~ashton314/microKanren

39699c107efeb033daea56746cf4c21ec8a6a1d4 — Ashton Wiersdorf 5 months ago 412c118
add codeblocks
1 files changed, 23 insertions(+), 19 deletions(-)

M index.md
M index.md => index.md +23 -19
@@ 48,28 48,32 @@ It *can* return another variable; if the last thing that one variable points to 

The [unify](kanren.rkt) function take two *things*, `u` and `v`, and tries to make them line up according to the substitution that you give as well.

    (unify '(1 2 3) '(2 3 4) '())
    #f
    
    (unify '(1 2 3) '(1 2 3) '())
    '()
    
    (unify '(1 2 3) '(1 2 3) '(yay))
    '(yay)
    
    (unify (list 1 2 3) (list 1 (var 0) 3) '())
    (list (cons (var 0) 2))
    
    (unify (list 1 2 3) (list 1 (var 0) 3) `((,(var 0) 4)))
    #f
```racket
(unify '(1 2 3) '(2 3 4) '())
#f

(unify '(1 2 3) '(1 2 3) '())
'()

(unify '(1 2 3) '(1 2 3) '(yay))
'(yay)

(unify (list 1 2 3) (list 1 (var 0) 3) '())
(list (cons (var 0) 2))

(unify (list 1 2 3) (list 1 (var 0) 3) `((,(var 0) 4)))
#f
```

This example illustrates how the `walk` function drills down:

    (walk (var 0) `((,(var 0) . ,(var 1)) (,(var 1) . ,(var 2))))
    (var 2)
    
    (unify (list 1 2 3) (list 1 (var 0) 3) `((,(var 0) . ,(var 1)) (,(var 1) . 2)))
    (list (cons (var 0) (var 1)) (cons (var 1) 2))
```racket
(walk (var 0) `((,(var 0) . ,(var 1)) (,(var 1) . ,(var 2))))
(var 2)

(unify (list 1 2 3) (list 1 (var 0) 3) `((,(var 0) . ,(var 1)) (,(var 1) . 2)))
(list (cons (var 0) (var 1)) (cons (var 1) 2))
```

If we wanted to be able to unify more than just lists (e.g. rich structures) we would teach μKanren here in the `cond` how to walk those richer structures.