RHG
本日はRHGのふつける読書会にきています。
今回のモナドからです。
以下メモ
x >>= f = concatMap f xs
[x] >>= f
concatMap f [x] -> map [f x]
[x] >>= f
concatMap f [x]
concat (map f [x])
[f x] -> f [(1,2)] -> []
IOモナドのところで評価と実行は違うということが話題になりました。
f:: (x,w) -> (b,w) f:: a -> (w -> (b,w))
main = do <-getStdGen let ns = take 3 (randoms g) print (ns::[Int])
は次の二つのように書き換えられる
getStdGen >>= \g -> print (take 3 (radoms g))
getStddGen >>= rndoms >>> take 3 >>> put
ポイントフリースタイルの書き換え
f . g = \ x -> (g x) f . g = \ x -> g (f x)
本日はSICP読書会
書いたソースとか
(define (count-leaves tree) (fold + 0 (map (lambda (x) (if (pair? x) (count-leaves x) 1)) tree))) (define (sum seq) (fold + 0 seq)) (define (dot-product v w) (sum (map * v w))) (define (transpose mat) (fold-right (lambda (first rest) (if (null? rest) (map list first) (map cons first rest))) '() mat)) (define (matrix-*-vect mat vec) (map (lambda (m) (dot-product m vec)) mat)) (define (matrix-*-matrix mat1 mat2) (map (lambda m1 (map dot-product m1 (transpose mat2))) mat1)) (define (matrix-+-matrix mat1 mat2) (map (lambda (x y) (map + x y)) mat1 mat2)) (define (reverse seq) (fold-right (lambda (x y) (append y (list x))) '() seq)) (define (reverse seq) (fold-left (lambda (x y) (cons x y)) '() seq))
Cleanでコッホ曲線
書いたよ。
以下そーす
Start world # testwindow = Window "TestDraw" NilLS [WindowClose (noLS closeProcess) ,WindowViewSize size ,WindowLook True (\_ _ -> example6) ,WindowViewDomain { corner1=origin,corner2=maxdomain } ] = startIO SDI Void (snd o openWindow undef testwindow) [ProcessClose closeProcess] world where size = { w=500, h=500 } origin = zero maxdomain = { x=origin.x+size.w, y=origin.y+size.h } example6 = fst o (coch 4 {x=0,y=200} 500.0 0.0) coch :: Int Point2 Real Real *Picture -> (*Picture,Point2) coch level point len degree pic | level == 0 = let point` = (nextPoint point len degree) in ((drawLine point point` pic), point`) | otherwise // # (pic,point) = coch (level-1) point len` degree pic # degree = degree+60.0 # (pic,point) = coch (level-1) point len` degree pic # degree = degree+240.0 # (pic,point) = coch (level-1) point len` degree pic # degree = degree+60.0 = coch (level-1) point len` degree pic where nextPoint current l deg = {x=x2,y=y2} where // 最初この関数が悪さを… entier x2 = point.x + toInt (l * cos (toRadian (toReal deg))) y2 = point.y + toInt (l * sin (toRadian (toReal deg))) len` = len / 3.0 toRadian :: Real -> Real toRadian a = a * PI / 180.0 toDegree :: Real -> Real toDegree a = a * 180.0 / PI
おまけ
"koichi"から"i"を除くと"koch"になるどうでもいいことに気づいてしまった…
以下Haskell
filter (not . (== 'i')) "koichi"
GRS
グラフ書き換え理論って必然的に"Call by name"になるの?