factor/extra/rosetta-code/ternary-logic/ternary-logic.factor

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Factor

! Copyright (c) 2012 Anonymous
! See http://factorcode.org/license.txt for BSD license.
USING: combinators kernel ;
IN: rosetta-code.ternary-logic
! http://rosettacode.org/wiki/Ternary_logic
! In logic, a three-valued logic (also trivalent, ternary, or
! trinary logic, sometimes abbreviated 3VL) is any of several
! many-valued logic systems in which there are three truth values
! indicating true, false and some indeterminate third value. This
! is contrasted with the more commonly known bivalent logics (such
! as classical sentential or boolean logic) which provide only for
! true and false. Conceptual form and basic ideas were initially
! created by Ɓukasiewicz, Lewis and Sulski. These were then
! re-formulated by Grigore Moisil in an axiomatic algebraic form,
! and also extended to n-valued logics in 1945.
! Task:
! * Define a new type that emulates ternary logic by storing data trits.
! * Given all the binary logic operators of the original
! programming language, reimplement these operators for the new
! Ternary logic type trit.
! * Generate a sampling of results using trit variables.
! * Kudos for actually thinking up a test case algorithm where
! ternary logic is intrinsically useful, optimises the test case
! algorithm and is preferable to binary logic.
SINGLETON: m
UNION: trit t m POSTPONE: f ;
GENERIC: >trit ( object -- trit )
M: trit >trit ;
: tnot ( trit1 -- trit )
>trit { { t [ f ] } { m [ m ] } { f [ t ] } } case ;
: tand ( trit1 trit2 -- trit )
>trit {
{ t [ >trit ] }
{ m [ >trit { { t [ m ] } { m [ m ] } { f [ f ] } } case ] }
{ f [ drop f ] }
} case ;
: tor ( trit1 trit2 -- trit )
>trit {
{ t [ drop t ] }
{ m [ >trit { { t [ t ] } { m [ m ] } { f [ m ] } } case ] }
{ f [ >trit ] }
} case ;
: txor ( trit1 trit2 -- trit )
>trit {
{ t [ tnot ] }
{ m [ drop m ] }
{ f [ >trit ] }
} case ;
: t= ( trit1 trit2 -- trit )
>trit {
{ t [ >trit ] }
{ m [ drop m ] }
{ f [ tnot ] }
} case ;