[Haskell-cafe] Pattern match failure

[Jackm139]

I'm trying to write a function to recognize a context free grammar, but I
keep getting pattern match failure errors. This is what I have:

data Grammar c = Brule c c c | Rule c c

gez = [(Brule 'S' 'p' 'D'),(Brule 'D' 't' 'E'),(Rule 'E' 'j')]

recog :: String -> String -> [Grammar Char] -> Bool
recog a b list = case list of
	[Brule x y z] -> if a == [x] then recog [z] b list else recog a b list
	[Rule x y] -> True


how can I solve this pattern matching error?

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