Adding Pluggable Search Strategies to Your Favourite Functional Programming Language

search3 :: !Bool !(u:a -> .(v:([u:a] -> w:[.b]) -> x:[.b])) u:a -> y:[.b], [v <= u,x v <= w,x v <= y]
search3 kind explorer root
 | kind = do_all_depth [root] []
 = do_all_breadth [root] []
where
 do_all_depth [] t = t
 do_all_depth [v:vs] t = explorer v \ vs` = do_all_depth vs` (do_all_depth vs t)
    
 do_all_breadth [] t = t
 do_all_breadth [v:vs] t = explorer v \ vs` = do_all_breadth vs (do_all_breadth vs` t)

Purely Functional Queue with Constant Operation Times (Credits to Okasaki)

:: Queue a = Queue !Int !.[a] !Int !.[.[a]] /* enqLen enqList deqLen deqList */

adjust :: !u:(Queue .a) -> v:(Queue .a), [u <= v]
adjust q=:(Queue enqLen enqList deqLen deqList)
 | enqLen > 3 && enqLen >= deqLen = Queue 0 [] (enqLen + deqLen) (deqList ++ [reverse enqList])
 | otherwise = q

enq :: .a !u:(Queue .a) -> v:(Queue .a), [u <= v]
enq a (Queue enqLen enqList deqLen deqList)
 = adjust (Queue (enqLen + 1) [a:enqList] deqLen deqList)

deq :: !u:(Queue .a) -> (.a, !v:(Queue .a)), [u <= v]

deq (Queue enqLen enqList deqLen [[]:deqList])
 = deq (Queue enqLen enqList deqLen deqList)

deq (Queue enqLen enqList deqLen [[a:as]:deqList])
 = (a, adjust (Queue enqLen enqList (deqLen - 1) [as:deqList]))

deq (Queue enqLen enqList 0 deqList)
 = deq (Queue 0 [] enqLen [reverse enqList])

newq :: .(Queue .a)
newq = Queue 0 [] 0 []

emptyq :: !.(Queue .a) -> .Bool
emptyq (Queue 0 _ 0 _) = True
emptyq _ = False

Introductory Course In Math: No Background Needed

1. Notion of representation
2. Notion of encoding
3. Requirements to glyphs: equality, recognisability, one might always realise where one ends and another begins
4. Deductive apparatus, mathematical theories
5. Interpretations of mathematical theories, constants
6. Variables, historic excursion into prop calc, difference between variables and constants; quantors; variable substitution and its pitfalls
7. What is Existence
8. What is Truth
9. Art of proof
10. Soundness, completeness, consistency
11. Proof theory
12. Model theory

(12 lessons, first two or three are short and may be conducted together)

Monadic Arithmetics

/* Stop >>= \a -> >>= \b insane! */

instance + (m a) | + a & Monad m
where
 (+) ma mb = ma >>= \a -> mb >>= \b -> return $! a + b

instance - (m a) | - a & Monad m
where
 (-) ma mb = ma >>= \a -> mb >>= \b -> return $! a - b

instance * (m a) | * a & Monad m
where
 (*) ma mb = ma >>= \a -> mb >>= \b -> return $! a * b

instance / (m a) | / a & Monad m
where
 (/) ma mb = ma >>= \a -> mb >>= \b -> return $! a / b

instance mod (m a) | mod a & Monad m
where
 (mod) ma mb = ma >>= \a -> mb >>= \b -> return $! a mod b

instance rem (m a) | rem a & Monad m
where
 (rem) ma mb = ma >>= \a -> mb >>= \b -> return $! a rem b

/* http://hpaste.org/10673 */

Heterogeneous lists for poor Concurrent Clean programmer

module sh /* search hlist */

import Same, FuncPipe, UnitType, UndefValue, Float, ErrorValue, Char, Logical, String
import Map, FPToolbox

Start = test2

//////////////////////////////

:: O = O
:: I a = I a

pos0 = O
add1 a = I a
add2 a = I (I a)
add3 a = I (I (I a))
pos1 = add1 pos0
pos2 = add2 pos0
pos3 = add3 pos0
pos4 = add1 pos3
pos5 = add2 pos4
pos6 = add3 pos3
pos7 = add3 pos4
pos8 = add3 pos5

///////////////////////////////////////////////////////

test2 :: String
test2 = selectHList pos0 ("hello",(-15.84,(100,(True,<>))))

class SelectHList i a t
where
 selectHList :: i a -> t

instance SelectHList (I i) (a,b) t | SelectHList i b t
where
 selectHList (I i) (a,b) = selectHList i b

instance SelectHList O (a,b) a` | Same a a`
where
 selectHList O (a,b) = same a

////////////////////////////////////////////////////

test :: String
test = searchHList ("hello",(-15.84,(100,(True,<>))))

class SearchHList t a
where
 searchHList :: !a -> t

instance SearchHList t <>
where
 searchHList <> = error "SearchHList: type not found!"

instance SearchHList t (a,b) | IfTypeEqual t a & SearchHList t b // allways inline this instance
where
 searchHList (a,b) = ifTypeEqual a $ searchHList b

class IfTypeEqual t a
where
 ifTypeEqual :: a t -> t

instance IfTypeEqual Int Int  where ifTypeEqual a b = a
instance IfTypeEqual Bool Bool  where ifTypeEqual a b = a
instance IfTypeEqual Float Float where ifTypeEqual a b = a
instance IfTypeEqual Char Char  where ifTypeEqual a b = a
instance IfTypeEqual String String where ifTypeEqual a b = a
instance IfTypeEqual [t] [a] | IfTypeEqual t a
where
 ifTypeEqual a b = map (\(ae,be) -> ifTypeEqual ae be) $ zip2 a b

instance IfTypeEqual t a where ifTypeEqual a f = f

My Desktop 2008

Laziness without laziness

foldM_ f xs = fold (\a e -> a >> f e) (return ()) xs

Instead of making chain of dynamically created functions from data list it is better to create a function that makes next function in chain

foldM_ f l = foldLoop l
where
        foldLoop []     = return ()
 foldLoop [x:xs] = f x >> foldLoop xs

Notice that this fragment does not use any language laziness.