html http://people.csail.mit.edu/gregs/ll1-discuss-archive-html/m...
tamas 17y ago
The idea is really nice, but I'm not sure it would work on the OP's Joe, who probably wouldn't even care about the hypothetical language and would regard the whole concept hypothetical, only for those who have way too much free time. (With WoW on the table, you don't have that luxury.) I would take the route of first order functions -> anonymous functions -> closures, but I think it is really a lost cause for the typical 9-5 programmers.
- gruseom 17y ago
  I would take the route of first order functions -> anonymous functions -> closures But those are three completely different concepts. A closure need not be anonymous or even first-order.
gcv 17y ago
Yes. This approach works. I used it when I actually did work in a proprietary language which had no usable objects, but did have half-decent lambdas. Most people did not understand or use them at all, but one new guy with a Java background asked me how to cope. I explained to him how to use closures to implement a simple bank account class, and he got it immediately. I don't think this guy played WoW, though. :)
wingo 17y ago
You still want applicable objects, though, and closures don't quite cut it. (I say this as a schemer.) See http://www.r6rs.org/formal-comments/comment-6.txt http://www.r6rs.org/formal-comments/comment-6.txt, for example.

slmbrhrt 17y ago

The venerable master Qc Na was walking with his student, Anton. Hoping to prompt the master into a discussion, Anton said "Master, I have heard that objects are a very good thing - is this true?" Qc Na looked pityingly at his student and replied, "Foolish pupil - objects are merely a poor man's closures." Chastised, Anton took his leave from his master and returned to his cell, intent on studying closures. He carefully read the entire "Lambda: The Ultimate..." series of papers and its cousins, and implemented a small Scheme interpreter with a closure-based object system. He learned much, and looked forward to informing his master of his progress. On his next walk with Qc Na, Anton attempted to impress his master by saying "Master, I have diligently studied the matter, and now understand that objects are truly a poor man's closures." Qc Na responded by hitting Anton with his stick, saying "When will you learn? Closures are a poor man's object." At that moment, Anton became enlightened.

deleted 17y ago
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jriddycuz 17y ago
You have much to teach us, great one.
jamesbritt 17y ago
No link to the source? http://people.csail.mit.edu/gregs/ll1-discuss-archive-html/msg03277.html http://people.csail.mit.edu/gregs/ll1-discuss-archive-html/m...

tamas 17y ago

The idea is really nice, but I'm not sure it would work on the OP's Joe, who probably wouldn't even care about the hypothetical language and would regard the whole concept hypothetical, only for those who have way too much free time. (With WoW on the table, you don't have that luxury.) I would take the route of first order functions -> anonymous functions -> closures, but I think it is really a lost cause for the typical 9-5 programmers.

gruseom 17y ago
I would take the route of first order functions -> anonymous functions -> closures But those are three completely different concepts. A closure need not be anonymous or even first-order.

gcv 17y ago

Yes. This approach works. I used it when I actually did work in a proprietary language which had no usable objects, but did have half-decent lambdas. Most people did not understand or use them at all, but one new guy with a Java background asked me how to cope. I explained to him how to use closures to implement a simple bank account class, and he got it immediately. I don't think this guy played WoW, though. :)

wingo 17y ago

You still want applicable objects, though, and closures don't quite cut it. (I say this as a schemer.) See http://www.r6rs.org/formal-comments/comment-6.txt http://www.r6rs.org/formal-comments/comment-6.txt, for example.