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duboissim 2024-03-14 15:32:14 +01:00
parent 59ea540c45
commit b100bf03d8
1 changed files with 102 additions and 1 deletions

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@ -1,3 +1,25 @@
:- use_module(library(dcg/basics)).
% DCG rule that checks if the remainder of the input
% starts with Delim (a list), but does not consume
% any input.
lookahead(Delim , L, L) :-
prefix(Delim , L).
% Checks if the remainder of the input starts with one
% of the items in the supplied list (as per lookahead /3).
lookaheads([H|T]) -->
lookahead(H), ! ; lookaheads(T).
% Reads text until one of the delimiters in Delims is
% encountered , then unifies R with the Prolog term parsed
% from the text.
% ! Will crash the parse if a delimiter is encountered
% but the intervening text is not a Prolog term (you
% dont have this handle this case).
prolog_term(R, Delims) -->
string(S), lookaheads(Delims), !, {
read_term_from_atom(S, R, []) }.
:- dynamic tables/0.
/*
Prints the names of all existing tables, one per line (use writeln/1).
@ -164,7 +186,86 @@ For example:
findall(Values, selec(persons,[+id,+first],[],Values), Projections)
returns: Projections = [[0, "Jeffrey"], [1, "Lorena"], [2, "Joseph"], ...
*/
/* selec(Table, Selectors, Conds, Projection). */
selec(Table, Selectors, Conds, Projection) :-
selec_help(Table, Selectors,[], [], ColumnNames, ColumnValue),
%remove combinations that don't exist
row(Table, Row),
has_value(ColumnValue, Row),
Projection = ColumnNames/ColumnValue.
%base case
selec_help(_, [], ColumnNames, ColumnValue, ColumnNames, ColumnValue).
/**
* Table: name of the table the selection is done one
* [Selector|Selectors] name(s) of the column(s) for selection
* AccCols: acumulator list for the column(s) name(s)
* AccVals: acumulator list for the row(s) values
* ColumnNames: List returning the column(s) name(s)
* ColumnValue: List returning the row values for each column
*/
selec_help(Table, [Selector|Selectors], AccCols, AccVals, ColumnNames, ColumnValue) :-
%check if table exist
(tabl(Table, Cols) ->
%check if column exist
member(Selector, Cols) ->
%find the value corresponding to the column in the row
nth0(Index, Cols, Selector),
row(Table, Row),
nth0(Index, Row, Value),
%go to next column tho evaluate
selec_help(Table, Selectors, [Selector|AccCols], [Value|AccVals], ColumnNames, ColumnValue)
;
string_concat(Selector, " isn't a column of table ", X),
string_concat(X, Table, Error),
throw(Error)
;
string_concat(Table, " doesn't exist.", Error), throw(Error)
).
/*
Check if a list has all the values in [Value|Rest]
*/
has_value([], _) :- !.
has_value([Value|Rest], List) :-
memberchk(Value, List),
has_value(Rest, List).
evaluate_condition_string(ConditionString) :-
atom_codes(AtomCondition, ConditionString), % Convert string to atom
read_term_from_codes(AtomCondition, Term, []), % Parse the term
call(Term). % Evaluate the parsed term
selec_column(Table, Column, Proj) :-
tabl(Table, Cols),
row(Table, Row),
nth0(I, Cols, Column),
nth0(I, Row, Value),
Proj = Value.
apply_cond(Table, Cond, Proj) :-
tabl(Table, Cols),
row(Table, Row),
nth0(I, Cols, Column),
nth0(I, Row, Value),
split_string(Cond, " ", "", SubStrings),
Decomp = SubStrings,
Decomp = [Column, Op, Value],
check_condition(Column, Op, Value),
Proj = Row.
check_condition(Left, =, Right) :-
Left =:= Right.
check_condition(Left, <, Right) :-
Left < Right.
check_condition(Left, >, Right) :-
Left > Right.
check_condition(Left, <=, Right) :-
Left =< Right.
check_condition(Left, >=, Right) :-
Left >= Right.
check_condition(Left, \=, Right) :-
Left =\= Right.
:- dynamic selec/3.
/*