hofs.erl

-module(hofs).
-export[double_All/1,evens/1,prod/1,zip/2,zip_with/3,zip_with_hof/3,zip_hof/2].

double(X)->
    2*X.
double_All(Lst) -> 
    lists:map(fun double/1, Lst).

even(X) ->
    X rem 2 == 0.
evens(Lst) ->
    lists:filter(fun even/1, Lst).

prod(X,Y) ->
    X*Y.
prod(Lst)->
    lists:foldr(fun prod/2,1,Lst).
zip(Xs,Ys)->
    zip(Xs,Ys,[]).
zip([],_,Acc) ->
    Acc;
zip(_,[],Acc) ->
    Acc;
zip([X|Xs],[Y|Ys],Acc) ->
    [{X,Y}|zip(Xs,Ys,Acc)].
zip_with(F,Xs,Ys)->
    zip_with(F,Xs,Ys,[]).
zip_with(_F,[],_,Acc)->
    Acc;
zip_with(_F,_,[],Acc) ->
    Acc;
zip_with(F,[X|Xs],[Y|Ys],Acc) ->
    [F(X,Y)|zip_with(F,Xs,Ys,Acc)].

zip_with_hof(F,Xs,Ys)->
    lists:map(fun({X,Y})->F(X,Y) end ,zip(Xs,Ys)).
zip_hof(Xs,Ys) ->
    zip_with_hof(fun(X,Y)-> {X,Y} end , Xs,Ys).