-module(funparse).
-compile(export_all).
-import(lists, [reverse/1]).
%17
%% > hof:parse([a,c]).
%% {ok,{'and',{'or',1,{const,a}},{'or',1,{const,c}}}}
%% > hof:parse([a,d]).
%% {ok,{'and',{'or',1,{const,a}},{'or',2,{const,d}}}}
%% > hof:parse([b,c]).
%% {ok,{'and',{'or',2,{const,b}},{'or',1,{const,c}}}}
%% > hof:parse([b,d]).
%% {ok,{'and',{'or',2,{const,b}},{'or',2,{const,d}}}}
%% > hof:parse([a,b]).
%% fail
%17
%% Grammar = (a | b) & (c | d)
%12
parse(List) ->
(grammar())(List).
%12
%13
grammar() ->
pand(
por(pconst(a), pconst(b)),
por(pconst(c), pconst(d))).
%13
%14
pconst(X) ->
fun (T) ->
case T of
[X|T1] -> {ok, {const, X}, T1};
_ -> fail
end
end.
%14
%15
por(P1, P2) ->
fun (T) ->
case P1(T) of
{ok, R, T1} ->
{ok, {'or',1,R}, T1};
fail ->
case P2(T) of
{ok, R1, T1} ->
{ok, {'or',2,R1}, T1};
fail ->
fail
end
end
end.
%15
%16
pand(P1, P2) ->
fun (T) ->
case P1(T) of
{ok, R1, T1} ->
case P2(T1) of
{ok, R2, T2} ->
{ok, {'and', R1, R2}};
fail ->
fail
end;
fail ->
fail
end
end.
%16
