[clean-list] Help Please: Beginner to Clean.. Console I/O

[Jerzy Karczmarczuk]

Khurram Khan:

    We believe that probably Clean user-guides are written for people
    who have some previous knowledge of functional programming (...)


Yes, I believe you are right. If you and your friends have problems with 
the *understanding* of the IO issues, please, instead of following the 
advice to read about some syntactic structures in Clean, look into some 
general articles on functional programming, purity and laziness, 
otherwise you will be constantly perplexed (which is not so bad after 
all). The first thing to understand is the IMPLICATIONS of the fact that 
a functional program does not modify your data structures.

    we are also aware of the fact that by doing regular I/O operations
    in functional programming might defeat the purpose of writing a
    program in a functional language because it will then resemble
    procedural programming style,(...)


This is not exact. Psychologically, perhaps (that's why in Haskell we 
have the "do" block), but the functional IO is  ... functional. Even the 
global environment of your program has a functional avatar. That's why 
you write:

(console, wrld) = stdio wrld

A file (here: the console) must be picked out of this environment (the 
class: FileSystem, whose instance is the World, a possible parameter of 
Start). But the referential transparency forbids you to write, say : 
console = stdio(), or console=Stdio(world)  since making a link to your 
file system changes the world. So, you create a new world, and the 
"uniqueness" property of Clean ensures that you cannot reach the 
previous one, it is "destroyed". So, you may reuse its name. Of course 
"in reality" (btw., somebody knows what is "reality"?), this reduces to 
the modification of the unique world exemplar.
And the Ship Sails On.
To read a line from the console, you write

(line, console) = freadline console

Since reading modifies the console, its "new instantiation" is passed as 
a part of the result. If you want to write something, you have to write

console = fwrites "And the Ship Sails On\n" console

and not just:fwrites "something". This IS SIMPLE, you need only to keep 
in your mind, that nothing is implicit, under the rug, and nothing is 
"modified", rather "recreated".

I believe that we could help you in a more efficient way, if you pose 
some concrete questions, detailed, and "atomic".

All the best

Jerzy Karczmarczuk

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