January 17 2007 水曜日

　　The strictness flag !, can only appear in data declarations.  It cannot be used in other type signatures
or in any other type definitions.  There is no corresponding way to mark function arguments as being strict,
although the same effect can be obtained using the seq or !$functions.

  Strictness
flags may be used to address memory leaks: structures retained by the garbage collector but no
longer necessary for computation.  Laziness is one of the fundamental properties of Haskell and adding strictness
fl
ags may lead to hard to find infinite loops or have other unexpected consequences.

  Actions are sequenced using an operator that has a rather cryptic name: >>= (or 'bind').  Instead of using
this operator directly, we choose some syntactic sugar, the do notation, to hide these sequencing operators
under a syntax resembling more conventional languages.  The do notation can be trivially expanded to >>=.