Re: expressions vs. statements

["S. Alexander Jacobson" <address@hidden>]

Here is another reason for statement/expression dichotomy (related to the
return issue):

Statements express evaluation order in a more readable manner than
expressions.  Therefore you want statements if most of your functions have
side-effects, and you want expressions if most of your functions take an
argument and return a value and you are more indifferent to evaluation
order.

The designers of Haskell recognized this when they gave Monads a separate
syntax from the rest of the language.  In an expression like this:

result= h (g (f x))

Functions are evaluated in the opposite order from how they appear.  In
contrast, monad syntax (used for IO and sideeffects), looks like this:
result= f x >>= g >>= h

or like this:
result = do
	  f x
	  g
	  h
	  return

(My haskell is somewhat rusty, so someone here can correct me)
Functions appear in the order they are executed.

The general point:

Statements expres evaluation order in a more readable manner than
expressions.

-Alex-

___________________________________________________________________
S. Alexander Jacobson                   i2x Media
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