**Paste:**#108295**Author(s):**geophf and 1HaskellADay**Language:**Haskell**Channel:**-**Created:**2014-07-28 17:07:48 UTC**Revisions:**

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 | module Control.Boolean where import Prelude hiding (and, or, not) infixr 2 -| {-- A solution to the Boolean logic exercise at http://lpaste.net/108272 Okay, so I guess we are doing this thing. From the P-99 Prolog problem set we are looking at P46 through P48: define truth tables for and, or, nand, nor, xor, impl, equ, and not. There's a twist to this problem, however: You only have one, count'm: one, operator in the base language from which you define all the other operators, so choose wisely. We choose the nand-approach for this solution set. The nor-approach also provides complete coverage of boolean logic. --} and, or, nand, nor, xor, impl, equ :: Bool -> Bool -> Bool nand True True = False nand _ _ = True -- tt: t t = f, t f = t, f t = t, f f = t and a b = not (nand a b) -- tt: t t = t, t f = f, f t = f, f f = f or a b = nand (not a) (not b) -- tt: t t = t, t f = t, f t = t, f f = f nor a b = not (or a b) -- tt: t t = f, t f = f, f t = f, f f = t xor a b = not (equ a b) -- tt: t t = f, t f = t, f t = t, f f = f impl a b = nand a (not b) -- tt: t t = t, t f = f, f t = t, f f = t (-|) :: Bool -> Bool -> Bool a -| b = impl a b equ a b = or (and a b) (nor a b) -- tt: t t = t, t f = f, f t = f, f f = t not :: Bool -> Bool not = nand True -- tt: t = f, f = t {-- AND THEN, once you've defined your operators, define a function, table, that returns a table of truth values for an input expression: --} table :: [(Bool, Bool)] -> (Bool -> Bool -> Bool) -> [Bool] table truths fn = map (uncurry fn) truths -- please note I changed the signature of table so that it would -- unwrap the arguments directly with uncurry. testBool :: (Bool -> Bool -> Bool) -> [Bool] testBool = table [(a, b) | a <- [True, False], b <- [True, False]] {-- So, you get this: *Control.Boolean> testBool and [True,False,False,False] *Control.Boolean> testBool nor [False,False,False,True] *Control.Boolean> testBool xor [True,False,False,True] *Control.Boolean> testBool equ [False,True,True,False] *Control.Boolean> testBool impl [True,False,True,True] A little bit of history from wikipedia: Boole's work and that of later logicians initially appeared to have no engineering uses. Claude Shannon attended a philosophy class at the University of Michigan which introduced him to Boole's studies. Shannon recognised that Boole's work could form the basis of mechanisms and processes in the real world and that it was therefore highly relevant. In 1937 Shannon went on to write a master's thesis, at the Massachusetts Institute of Technology, in which he showed how Boolean algebra could optimise the design of systems of electromechanical relays then used in telephone routing switches. He also proved that circuits with relays could solve Boolean algebra problems. Employing the properties of electrical switches to process logic is the basic concept that underlies all modern electronic digital computers. Victor Shestakov at Moscow State University (1907–1987) proposed a theory of electric switches based on Boolean logic even earlier than Claude Shannon in 1935 on the testimony of Soviet logicians and mathematicians Yanovskaya, Gaaze-Rapoport, Dobrushin, Lupanov, Medvedev and Uspensky, though they presented their academic theses in the same year, 1938.[clarification needed] But the first publication of Shestakov's result took place only in 1941 (in Russian). Hence Boolean algebra became the foundation of practical digital circuit design; and Boole, via Shannon and Shestakov, provided the theoretical grounding for the Digital Age.[34] https://en.wikipedia.org/wiki/George_Boole --} |