git @ Cat's Eye Technologies Fountain / 79bf574
Check that all choices on the Alt have a precondition. Chris Pressey 1 year, 7 months ago
2 changed file(s) with 29 addition(s) and 19 deletion(s). Raw diff Collapse all Expand all
+2
-4
doc/Definition-of-Fountain.md less more
244244 Goal ::= "f" | <. a = 0 .> "o";
245245 ???> No pre-condition
246246
247 (This one's not quite right yet.)
248
249 > Goal ::= (<. a = 0 .> "f") | "o";
250 > ???> No pre-condition
247 Goal ::= (<. a = 0 .> "f") | "o";
248 ???> No pre-condition
251249
252250 But if all choices of the Alt have constraints, we are able to select the one
253251 that fulfills the constraints.
+27
-15
src/Language/Fountain/Generator.hs less more
00 module Language.Fountain.Generator (constructState, generateFrom, obtainResult) where
1
2 import Data.Maybe (mapMaybe)
13
24 import Language.Fountain.Grammar
35 import Language.Fountain.Constraint
1921 -- Alt choices need preconditions because in generating, unlike parsing,
2022 -- we need some guidance of which one to pick
2123 --
22 getPreCondition :: Expr -> Expr -> Constraint
23 getPreCondition alts (Seq (x:xs)) = getPreCondition alts x
24 getPreCondition alts (Constraint c) = c
25 getPreCondition alts x = error ("No pre-condition present on this Alt choice: " ++ (show alts) ++ " => " ++ (show x))
24 getPreCondition :: Expr -> Maybe Constraint
25 getPreCondition (Seq (x:xs)) = getPreCondition x
26 getPreCondition (Constraint c) = Just c
27 getPreCondition x = Nothing
28
29 missingPreConditions choices =
30 mapMaybe (\x -> case getPreCondition x of
31 Just _ -> Nothing
32 Nothing -> Just x
33 ) choices
2634
2735
2836 gen :: Grammar -> GenState -> Expr -> GenState
3745 -- We look at all the choices; each should start with a pre-condition
3846 -- determining whether we can select it; and we should narrow down our
3947 -- choices based on that. (Then pick randomly? Or insist deterministic?)
40 gen g st@(Generating str store) alts@(Alt s) =
41 let
42 preConditionedAlts = map (\x -> (getPreCondition alts x, x)) s
43 applicableAlts = filter (\(c, x) -> canApplyConstraint c store) preConditionedAlts
44 in
45 genAlt g st applicableAlts where
46 genAlt g st [] = Failure
47 genAlt g st ((_, e) : rest) =
48 case gen g st e of
49 Failure -> genAlt g st rest
50 st' -> st'
48 gen g st@(Generating str store) (Alt choices) =
49 case missingPreConditions choices of
50 missing@(_:_) ->
51 error ("No pre-condition present on these Alt choices: " ++ (show missing))
52 [] ->
53 let
54 preConditionedChoices = map (\x -> (getPreCondition x, x)) choices
55 applicableChoices = filter (\(Just c, x) -> canApplyConstraint c store) preConditionedChoices
56 in
57 genAlt g st applicableChoices where
58 genAlt g st [] = Failure
59 genAlt g st ((_, e) : rest) =
60 case gen g st e of
61 Failure -> genAlt g st rest
62 st' -> st'
5163
5264 gen g state (Loop l postconditions) =
5365 genLoop g state l (assertThereAreSome postconditions) where