GeoffChurch’s gists

GeoffChurch / subgroup_lattice.sage

Last active January 19, 2022 16:30

Plot subgroup lattice with short labels and normal subgroups highlighted. Works with Sage 9.2, Python 3.9.5

	def relabel(xs, f):
	clazz = type(xs[0])
	new_clazz = type(f"{clazz}_relabeled", (clazz,), {"__str__" : f})
	for x in xs:
	x.__class__ = new_clazz

	def norms_abnorms(subgroups, G):
	norms = []
	abnorms = []
	for s in subgroups:

GeoffChurch / mi_dcg.pl

Last active February 25, 2022 19:47

DCG-ification of mi_list3 from Power of Prolog chapter on meta-interpreters

	mi_dcg_clause, [] --> [natnum(0)].
	mi_dcg_clause, [natnum(X)] --> [natnum(s(X))].
	mi_dcg_clause, [always_infinite] --> [always_infinite].

	mi_dcg --> [].
	mi_dcg --> mi_dcg_clause, mi_dcg.

	%% Original version from https://www.metalevel.at/acomip/ :

	mi_ldclause(natnum(0), Rest, Rest).

GeoffChurch / npda_palindrome.pl

Created March 6, 2022 03:37

Nondeterministic pushdown automaton interpreter adapted from Art of Prolog 2e, Ch 17

GeoffChurch / double_negation_elimination.hs

Last active March 22, 2022 20:24

Double negation elimination in Haskell assuming universe of only 2 types: () and Void

GeoffChurch / reif_dcg.pl

Last active March 23, 2022 14:49

Reified DCG utils

	:- use_module(library(reif)).

	phrase_t(P, I, O, T) :- phrase(call(P, T), I, O).

	if_(If, Then, Else, I, O) :-
	if_(phrase_t(If, I, M),
	phrase(Then, M, O),
	phrase(Else, M, O)).

	% Example:

GeoffChurch / copy_term_4.pl

Last active October 17, 2022 22:00

	copy_term(VarsIn, In, VarsOut, Out) :-
	term_variables(In, AllVarsIn),
	maplist(list_to_ord_set, [AllVarsIn, VarsIn], [AllVarsInOrdSet, VarsInOrdSet]),
	ord_subtract(AllVarsInOrdSet, VarsInOrdSet, PreservedVars),
	copy_term(PreservedVars-VarsIn-In, PreservedVars-VarsOut-Out).

GeoffChurch / unifier.pl

Created June 16, 2022 21:11

Like SWI Prolog's unifiable/3, but maintains the left-right order of the terms in the unifier, rather than placing variables on the left.

	%! unifier(@Term1, @Term2, ?Unifier) is semidet.
	%
	% Like SWI Prolog's unifiable/3, but maintains the left-right order of the terms in the unifier, rather than placing variables on the left.
	unifier(A, B, Unifier) :-
	rb_empty(Seen),
	unifier_(Seen, A, B, [], Unifier0),
	exclude(unifier_is_reflexive, Unifier0, Unifier1),
	sort(Unifier1, Unifier).

	unifier_(Seen0, A, B, Unifier0, Unifier) :-

GeoffChurch / foldargs.pl

Created October 17, 2022 16:38

	foldargs(Goal, A, B) -->
	{ maplist(functor_arity_term_args(_, _), [A, B], [As, Bs]) },
	foldl(Goal, As, Bs).

	functor_arity_term_args(Functor, Arity, Term, Args) :-
	functor(Term, Functor, Arity),
	Term =.. [_\|Args].

GeoffChurch / cata.pl

Last active May 16, 2023 18:22

Declarative catamorphism with meta-language escapes which can be used e.g. to solve for variable bindings in the codomain.

	unescape(\X, X). % Subterms, and in particular logic variables, can be marked as pre-evaluated.

	cata(Alg) --> unescape *-> {} ; mapargs(cata(Alg)), call(Alg).

	% Example:

	alg( 0 + 0, 0).
	alg( 0 + 1, 1).
	alg( 1 + 0, 1).
	alg( 1 + 12, 13).

GeoffChurch / rule30_animation.py

Last active May 14, 2023 23:03

Wolfram's "rule 30" cellular automaton. Read it, download it, and then execute `python rule30_animation.py` from your terminal in the same directory.

	from os import get_terminal_size
	from time import sleep

	terminal_size = get_terminal_size()
	num_cells = terminal_size.columns # We'll have as many cells as can fit in the terminal's width
	sleep_time = 4.0 / terminal_size.lines # Animation speed will be proportional to the terminal's height

	# Lookup table for Wolfram's "rule 30" cellular automaton
	RULE_30 = {
	(0,0,0) : 0,

Geoffrey Churchill GeoffChurch