Some crude snippets from a Pascal-C (I never could decide) self-educational compiler/toy I wrote a while ago (in Haskell):

    -- a parser function that matches on { ... } returning ... 
    -- can be combined with other parsers 
    braces = (symbol "{") `between` (symbol "}") 
    ...
    -- a statement is a controlFlow or a declaration or an assignment
    statement = controlFlow <|> declaration <|> assignment

    -- a block is either 1 or more statements surrounded by { ... }
    -- or a single statement.
    block = (braces $ many statement) <|> statement
    ...
    -- An expression is a number, or a variable, or a binary operation
    -- derive functionality to print and test equality of these values.
    data Expr = 
        Num Int
      | Var Variable
      | DualOp Op Expr Expr
      ...
      deriving (Show, Eq)
    ...
    foldConstants (DualOp Add (Num a) (Num b)) = Num (a + b)
    ...

Parser combinators (parser functions that take other parser functions and return more complex combined parser functions) with enough syntactic sugar can express BNF-like grammars directly as code. And ML-style list and pattern matching operations are very expressive for operating on the intermediate representation.