# HG changeset patch
# User IBBoard <dev@ibboard.co.uk>
# Date 1506368992 -3600
# Node ID 178b18b4f9ba16db311eb031c32bd93041e4cb8f
# Parent  b94161b72db671a08cd61bf5320955dd459bb639
Start experimenting with Prolog

diff -r b94161b72db6 -r 178b18b4f9ba 3-Prolog/day1-food.pl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/3-Prolog/day1-food.pl	Mon Sep 25 20:49:52 2017 +0100
@@ -0,0 +1,19 @@
+% Define some foods and "flavours".
+% Note that this is Americanised, so some of these definitions are generous!
+food_type(velveeta, cheese).
+food_type(ritz, cracker).
+food_type(spam, meat).
+food_type(sausage, meat).
+food_type(jolt, soda).
+food_type(twinkie, dessert).
+
+flavour(sweet, dessert).
+flavour(savoury, meat).
+flavour(savoury, cheese).
+flavour(sweet, soda).
+
+food_flavour(X, Y) :- food_type(X, Z), flavour(Y, Z).
+% Note: flavour(sweet, What) will return 'yes' and a closed set of answers because it is just all of the facts
+% but "food_flavour(What, meat)" will return answers and then say 'no', because it hasn't been given a flavour()
+% fact for "ritz"/"cracker".
+% This doesn't explain why "food(What, meat)" returns "no" after spam and sausage, though.
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diff -r b94161b72db6 -r 178b18b4f9ba 3-Prolog/day1-wallaceandgrommit.pl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/3-Prolog/day1-wallaceandgrommit.pl	Mon Sep 25 20:49:52 2017 +0100
@@ -0,0 +1,16 @@
+% Start with some simple facts
+% Note: like semantic systems, names are intrinsicly equal variables
+% (or variables don't exist). Names are called "atoms"
+likes(wallace, cheese).
+likes(grommit, cheese).
+likes(wendolene, sheep).
+% Each statement ends with a fullstop
+
+% Rule syntax is a bit odd (":-" and "\+") but we're saying that X and Y
+% can be friends if X and Y like the same thing.
+% Poor Wendolene.
+friend(X, Y) :- \+(X = Y), likes(X, Z), likes(Y, Z).
+% "\+" is apparently logical negation (because of course it is)
+% so the first "subgoal" stops Wallace being Wallace's friend
+%
+% Note: Prolog nomenclature is that this is "friend/2" - friend func with 2 params
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diff -r b94161b72db6 -r 178b18b4f9ba 3-Prolog/readme.txt
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/3-Prolog/readme.txt	Mon Sep 25 20:49:52 2017 +0100
@@ -0,0 +1,14 @@
+Installed gprolog from https://software.opensuse.org/package/gprolog
+
+Some documentation says that Prolog may accept a shebang as the first line, but gprolog didn't like it.
+
+Some editors will assume ".pl" means Perl. You may need to change your syntax highlighting.
+
+Running code involves calling "gprolog" without parameters and then running "['filename']." (fullstop terminates the commend).
+You can then query it with function calls (e.g. "likes(grommit, sheep)." in the Wallace & Grommit example). Prolog always
+returns "yes" or "no" at a prompt when it has finished.
+
+When you ask a question with a placeholder, the placeholder has to be capitalised. Lower-case makes it an atom.
+When Prolog returns its answers, type ";" to get the next response. Sometimes Prolog will end multiple responses
+with "no", sometimes with "yes". This depends on whether it needs to do more calculations to check for more answers ("no")
+or whether it knows it successfully gave you everything ("yes").
\ No newline at end of file