python 示例分享---逻辑推理编程解决八皇后

可以和haskell ， prolog 一样做到模式匹配，

建立逻辑推到规则，描述问题，得出答案。

from pydatalog import pydatalog

pydatalog.create_atoms( 'n, n1, x, y, x0, x1, x2, x3, x4, x5, x6, x7' )
pydatalog.create_atoms( 'ok, queens, next_queen, pred, pred2' )

size = 8
ok( x1, n, x2 ) <= ( x1 != x2 ) & ( x1 != x2 + n ) & ( x1 != x2 - n )

pred( n, n1 )  <= ( n > 1 ) & ( n1 == n - 1 )
queens( 1, x ) <= ( x1._in( range( size ) ) ) & ( x1 == x[0] )
queens( n, x ) <= pred( n, n1 ) & queens( n1, x[:-1] ) & next_queen( n, x )

pred2( n, n1 )   <= ( n > 2 ) & ( n1 == n - 1 )
next_queen( 2, x ) <= ( x1._in( range( 8 ) ) ) & ok( x[0], 1, x1 ) & ( x1 == x[1] )
next_queen( n, x ) <= pred2( n, n1 ) & next_queen( n1, x[1:] ) & ok( x[0], n1, x[-1] ) 

print( queens( size, ( x0, x1, x2, x3, x4, x5, x6, x7 ) ) )