Universal Quantification, Bound and Existential Quantification

Universal quantification is usually not very useful. Inside the body of a universal quantified function, what you know about the argument is very general, because the argument can be *any* type. Suppose you're writing a function with type *->Int, what do you think the function can do? The only implementation I can think of is a constant function:

(pseudo codes)

  f1 :: [forall a] a -> Int
  f1 x = 1

In contrast, existential quantified functions are very useful, because there're always *some* types can do certain things. Use the same example:

  f2 :: [exist a] a -> Int
  f2 x = length x

I can do nearly anything inside f2, because there's always some x will satify the operations applied on them.

You should notice that only functions or Bottom can have universal quantified type.

Bound helps universal quantification a lot. When you give a bound to universal quantification, you give it extra informations.

Ruby 1.8.7 and openssl 1.0.0

Archlinux upgrade openssl from 0.9.8 to 1.0.0 recently, which caused a big headache for me: all ruby distributions, except the latest ruby source code in svn, failed to compile with the new openssl, e.g. (compile error of 1.8.7):

ossl_ssl.c: In function ?ossl_sslctx_get_ciphers?:

ossl_ssl.c:626:19: error: ?STACK? undeclared (first use in this function)

ossl_ssl.c:626:19: note: each undeclared identifier is reported only once for each function it appears in

ossl_ssl.c:626:25: error: expected expression before ?)? token

ossl_ssl.c:629:47: error: expected expression before ?)? token

ossl_ssl.c:629:47: error: too few arguments to function ?sk_value?

/usr/include/openssl/stack.h:80:7: note: declared here

ossl_ssl.c: In function ?ossl_ssl_get_peer_cert_chain?:

ossl_ssl.c:1199:5: warning: passing argument 1 of ?sk_num? from incompatible pointer type

/usr/include/openssl/stack.h:79:5: note: expected ?const struct _STACK *? but argument is of type ?struct stack_st_X509 *?

ossl_ssl.c:1202:2: warning: passing argument 1 of ?sk_value? from incompatible pointer type

/usr/include/openssl/stack.h:80:7: note: expected ?const struct _STACK *? but argument is of type ?struct stack_st_X509 *?

ossl_ssl.c: In function ?ossl_ssl_get_cipher?:

ossl_ssl.c:1224:12: warning: assignment discards qualifiers from pointer target type

make[1]: *** [ossl_ssl.o] Error 1

make: *** [all] Error 1

Here's a patch for 1.8.7, it's a modified version of this. Copy and save it as openssl.patch in 1.8.7 source directory, run 'patch -p0 < openssl.patch' and recompile, there should be no errors anymore.

GoF's refactoring draft of the old 23 design patterns

* Interpreter and Flyweight should be moved into a separate category that we referred to as "Other/Compound" since they really are different beasts than the other patterns. Factory Method would be generalized to Factory.

* The categories are: Core, Creational, Peripheral and Other. The intent here is to emphasize the important patterns and to separate them from the less frequently used ones.

* The new members are: Null Object, Type Object, Dependency Injection, and Extension Object/Interface (see "Extension Object" in Pattern Languages of Program Design 3, Addison- Wesley, 1997).

* These were the categories:
  + Core: Composite, Strategy, State, Command, Iterator, Proxy, Template Method, Facade
  + Creational: Factory, Prototype, Builder, Dependency Injection
  + Peripheral: Abstract Factory, Visitor, Decorator, Mediator, Type Object, Null Object, Extension Object
  + Other: Flyweight, Interpreter

via

[ANN] Rubytest.vim 1.0.0 Released

Rubytest.vim is a vim (http://www.vim.org) plugin, which helps you to run tests/specs/features in vim, in order to accelerate your red-green development circle.

Within this realease, rubytest.vim supports almost all popular TDD/BDD frameworks in ruby community: testunit, rspec, shoulda, cucumber ...

Happy hacking!

Changelog
---------

* Support cucumber features
* Support rspec drb mode
* Serveral bug fixes

Get it here: http://www.vim.org/scripts/script.php?script_id=2612

TokyoTyrant vs MongoDB vs CouchDB, simple benchmarks

Jeffery Zhao published a simple benchmark of 2 'NoSQL' databases recently. In that article only basic CRU operations are compared. On macbook unibody+osx, which is the platform Jeff use, MongoDB got slightly better scores than TokyoTyrant on almost every aspect.

We're very interested in CouchDB these days, so I cloned Jeff's benchmark suite, added scripts for CouchDB, and ran the benchmark on my platform, macbook unibody+archlinux again. However the result is really interesting - it's totally the opposite - TokyoTyrant is much more faster than MongoDB on my box.

Results:


CouchDB is really slow compared to TT or MongoDB, so I just give up it after serveral round.

The only difference between Jeff's and mine platform seems operating system: he use OSX while I use linux. I'm not sure whether this is the reason we get different results, or because TT is well optimized by gcc on linux?

Try it yourself: Simple NoSQL Bench (The suite is written in Ruby)

update: After changed from Net::HTTP to Curb, couchdb benchmarks improved about 1/3. Config couchdb [uuids] algorithm to sequential (in default.ini) has no effect on result. All 3 drivers connect to database through network, but only couchdb use http protocol, this is a bottleneck, or, trade off.

Not Invented Here

'In programming, it is also common to refer to the NIH Syndrome as the tendency towards reinventing the wheel (reimplementing something that is already available) based on the flawed belief that in-house developments are inherently better suited, more secure or more controlled than existing implementations. This argument is accepted as flawed because wide usage is much more likely to uncover any existing defects than reimplementation. Even more, peer review of source code in the case of a Free Software or Open Source alternative tends to follow Linus' Law: "given enough eyeballs, all bugs are shallow"'

Not Invented Here

Patent System

HungryHobo's comment on /.:

Without patents:

1: I write some nice software and sell it.
2a: I make a little money, not enough to quit my day job.
2b: I don't make money, all I've lost is time.

With patents:

1: I try to research previous patents, they're almost unreadable..... I have no money to hire a patent lawyer(barrier to entry one)... so I can't be certain if my idea has already been patented.
2a: I stop for fear of infringing on someones patent and being sued into the ground.(barrier to entry 2)
2b: I keep going and write my app... it might be infringing but I don't think it is....
3a: I make a little money.
3b: I make no money.
4: Someone sues me.
5a: It is infringing- well they pull out records that yes I did view their patent in the course of my research in step 1 and obviously stole their idea. They get tripple damages I lose my house. (barrier to entry 3)
5b: It is not infringing - so what. I don't have the money for a good lawyer, they win I lose my house.(barrier to entry 4)
5c: It is not infringing - by some miracle I win.... I'm still left with a pile of legal bills and I lose my house.(barrier to entry 5)

In theory the patent system could help me by letting me be just like the guys who sue in the above but I don't have the thousands of dollars it takes to get a patent through nor the time.