Conversion of values to readable Strings.
Minimal complete definition: showsPrec or show.
Derived instances of Show have the following properties, which
are compatible with derived instances of Text.Read.Read:
 The result of show is a syntactically correct Haskell
expression containing only constants, given the fixity
declarations in force at the point where the type is declared.
It contains only the constructor names defined in the data type,
parentheses, and spaces. When labelled constructor fields are
used, braces, commas, field names, and equal signs are also used.
 If the constructor is defined to be an infix operator, then
showsPrec will produce infix applications of the constructor.
 the representation will be enclosed in parentheses if the
precedence of the toplevel constructor in x is less than d
(associativity is ignored). Thus, if d is 0 then the result
is never surrounded in parentheses; if d is 11 it is always
surrounded in parentheses, unless it is an atomic expression.
 If the constructor is defined using record syntax, then show
will produce the recordsyntax form, with the fields given in the
same order as the original declaration.
For example, given the declarations
infixr 5 :^:
data Tree a = Leaf a  Tree a :^: Tree a
the derived instance of Show is equivalent to
instance (Show a) => Show (Tree a) where
showsPrec d (Leaf m) = showParen (d > app_prec) $
showString "Leaf " . showsPrec (app_prec+1) m
where app_prec = 10
showsPrec d (u :^: v) = showParen (d > up_prec) $
showsPrec (up_prec+1) u .
showString " :^: " .
showsPrec (up_prec+1) v
where up_prec = 5
Note that rightassociativity of :^: is ignored. For example,
 show (Leaf 1 :^: Leaf 2 :^: Leaf 3) produces the string
"Leaf 1 :^: (Leaf 2 :^: Leaf 3)".
  Methods   :: Int  the operator precedence of the enclosing
context (a number from 0 to 11).
Function application has precedence 10.
 > a  the value to be converted to a String
 > ShowS   Convert a value to a readable String.
showsPrec should satisfy the law
showsPrec d x r ++ s == showsPrec d x (r ++ s)
Derived instances of Text.Read.Read and Show satisfy the following:
 (x,"") is an element of
(Text.Read.readsPrec d (showsPrec d x "")).
That is, Text.Read.readsPrec parses the string produced by
showsPrec, and delivers the value that showsPrec started with.

   A specialised variant of showsPrec, using precedence context
zero, and returning an ordinary String.
   The method showList is provided to allow the programmer to
give a specialised way of showing lists of values.
For example, this is used by the predefined Show instance of
the Char type, where values of type String should be shown
in double quotes, rather than between square brackets.

  Instances  Show Bool  Show Char  Show Double  Show Float  Show Int  Show Int8  Show Int16  Show Int32  Show Int64  Show Integer  Show Ordering  Show Word  Show Word8  Show Word16  Show Word32  Show Word64  Show ()  Show TyCon  Show TypeRep  Show ArithException  Show ErrorCall  Show SomeException  Show IOException  Show Lexeme  Show IOMode  Show SeekMode  Show CUIntMax  Show CIntMax  Show CUIntPtr  Show CIntPtr  Show CTime  Show CClock  Show CSigAtomic  Show CWchar  Show CSize  Show CPtrdiff  Show CDouble  Show CFloat  Show CULLong  Show CLLong  Show CULong  Show CLong  Show CUInt  Show CInt  Show CUShort  Show CShort  Show CUChar  Show CSChar  Show CChar  Show GeneralCategory  Show HashData  Show Dynamic  Show IntPtr  Show WordPtr  Show BufferMode  Show HandleType  Show Handle  Show IOErrorType  Show ExitCode  Show ArrayException  Show AsyncException  Show AssertionFailed  Show Deadlock  Show BlockedIndefinitelyOnSTM  Show BlockedIndefinitelyOnMVar  Show BlockedIndefinitely  Show BlockedOnDeadMVar  Show Fd  Show CRLim  Show CTcflag  Show CSpeed  Show CCc  Show CUid  Show CNlink  Show CGid  Show CSsize  Show CPid  Show COff  Show CMode  Show CIno  Show CDev  Show ThreadStatus  Show BlockReason  Show ThreadId  Show NestedAtomically  Show NonTermination  Show NoMethodError  Show RecUpdError  Show RecConError  Show RecSelError  Show PatternMatchFail  Show FD  Show HandlePosn  Show Fixity  Show ConstrRep  Show DataRep  Show Constr  Show DataType  Show Any  Show All  Show Timeout  Show Version  Show Exception  Show a => Show [a]  Integral a => Show (Ratio a)  Show (Ptr a)  Show (FunPtr a)  Show a => Show ([::] a)  Show a => Show (Maybe a)  Show (ForeignPtr a)  Show a => Show (Last a)  Show a => Show (First a)  Show a => Show (Product a)  Show a => Show (Sum a)  Show a => Show (Dual a)  RealFloat a => Show (Complex a)  HasResolution a => Show (Fixed a)  Show (a > b)  (Show a, Show b) => Show (Either a b)  (Show a, Show b) => Show (a, b)  Show (ST s a)  (Ix a, Show a, Show b) => Show (Array a b)  (Show a, Show b, Show c) => Show (a, b, c)  (Show a, Show b, Show c, Show d) => Show (a, b, c, d)  (Show a, Show b, Show c, Show d, Show e) => Show (a, b, c, d, e)  (Show a, Show b, Show c, Show d, Show e, Show f) => Show (a, b, c, d, e, f)  (Show a, Show b, Show c, Show d, Show e, Show f, Show g) => Show (a, b, c, d, e, f, g)  (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h) => Show (a, b, c, d, e, f, g, h)  (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i) => Show (a, b, c, d, e, f, g, h, i)  (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j) => Show (a, b, c, d, e, f, g, h, i, j)  (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k) => Show (a, b, c, d, e, f, g, h, i, j, k)  (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l) => Show (a, b, c, d, e, f, g, h, i, j, k, l)  (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l, Show m) => Show (a, b, c, d, e, f, g, h, i, j, k, l, m)  (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l, Show m, Show n) => Show (a, b, c, d, e, f, g, h, i, j, k, l, m, n)  (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l, Show m, Show n, Show o) => Show (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) 

