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
|
module Interpreter where
import Data.Function
import qualified Data.Map as M
{- VAM 2P, done the lazy way -}
data StrTable =
StrTable Int (M.Map Int String)
data Instr
= Atom Int -- unify a constant
| Struct (Int, Int) -- unify a structure with arity
| NoGoal -- trivial goal
| Goal -- we start a new goal, set up backtracking etc
| Call -- all seems okay, call the goal
| LastCall -- tail call the goal
deriving Show
type Defs = M.Map (Int, Int) [Instr]
data Interp =
Interp
{ defs :: Defs
, hed :: [Instr]
, gol :: [Instr]
, stk :: [[Instr]]
}
prove :: [Instr] -> Defs -> Bool
prove g ds =
let i0 = Interp ds [NoGoal] [LastCall] [g]
run (Left x) = x
run (Right x) = run $ pr Right Left x
in run (Right i0)
pr :: (Interp -> a) -> (Bool -> a) -> Interp -> a
pr c f i = go i
where
go i@Interp {hed = (Atom a:hs), gol = (Atom b:gs)} -- unify constants
| a == b = c i {hed = hs, gol = gs}
go i@Interp {hed = (Struct a:hs), gol = (Struct b:gs)} -- unify structs
| a == b = c i {hed = hs, gol = gs}
go i@Interp {hed = [NoGoal], gol = [LastCall], stk = []} = f True -- final success
go i@Interp { hed = [NoGoal]
, gol = [LastCall]
, stk = ((Goal:Struct f:gs):ss)
} -- goal succeeded
| Just nhs <- defs i M.!? f = c i {hed = nhs, gol = gs, stk = ss}
go i@Interp {hed = [NoGoal], gol = (Call:Goal:Struct f:gs)} -- next goal
| Just nhs <- defs i M.!? f = c i {hed = nhs, gol = gs}
go i@Interp {hed = (Goal:Struct f:hs), gol = [LastCall]} -- tail call
| Just nhs <- defs i M.!? f = c i {hed = nhs, gol = hs}
go i@Interp {hed = (Goal:Struct f:hs), gol = (Call:gs), stk = ss} -- normal call
| Just nhs <- defs i M.!? f = c i {hed = nhs, gol = hs, stk = gs : ss}
go _ = f False -- bad luck
|
