experimenting with FLENG

• https://cdn.kinopio.club/szw5ARj8OnQ-EQfMwP6Bt/cole-freeman.800x.dither.png
• https://cdn.kinopio.club/zMhrZo-ZoE5aGDtN-ezBp/clipboard-20241126-220929.webp
• https://kinopio.club/mQkFBquD90gi3re33v9mU/-TIKeqVHkrr-zecXxDOmn
• https://kinopio.club/mQkFBquD90gi3re33v9mU/O1D8g--eHs9qtpfftC9kO
• https://kinopio.club/mQkFBquD90gi3re33v9mU/DSjC0GEmEDP5KRAN6pR93
• https://kinopio.club/mQkFBquD90gi3re33v9mU/qD4pgbJUEi8N7HvWtk1sK
• https://www.ueda.info.waseda.ac.jp/~ueda/pub/GHCthesis.pdf "Guarded Horn Clauses" — PhD Thesis, Kazunori Ueda
• https://www.ueda.info.waseda.ac.jp/~ueda/pub/tr103new2.pdf Kazunori Ueda — Guarded Horn Clauses
• ## bounded buffers
• now let's wrap `transformer`, and have it block until the consumer sends a "ready" signal ``` -initialization(main). router(ready(_), Lines, Msgs, Next) :- transformer(Lines, Msgs, Next). transformer([], Out, _) :- Out = []. transformer([X|Xs], Out, Buf) :- Buf = [_|Next], Out = [message(X, Response)|Rest], router(Response, Xs, Rest, Next). consumer(_, []). consumer(I, [message(X,_)|Xs]) :- fmt:format("consumer: ~q\n", [X]), J is I + 1, consumer(J, Xs). main :- Buf = [_|Next], io:read_lines_bounded(stdin, Buf, Lines), transformer(Lines, Msgs, Next), consumer(0, Msgs). ```
• implement the message passing, with some forced sequential processing and delays for the sake of illustration ``` -initialization(main). timestamped(Msg, Args) :- timer:get_time_of_day(time(D,S,M)), list:append(["[~q:~q:~q] ", Msg], Fmt), fmt:format(Fmt, [D,S,M|Args]). router(ready(Id), Lines, Msgs, Next) :- timestamped("router: got ready signal from consumer ~d\n", [Id]) & transformer(Lines, Msgs, Next). transformer([], Out, _) :- Out = []. transformer([X|Xs], Out, Buf) :- Buf = [_|Next], Out = [message(X, Response)|Rest], router(Response, Xs, Rest, Next). consumer(_, []). consumer(I, [message(X,Response)|Xs]) :- timestamped("consumer ~d: ~q\n", [I, X]), timer(500, Done, _), when(Done, Response = ready(I)), J is I + 1, consumer(J, Xs). main :- Buf = [_|Next], io:read_lines_bounded(stdin, Buf, Lines), transformer(Lines, Msgs, Next), consumer(0, Msgs). ```
• ``` $ N=5; fleng incomplete-messages.ghc -o incomplete-messages && ./incomplete-messages < <(for ((i=0;i<N;i++)); do head -c 16 /dev/urandom | base64; done) [20152:23132:746689] consumer 0: "rt14GLdzzdaO83JmUGLxPA==" [20152:23133:246795] router: got ready signal from consumer 0 [20152:23133:247047] consumer 1: "I49w6mkIWjsrLP9DfbTtLw==" [20152:23133:747161] router: got ready signal from consumer 1 [20152:23133:747421] consumer 2: "Qn4sUDlv8IUc8nuVeEpinQ==" [20152:23134:247621] router: got ready signal from consumer 2 [20152:23134:247874] consumer 3: "3pfwazVw6w3Yad9j8KOOzQ==" [20152:23134:747960] router: got ready signal from consumer 3 [20152:23134:748189] consumer 4: "+rNJE5UkTydOHMWP02gv9Q==" [20152:23135:248386] router: got ready signal from consumer 4 ```
• ## difference lists
• assemble multiple distinct lists into on
• the key here is that the tail of each distinct sub-list is unified with either the terminal empty list or one of the other sublists
• each forked process receives a variable representing the tail
• so you can process the sub-lists in parallel, and assemble them in constant time
• intersect.ghc — this example's straight from the strand book ``` -initialization(main). intersect(L, M, Out) :- intersect1(L, M, [Out|[]]). intersect1([X|Xs], M, Out, End) :- member_add(X, M, Out, Acc), intersect1(Xs, M, Acc, End). intersect1([], _, Out, End) :- Out = End. member_add(X, [X|_], Out, End) :- Out = [X|End]. member_add(X, [Y|Ys], Out, End) :- X =\= Y | member_add(X, Ys, Out, End). member_add(_, [], Out, End) :- Out = End. main :- intersect([a,b,c,d], [c,e,f,d], Intersection), fmt:format("~q\n", [Intersection]). ```
• ## short-circuits
• https://cdn.kinopio.club/PAxF_7QOJFEdFrSHfW1nR/image.png