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docs/lectures/compilers/04_functional_parsers.md

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+# Functional Parsers
+
+In our parser - there's a lot of repeated code and a lot of cases.
+
+
+
+Types of scanner and parser are very similar
+
+```haskell
+scanToken :: String  -> Maybe (Token, String)
+parseTerm :: [Token] -> Maybe (AST,  [Token])
+parseExp :: [Token]  -> Maybe (AST,  [Token])
+
+general :: [c] -> Maybe (a, [c])
+lessGeneral :: String -> Maybe (a, String)
+
+--remember :t string :: [char]
+-- [c] list of characters or tokens
+
+Parser a :: String -> [(a, String)]
+-- no maybe needed as failure is now returning an empty list
+--The parser of type a, we can now define generic functions that operate on a given type => less repeated code
+--This is an instance of a typeclass (monad yikes)
+```
+
+Do notation
+
+```haskell
+Parser a = String -> [(a, String)]
+
+symbol :: String -> Parser ()
+-- no need to define result, as all it does it succeed or fail
+
+exp :: Parser AST
+parseParenthesis :: Parser AST
+parseParenthesis = do symbol '('
+					t <- exp
+					symbol ')'
+					return t
+```
+