# probabilistic-prolog-F-ocaml.ml

```type term = Constant of int
| Compound of int*(term list)

let make_p = 0

let make_q = 1

let make_x = (Base 2.0)

let same (Variable variable1) (Variable variable2) =
variable1<=variable2 && variable2<=variable1

let rec binds p1 variable2 =
match p1 with
[] -> false
| ((variable1, _)::substitution) ->
if same variable1 variable2 then true else binds substitution variable2

let rec lookup_value variable1 ((variable2, value)::substitution) =
if same variable1 variable2
then value
else lookup_value variable1 substitution

let rec apply_substitution substitution p2 =
match p2 with
((Constant _) as term) -> term
| ((Variable _) as term) ->
if binds substitution term then lookup_value term substitution else term
| (Compound (f, terms)) ->
Compound (f, (map (fun term -> apply_substitution substitution term)
terms))

let rec apply_substitution_to_clause substitution (p, term, terms) =
(p,
(apply_substitution substitution term),
(map (fun term -> apply_substitution substitution term) terms))

let rec member variable1 p =
match p with
[] -> false
| (variable2::set) ->
if same variable1 variable2 then true else member variable1 set

let rec union p1 set2 =
match p1 with
[] -> set2
| (element::set1) ->
if member element set2
then union set1 set2
else element::(union set1 set2)

let rec variables_in p =
match p with
(Constant _) -> []
| ((Variable _) as term) -> [term]
| (Compound (f, terms)) -> fold_left union [] (map variables_in terms)

let rec variables_in_clause (p, term, terms) =
union (variables_in term) (fold_left union [] (map variables_in terms))

let occurs variable term = member variable (variables_in term)

let rec unify p1 p2 =
match p1, p2 with
(Constant constant1), (Constant constant2) ->
if constant1=constant2 then Some [] else None
| ((Constant _) as term1), ((Variable _) as term2) -> Some [(term2, term1)]
| (Constant _), (Compound _) -> None
| ((Variable _) as term1), ((Constant _) as term2) -> Some [(term1, term2)]
| ((Variable _) as term1), ((Variable _) as term2) -> Some [(term1, term2)]
| ((Variable _) as term1), ((Compound _) as term2) ->
if occurs term1 term2 then None else Some [(term1, term2)]
| (Compound _), (Constant _) -> None
| ((Compound _) as term1), ((Variable _) as term2) ->
if occurs term2 term1 then None else Some [(term2, term1)]
| (Compound (function1, terms1)), (Compound (function2, terms2)) ->
(if function1=function2
then let rec loop p1 p2 substitution =
(match p1, p2 with
[], [] -> Some substitution
| (term1::terms1), (term2::terms2) ->
(match unify (apply_substitution substitution term1) (apply_substitution substitution term2) with
None -> None
| Some substitution1 ->
loop terms1 terms2 (substitution1@substitution))
| _, _ -> None)
in loop terms1 terms2 []
else None)

let map_indexed f l =
let rec loop p i =
match p with
[] -> []
| (h::t) -> (f h i)::(loop t (i+.(Base 1.0)))
in loop l (Base 0.0)

let alpha_rename clause offset =
apply_substitution_to_clause
(map_indexed
(fun variable -> (fun i -> (variable, (Variable (offset+.i)))))
(variables_in_clause clause))
clause

let rec proof_distribution term clauses =
let offset =
fold_left (fun x y -> if x<=y then y else x)
(Base 0.0)
(map (fun (Variable variable) -> variable)
(fold_left union
[]
(map variables_in_clause clauses)))
in fold_left ( @ )
[]
(map (fun clause ->
let (p, term1, terms) = alpha_rename clause offset
in let rec loop p substitution terms =
match substitution with
None -> []
| Some substitution ->
match terms with
[] -> [(p, substitution)]
| term::terms ->
fold_left ( @ )
[]
(map (fun (p1, substitution1) ->
loop (p*.p1)
(Some (substitution@substitution1))
terms)
(proof_distribution
(apply_substitution substitution term)
clauses))
in loop p (unify term term1) terms)
clauses)

let likelihood substitution_distribution =
fold_left ( +. ) (Base 0.0) (map (fun (p, _) -> p) substitution_distribution)

let example _ =
(fun [p0; p1] ->
let clauses = [(p0, (Compound (make_p, [(Constant 0)])), []);
(((Base 1.0)-.p0),
(Compound (make_p, [(Variable make_x)])),
[(Compound (make_q, [(Variable make_x)]))]);
(p1, (Compound (make_q, [(Constant 1)])), []);
(((Base 1.0)-.p1),
(Compound (make_q, [(Constant 2)])),
[])]
in fold_left ( *. )
(Base 1.0)
(map (fun observation ->
likelihood
(proof_distribution
(Compound (make_p,
[(Constant observation)]))
clauses))
[0; 1; 2; 2]))
[(Base 0.5); (Base 0.5)]
(Base 1000.0)
(Base 0.1))

let _ =
(let rec loop i result =
if i<=(Base 0.0) && (Base 0.0)<= i
then result
else let ([p0; p1], _, _) = example ()
in loop (i-.(Base 1.0)) [(write_real p0); (write_real p1)]
in loop (Base 1000.0) [(Base 0.0); (Base 0.0)]; 0)
```

Generated by GNU enscript 1.6.4.