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Define small-step semantics for assignment.

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Rob Rix 2017-04-05 21:16:09 -04:00
parent bca1bf08d8
commit ddba2b53cd
1 changed files with 15 additions and 0 deletions
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15
src/Language/Ruby/Syntax.hs
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@ -74,3 +74,18 @@ data Node grammar = Node { nodeSymbol :: grammar, nodeContent :: ByteString }
-- | An abstract syntax tree.
type AST grammar = Rose (Node grammar)
stepAssignment :: Eq grammar => Assignment grammar a -> [AST grammar] -> Maybe ([AST grammar], a)
stepAssignment = iterFreer (\ assignment yield nodes -> case nodes of
[] -> Nothing
Rose Node{..} children : rest -> case assignment of
Rule symbol subRule ->
if symbol == nodeSymbol then
yield subRule nodes
else
Nothing
Content -> yield nodeContent rest
Children each -> yield (snd (forEach children)) rest
where forEach rest = case stepAssignment each rest of
Just (rest, x) -> let (rest', xs) = forEach rest in (rest', x : xs)
Nothing -> (rest, [])
Fail -> Nothing) . fmap ((Just .) . flip (,))