Reasoning about Programming Languages in a Functional Manner

Jack Waugh — 2001-05-31 14:54:39

The group blurb says, among other things, "In short, concatenative 

languages behave in a way [that] looks imperative (like C or Perl), 

but can be reasoned about in a functional manner (like ML or 

Haskell).".



What is one characteric of Joy, ML, and Haskell that makes it 

possible to reason about them in a way that isn't possible with, say, 

C?



C is based on function composition, denoted by the ";" operator.  

Each C "statement" denotes a function in one parameter to produce one 

result.  In all cases, the type of the parameter and that of the 

result is "execution state".  An execution state includes a stack, an 

indexed memory space, open files, the system clock, the mental states 

of the users, the phase of the moon, etc.  Since the result of a 

function has the same type as the parameter and this type is the same 

for all functions in the language, we can readily construct 

compositions of any of the functions. . . .