Racket Haskell ; Function definition and application -- Function definition and application (lambda(xy)(*xy)) \x y ->x*y (+345) ; 12 (==)3(4- 25) -- False ((lambda(x)(+3x)) 10) ; 13 (\x ->x+3) 10 -- 13 ; Name bindings -- Name bindings (definex 10) x= 10 (define(fz)(first(restz))) fz=z+ 10 (let*([y(+ 10 20)] lety= 10+ 20 [z(+ 10y)]) z= 10+y (*yz)) iny*z ; Syntactic forms -- If (note that && and || are just functions) (and #f(/10)) ; #f fx= (or #t(/10)) ; #t ifx == 10 (if #t then 16 42 else-20 (/10)) ; 42 (cond[#f(/10)] [#t 42] [(/10) 25] [else1]) ; 42 ; Pattern matching -- Pattern matching (define/match(commentx) comment7="Lucky" [(7) "Lucky"] comment 13="Unlucky" [(13) "Unlucky"] comment_="Other" [(_) "Other"]) (define/match(f lst) f[]= 100 [((list)) 100] f (x:xs)=x+ length xs [((consx xs)) (+x(length xs))]) ; Lists -- Lists (cons2(cons3 null)) ; '(2 3) 2:3:[] -- [2,3] (list12 20) ; '(1 2 20) [1,2,20] -- [1,2,20] (first(list123)) ; 1 head[1,2,3] -- 1 (rest(list123)) ; '(2 3) tail[1,2,3] -- [2,3] (null? null) ; #t null[] -- True (length(list1 205)) ; 3 length[1,2,20] -- 3 (append(list12)(list46) ; '(1 2 4 6) [1,2] ++[4,6] -- [1,2,4,6] (member2(list123)) ; '(2 3) elem2[1,2,3] -- True (member4(list123)) ; #f elem4[1,2,3] -- False (list-ref(list2 401)1) ; 40 [20,40,1]!!1 -- 40 (map(lambda(x)(*3x)) map(\x ->3* x) [1,2,3] -- [3,6,9] (list123)) ; '(3 6 9) (filter(lambda(x)(<3x)) filter(\x ->3< x) [10,-4,15] -- [10,15] (list 10 -4 15)) ; '(10 15) (foldl+ 15(list123)) ; (3 + (2 + (1 + 15))) foldl(+) 15[1,2,3] -- (((15 + 1) + 2) + 3) (apply-(list 163)) ; 13 f$x=fx -- unary function application ; Maps -- Maps (hash) ; fg Map.empty -- fg (hash "a"1 "b"2) ; fa: 1, b: 2g Map.fromMap [("a",1), ("b",2)] -- fa: 1, b: 2g (hash-has-key? hash key) ; returns boolean Map.member key map -- returns Bool (hash-set hash key value) ; returns new map Map.insert key value map -- returns new map (hash-ref hash key) ; map lookup map! key -- map lookup Streams, Continuations, and Choice Haskell types ; Streams -- Type annotations empty-stream ; empty stream True:: Bool (define-syntax stream-cons (&&):: Bool -> Bool -> Bool (syntax-rules() head:: [a] ->a [(stream-cons <first> <rest>) (==):: Eqa =>a ->a -> Bool (cons(thunk <first>)(thunk <rest>))])) 1:: Numa =>a -- multiple type class constraints (define(stream-first stream) ((car stream))) myFunc::(Eq a, Num b) =>a ->b -> Bool (define(stream-rest stream) ((cdr stream))) ; Choice implementation -- Type declarations, type synonyms (define choices null) ; a stack of choices data Point= Point Integer Integer (define DONE 'done) data BTreea= Empty| BTreea(BTree a) (BTree a) type String=[Char] (define-syntax -< (syntax-rules() -- Type class instantiation [(-< <expr1>) <expr1>] instance Show Point where [(-< <expr1> <expr2>...) show (Point x y)= (shiftk "(" ++ (show x) ++"," ++ (show y) ++")" (add-choice!(thunk(k(-< <expr2>...)))) (k <expr1>))])) -- Functors and monads class Functorf where (define(next!) fmap:: (a -> b) ->fa ->fb (if(null? choices) (shiftk DONE) class Monadm where (reset((get-choice!))))) (>>=)::ma -> (a -> m b) ->mb return::a ->ma (define(backtrack!)(shiftk(next!))) -- Modeling failing computations data Maybea= Nothing| Justa -- data Eitherab= Lefta| Rightb -- Modeling mutation data Statesa= State (s -> (a, s)) state:: (s -> (a, s)) -> Statesa runState:: Statesa ->s -> (a, s) runState(State f) init= f init get:: Statess get= State(\state -> (state, state)) put::s -> States() putx= State(\_ ->((), x)) -- Standard input/output actions getLine::IO String -- read line from stdin, -- not including newline putStrLn:: String ->IO() -- print string to stdout, -- with terminating newline -- NOTE: Maybe, (Either a), (State s), [], and IO -- are all instances of Functor and Monad..