Add text challenges for end of chapter 5

text-challenges

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+Chapter 5, challenge 1:
+Earlier, I said that the | , * , and + forms we added to our grammar metasyntax
+were just syntactic sugar. Take this grammar:
+
+expr → expr ( "(" ( expr ( "," expr )* )? ")" | "." IDENTIFIER )+
+	| IDENTIFIER
+	| NUMBER
+
+Produce a grammar that matches the same language but does not use any of the notational sugar.
+
+solution:
+expr -> IDENTIFIER
+expr -> NUMBER
+expr -> expr callOrIndex
+
+callOrIndex -> "." IDENTIFIER
+callOrIndex -> "(" call ")"
+
+call ->
+call -> expr
+call -> expr callListEnd
+
+callListEnd -> 
+callListEnd -> "," expr precedingCommaCall
+
+
+The grammar here clearly describes a number, or an identifier to a number, or a
+function call, or a structure access
+
+Chapter 5, challenge 2:
+The Visitor pattern lets you emulate the functional style in an object-oriented
+language. Devise a complementary pattern for a functional language. It should let
+you bundle all of the operations on one type together and let you define new types
+easily.
+(SML or Haskell would be ideal for this exercise, but Scheme or another Lisp works
+as well.)
+
+solution:
+Here, we're supposed to be able to define a new type that "inherits" an
+existing one and bundle all the function implementations on that type together.
+We could simply write the functions by specific type in one place, since Haskell is just that flexible, but that doesn't guarrantee we wrote the needed functions.
+Another thing we could do is to put all necessary functions in a single structure, and define a type for this structure, for example if our supertype is Expr, with functions like "printInStr", "execute" and "optimize", our function bundle would look like:
+data ExprFuncs a = ExprFuncs (a -> str) (a -> IO ()) (a -> Expr)