Parsing with prolog

Question

I am trying to parse with prolog:

I need to run a code which recieves a text in the command and parse it depending of the input.

Command cal returns calendar(Month, Year) where month ∈ [1-12] and year ∈ [1-9999]. If there is no month given, it returns the year, if both are not specified return current month and year. Example.

Option1

?- read_sentence(X). |: cal 1 2000 X = calendar(1,2000).

Option2

?- read_sentence(X). |: cal 2000 X = calendar(2000).`

Option3

?- read_sentence(X). |: cal X = calendar(1,2016).

So far I am able to read the sentence, and print it, but I have no idea how to parse or even where to begin.

read_sentence(X) :- get0(C), read_sentence(X, L,C), name(X, L). read_sentence(_, [], X) :- member(X, `.\n\t`), !. read_sentence(X, [C|L], C) :- get0(C1), read_sentence(X, L, C1).

Which does:

?- read_sentence(X). |: Hello there X = 'Hello there'.

Can you explain what you mean by parse? The thing to be parsed appears to be what you get from read_sentence; what should be the result of parsing? — Scott Hunter
– Scott Hunter, Commented Jan 5, 2016 at 20:11
I mean if I enter read_sentence(X). This will open a command line where an input is required. Input: cal 1 200 The code has to recognize that it has "cal" "number between 1-12" and "number between 1 and 9999" Output: calendar(1,200) — Saul Garcia
– Saul Garcia, Commented Jan 5, 2016 at 20:17
Which means you need a way to break down the input string into a list of individual words, correct? — Scott Hunter
– Scott Hunter, Commented Jan 5, 2016 at 21:06

Scott Hunter · Accepted Answer · 2016-01-05 21:43:31Z

SWI-Prolog has a predicate, split_string, for splitting up strings into "words", which might be what you need for this rather simple parsing, which you could then use to decide how to invoke calendar.

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