From e237e9e019e1c8610513c655f7df091015cf1a90 Mon Sep 17 00:00:00 2001
From: Sergiu Ivanov <sivanov@colimite.fr>
Date: Wed, 3 Jun 2020 22:51:06 +0200
Subject: [PATCH] functions: Add tbf.

---
 functions.rkt | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/functions.rkt b/functions.rkt
index 45d155b..b45b02e 100644
--- a/functions.rkt
+++ b/functions.rkt
@@ -10,6 +10,9 @@
 (require "utils.rkt")
 
 (provide
+ ;; Structures
+ (contract-out
+  [struct tbf ((weights number?) (threshold (vectorof number?)))])
  ;; Functions
  (contract-out
   [tabulate (-> procedure? (listof generic-set?) (listof list?))]
@@ -23,7 +26,9 @@
   [enumerate-boolean-functions/list (-> number? (stream/c procedure?))]
   [random-boolean-table (-> number? (listof (*list/c boolean? boolean?)))]
   [random-boolean-function (-> number? procedure?)]
-  [random-boolean-function/list (-> number? procedure?)]))
+  [random-boolean-function/list (-> number? procedure?)]
+  [tbf-w (-> tbf? (vectorof number?))]
+  [tbf-θ (-> tbf? number?)]))
 
 (module+ test
   (require rackunit))
@@ -197,3 +202,16 @@
     (define f (random-boolean-function/list 2))
     (check-false (f '(#f #f))) (check-true (f '(#f #t)))
     (check-true (f '(#t #f))) (check-false (f '(#t #t)))))
+
+
+;;; ===========================
+;;; Threshold Boolean functions
+;;; ===========================
+
+;;; A threshold Boolean function (TBF) is a pair (w, θ), where w is a
+;;; vector of weights and θ is the threshold.
+(struct tbf (weights threshold) #:transparent)
+
+;;; Unicode shortcuts for accessing the elements of a TBF.
+(define tbf-w tbf-weights)
+(define tbf-θ tbf-threshold)