Discussion:
ML: psychological basis of language ranking?
(too old to reply)
A***@gmail.com
2012-10-16 13:13:32 UTC
Permalink
What does Harper mean?
I'll try to interpret this first/easier one, my self:
]Object-oriented programming is eliminated entirely from the
]introductory curriculum, because it is both anti-modular and
]anti-parallel by its very nature, and hence unsuitable for a modern
]CS curriculum.
Does he mean, that since the essence of OO is that objects
are defined [hence dependant on] by their ancestor, knowledge
about an object can't be decoupled from knowledge about its
ancestors?

Which leads into my main topic: we need to STATE our top-goal
for computer-languages; which surely [like all else in life] is to
get the best cost::benefit ratio. The cost/pain comes largely from
having to remember and be-concerned-about stuff.

So is he saying, that the cost for OO comes from the need to
be-concerned-about the ancestors?

Yes, for me, the freedon to NOT be-concerned-about
side issues is a MASSIVE advantage for any programming
system. And the ability to 'pipe/data-transform' sequentially
like forth, and at tested/confirmed stageN not to need to
be-concerned-about stageN-2.

Does ML support such a [concatenative] style?

Where's the literature about the psychological basis of computer
language design, instead of vague implications of 'why you like it'?

====> Then in
http://existentialtype.wordpress.com/tag/type-theory/
he writes: [in my simplified non-LaTex notation]
In languages we have the fundamental concept of a typing judgement, written
x1:A1,...xn:An => M:A
stating that M is an expression of type A involving variables xi of type Ai.
That's OK.
x:A => x:A
y:B => N:C x:A => M:B
-----------------------
x:A => [M/y]N:C
We may think of the variables as names for "libraries", in which
case the first states that we may use any library we wish, and the
second states closure under "linking" (as in the Unix tool ld or its
relatives), with [M/x]N being the result of linking x in N to the
library M .
Let's try to unpick that, in steps:
y:B => N:C
means N is an expression of type C involving variable y of type B
x:A => M:B
means M is an expression of type B involving variable x of type A

By `"linking" (as in the Unix tool ld)`, does he mean 'replace the
expression, with the code-which-implements it'?

What is his main point?

== TIA.
Torben Ægidius Mogensen
2012-10-19 07:58:34 UTC
Permalink
Post by A***@gmail.com
What does Harper mean?
]Object-oriented programming is eliminated entirely from the
]introductory curriculum, because it is both anti-modular and
]anti-parallel by its very nature, and hence unsuitable for a modern
]CS curriculum.
Does he mean, that since the essence of OO is that objects
are defined [hence dependant on] by their ancestor, knowledge
about an object can't be decoupled from knowledge about its
ancestors?
I don't think so. Objects are anti-paralllel because the fundamental
operation on modules is reading and updating storage local to the
object. I'm not sure what in particular makes him call them
anti-modular, but it might be for much the same reason: If there is
local mutable state in objects, you can't compose them freely, as a use
of the object in one place can affect another use of the same object in
another place in a way that you can't predict from its interface.
Post by A***@gmail.com
Yes, for me, the freedon to NOT be-concerned-about
side issues is a MASSIVE advantage for any programming
system. And the ability to 'pipe/data-transform' sequentially
like forth, and at tested/confirmed stageN not to need to
be-concerned-about stageN-2.
Does ML support such a [concatenative] style?
If I understand you correctly, it does. Function composition is natural
and easy in ML.
Post by A***@gmail.com
====> Then in
http://existentialtype.wordpress.com/tag/type-theory/
he writes: [in my simplified non-LaTex notation]
In languages we have the fundamental concept of a typing judgement, written
x1:A1,...xn:An => M:A
stating that M is an expression of type A involving variables xi of type Ai.
That's OK.
x:A => x:A
y:B => N:C x:A => M:B
-----------------------
x:A => [M/y]N:C
We may think of the variables as names for "libraries", in which
case the first states that we may use any library we wish, and the
second states closure under "linking" (as in the Unix tool ld or its
relatives), with [M/x]N being the result of linking x in N to the
library M .
y:B => N:C
means N is an expression of type C involving variable y of type B
x:A => M:B
means M is an expression of type B involving variable x of type A
By `"linking" (as in the Unix tool ld)`, does he mean 'replace the
expression, with the code-which-implements it'?
What is his main point?
The main point is that types act as contracts: If you replace a variable
of type B with an expression of type B, this will not yield typpe errors
and the type of the surrounding expression should not change by this
exchange. Basically, An expression of type B has the same type in every
context (assuming free variables, in this case x, do not change their
type in the different contexts).

Torben

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