'git add -p'

Hi, it is NISHIO Hirokazu. I just found "git add -p" is very nice. I show it.

Here is a sample script. I'm going to add new function on it.

def hallo():
    print "hello!"

When I added new function 'bye', I also found there is a typo s/hallo/hello/. I fixed it too. Let me show 'git diff'

$ git diff
@@ -1,2 +1,5 @@
-def hallo():
+def hello():
     print "hello!"
+
+def bye():
+    print "bye!!"

Now I wanted to commit it, but there are two changesets. I didn't want to commit all in one changeset. That's when I should use 'git add -p'!

$ git add -p
@@ -1,2 +1,5 @@
-def hallo():
+def hello():
     print "hello!"
+
+def bye():
+    print "bye!!"
Stage this hunk [y,n,q,a,d,/,s,e,?]? 

Git asked me whether choose the block of changes (hunk). But it contains both changes... I chose 's' to split it.

Stage this hunk [y,n,q,a,d,/,j,J,g,e,?]? s
Split into 2 hunks.
@@ -1,2 +1,2 @@
-def hallo():
+def hello():
     print "hello!"
Stage this hunk [y,n,q,a,d,/,j,J,g,e,?]?

Now I pressed 'y' to choose the hunk, 'n' to skip another hunk and commit.

Stage this hunk [y,n,q,a,d,/,j,J,g,e,?]? y
@@ -2 +2,4 @@
     print "hello!"
+
+def bye():
+    print "bye!!"
Stage this hunk [y,n,q,a,d,/,K,g,e,?]? n

$ git commit -m "fix typo"
[master 82bd7c6] fix typo
 1 files changed, 1 insertions(+), 1 deletions(-)

Let me show 'git diff' again. The other modification left. Add it and commit it.

$ git diff
@@ -1,2 +1,5 @@
 def hello():
     print "hello!"
+
+def bye():
+    print "bye!!"

$ git add .
$ git commit -m "add new function: 'bye'"
[master fd5ab40] add new function: 'bye'
 1 files changed, 3 insertions(+), 0 deletions(-)

How nice is it! Does other VCS (mercurial, subversion etc.) has such feature?

What is 4277075694

Hi, it is NISHIO Hirokazu. I encountered the magic number, 4277075694, when I hacked on Windows. I searched where it comes from. However, it doesn't appear on any code. I also searched 0xFEEEFEEE, 0xFEEE and 65262, and it neither.

Finally I found: 4277075694 (0xFEEEFEEE) comes from Windows NT's heap manager. When a memory released, it is set to 0xFEEEFEEE.

Here are other magic numbers:

0xBAADF00D : 3131961357
0xFDFDFDFD : 4261281277
0xCDCDCDCD : 3452816845
0xDDDDDDDD : 3722304989
0xFEEEFEEE : 4277075694

Here is good instruction: Win32 Debug CRT Heap Internals

The shortest oneline brainf*ck interpreter in python (558 characters)

Hi, it is Dr. NISHIO Hirokazu. This code was written in 2006-09 but I didn't have publish yet in English.

get from here: http://gist.github.com/476940. It takes a filename as an argument and exec it as Brainf*ck code. All illegal characters are ignored.

exec(reduce(lambda x,y:x.replace(y[0],y[1:]),'Iz"d",|Jz"t",|K1),"|L.read(|Mimport |O,lambda|Psys.std|Q",0);z"|R"Yzp,|S}.get(code[|T)or |U"YZor z"p",p|Vifilter(bool,(|W)%256)or Z,"|X)for x in count())).next()|Y:lambda:|Zz"c",c+1)|q(globals().get(p,0)|zglobals().__setitem__('.split('|'),'Msys;from itertools Mcount,ifilter;z"cQpQj"O kYq==0)^(k==-1)and(Jc+kTI1TVId+{"]":-1,"[":1St],0)*kTd==0 or Jt+kXand z"c",t+1T1TZ);z"code",file(sys.argv[1])L));Vc==len(code)or({">U+K<U-K+Rq+1W-Rq+255W."YPout.write(chrq)TZ,",Rord(PinL1)W[":j(K]":j(-1),Sc]O:Z)()and NoneX'))

See this charm point!

>U+K<U-K+Rq+1W-Rq+255W

It's a definition of >, <, + and - !

Haskell Quiz Answer

Hi, it is Dr. NISHIO Hirokazu. This is an answer for Haskell Quiz. Please read it in advance.

Why some program show strange behavior? To answer the question, I should define what is "strange". For example the following behavior is strange.

// JS
var a = ***, b = ***, c = ***;
console.log(a < b); // true
console.log(b < c); // true
console.log(c < a); // true

In the case, "strange" means "different from mathematical behavior". Now the answer is clear, it is because those are not purely mathematical objects.

var a = "9", b = 10, c = "100";
console.log(a < b); // true
console.log(b < c); // true
console.log(c < a); // true

Haskell also shares some common "strangeness" with other languages.

Prelude> let x = *****
Prelude> x == x + 1
True

You may know the quiz in the other language. This "strangeness" come from the limited resolution of floating point number.

Prelude> let x = 2 ** 64
Prelude> x == x + 1
True

Now, return to the problem I posted.

In Haskell, you can overload different value on one name.
You may disagree. You may see "Multiple declarations of something" error.
But wait. Didn't you have ever defined 'show'? Isn't it overloaded?

Haskell is very different from C++/Java. In C++/Java, you can overload functions whose type of arguments are different. In Haskell, you can also overload functions whose type of return value are different. It is very important.

The quiz's tricks are,

1. You can overload in Haskell
   
2. You can overload functions whose return value are different
   
3. and there are no need to take argument
   
4. (+) and (==) are t -> t -> t, so it can be used to restrict arguments' type. x + (1::Int) says x is (x::Int).
   
5. Number Literal (e.g. 0) are (Num a) => a, so it can be used as both (0::Int) and (0::Integer).
   

Now let me show my answer.

class Foo t where
    a :: t
    b :: t

instance Foo Int where
    a = 0
    b = 1

instance Foo Integer where
    a = 1
    b = 0

c :: Int
c = 0

d :: Integer
d = 0

main = do
  print $ a + c == 0 -- True.
  print $ a == c     -- True. a::Int == c::Int == 0.
  print $ c == 0     -- True. 
  print $ a + d == 1 -- True. 
  -- d is Integer. So the variable a is a::Integer, 
  -- which equals 1. "d == 1" is a misconception.
  print $ b + c == 1 -- True. b::Int is 1.
  print $ b + d == 0 -- True. However, b::Integer is 0.
  print $ b == d     -- True. Yes, both are 0::Integer;
  print $ d == 0     -- True. 
  -- Why I use "d == 0" not "b == 0"? 
  -- Because it causes "ambiguous type" error.
  -- You know, ":t 0" is "(Num t) => t". No way to determine
  -- it is Int or Integer.

  -- hints to make answer unique (perhaps...)
  print $ sum([a, b, c])  -- 1: It is [0, 1, 0]::[Int]
  print $ sum([a, b, d])  -- 1: It is [1, 0, 0]::[Integer]
  print $ [a, b, c] !! a  -- 0: (!!) take Int argument,
  print $ [a, b, c] !! b  -- 1: so it says (a::Int /= b::Int)
  print $ [a, b, c] !! c  -- 0
  -- Why I didn't show [a, b, c] !! d is, 
  -- it causes error because d is Integer.

Real Point-free Haskell Program

Hi, it is NISHIO Hirokazu. I'm trying to make *REAL* point-free Haskell program. In other words, I want to make point-free (arguments-less) Haskell code with any point(.)

You may know, usually most of Haskell programmer use (.) operator to combine functions. However, it is not necessary. It can replace with (<*>) and const.

Prelude Control.Applicative> :t (.)
(.) :: (b -> c) -> (a -> b) -> a -> c
Prelude Control.Applicative> :t \x y z -> (const x <*> y) z
\x y z -> (const x <*> y) z :: (a -> b) -> (b1 -> a) -> b1 -> b

So anytime you want to use (.) operator, you can do it without (.)

Prelude Control.Applicative> (map . (+)) 1 [1, 2, 3]
[2,3,4]
Prelude Control.Applicative> (const map <*> (+)) 1 [1, 2, 3]
[2,3,4]

And it is also easy to remove points from float expression:

Prelude> 1.5
1.5
Prelude> 15e-1
1.5

The most biggest problem is how to remove this point.

import Control.Applicative
              ^

Haskell Quiz

Hi, it is Dr. NISHIO Hirokazu. Today I made a quiz. See following code and answer the definitions of a, b, c and d.

main = do
  print $ a + c == 0 -- True.
  print $ a == c     -- True. a == c == 0.
  print $ c == 0     -- True. Of course.
  print $ a + d == 1 -- True. d == 1.
  print $ b + c == 1 -- True. b == 1.
  print $ b + d == 0 -- True. What happened?!
  print $ b == d     -- True. ?!
  print $ d == 0     -- True. ?!?!
  -- hints to make answer unique (perhaps...)
  print $ sum([a, b, c])  -- 1
  print $ sum([a, b, d])  -- 1
  print $ [a, b, c] !! a  -- 0
  print $ [a, b, c] !! b  -- 1
  print $ [a, b, c] !! c  -- 0

I swear:

• I didn't define (+)
  
• I didn't define (!!)
  
• I didn't define (==)
  
• I didn't define sum
  
• I didn't define print
  
• I didn't define ($) -- @kmizu sent me a valid solution and he defined ($). I didn't.
  
• I didn't use default -- @camlspotter said it may use defaulting, and I didn't know it. I agree with him that it would be easier if I used defaulting. But I didn't. I didn't use default defaulting (i.e. default ordering of Integer and Double) For more detail, see http://www.haskell.org/onlinereport/decls.html#sect4.3.4
  

All of them are original, came from the prelude module.

The answer will be published on the blog at least 1 week after.

PONG-like game played on iPad with tangible controller

Hi, it is NISHIO Hirokazu. Today I introduce my recent demo movie of Muroto system. Using MUROTO you can controll games on iPad with tangible figures. There are "Muroto device" under the figures. And "Muroto library" tells the type of figures you put on iPhone, the direction and position.

It's not jail-braked. See further information on http://www.nishiohirokazu.org/muroto/