Re: Detecting the presence of a pattern in an atom

Hi Steve:

You need not be afraid of DCGs. In Prolog, they are among your best friends.

For example:

% Here's the DCG

nothing("") --> "".

upper_alpha(A) --> [A], { code_type(A, upper) }.

lparen --> "(".

rparen --> ")".

upper_alpha_string([ A | B]) -->
    upper_alpha(A), (upper_alpha_string(B); nothing(B)).

parenthetic_phrase(A) -->
    lparen, upper_alpha_string(A), rparen.

% Here's how you use it in your application. 
% Convert string to codes before calling string_search/2.

string_search([], nil) :- 
    !, fail.

string_search(String, Atom) :-
    phrase(parenthetic_phrase(Codes), String, _), !,
    atom_codes(Atom, Codes).

string_search([_ | More], Atom) :-
    string_search(More, Atom).


 Tested:

?- string_search("acme ltd (HELLO) 123", X).
X = 'HELLO'.

Regards,
Jeff R.



 

 

-----Original Message-----
From: Carlo Capelli <[email protected]>
To: Steve Prior <[email protected]>
Cc: Prolog <[email protected]>
Sent: Tue, Oct 15, 2013 2:40 am
Subject: Re: [SWIPL] Detecting the presence of a pattern in an atom


2013/10/15 Steve Prior <[email protected]>

> This is not a homework problem.
>
> I've been writing code which retrieves a list of titles from a web page
> source and need to do a little pattern matching on each title.  A title
> might look like:
>
> Some name and some business name (ABC)
>
> I'm trying to get the "ABC".
>
> The titles don't have any formal grammar to them, but for starters I need
> to see if there is a substring which starts with '(' contains all upper
> case letters and ends with ')'.  I suppose it's possible that the title
> might contain multiple open/close parens, but I'd expect only one set to
> fit the all upper case criterion.
>
> It seems a bit much to do a DCG grammar for this and I know that a regex
> isn't the Prolog way of doing things, but don't remember what a better
> option would be.  I'm a bit rusty in Prolog, I picked it for this project
> because of SWI's html parsing abilities which I've already put to good use.
>
>
Michael regex pack, or XPCE regexes are available.

 ?- regex('\\(([A-Z]+)\\)', [], 'acme ltd (HELLO) 123', [P]), format('~s',
[P]).

HELLO

P = [72, 69, 76, 76, 79]

HTH Carlo



> Any pointers?
>
> Steve
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