[erlang-questions] Simple Erlang Recommendation (last returned value)

Andreas Hillqvist <>
Tue Jul 29 08:42:45 CEST 2008


Small note:

You shoule be able to write:
    lists:foldl(fun queue:add/2, queue:new(), [joe, mike]).

If you would like to save keystrokes. ;-)


Kind regards
Andreas Hillqvist

2008/7/28, Berlin Brown <>:
>
>
> On Jul 28, 6:10 am, "Jesper Louis Andersen"
> <> wrote:
> > On Mon, Jul 28, 2008 at 2:47 AM, Richard A. O'Keefe <> wrote:
> >
> > > Also, functional language with explicit 'let' allow
> > >        let val x = 1 in
> > >        let val x = x + 1 in
> > >        x+1 end end
> > > (SML) or
> >
> > This is infected with Ocaml syntax style :) The SML way would be:
> >
> > let
> >   val x = 1
> >   val x = x + 1
> > in
> >   x + 1
> > end
> >
> > But at least one SML compiler has a warning with this style of coding
> > since you are shadowing the 'x' value and it quickly becomes rather
> > hard to follow what def-point is meant for each use (To the
> > non-SML'ers, let .. in .. end works somewhat like Schemes LET*). With
> > SML beginners, you often see "imperative" style code where the
> > let-blocks evaluation order is used to force imperative code while a
> > more functional solution is apparent to the experienced.
> >
> > What the let-binding tends to be used for is to declare a number of
> > local functions (Which may be recursive) and then gradually combine
> > these into more advanced functions, of which the last is called in the
> > body of the binding.
> > _______________________________________________
> > erlang-questions mailing list
> > ://www.erlang.org/mailman/listinfo/erlang-questions
>
> Thanks for all of the responses.
>
> I think this is the best solution for what I am doing.
>
> lists:foldl(
>   fun(X, Last_value) -> queue:add(X, Last_value) end,
>   queue:new(),
>   [joe, mike]).
>
> -------------------
>
> There are a couple of things that I wanted to make clear.  I did NOT
> want to change the mutability aspect of Erlang, as many have
> suggested, it goes to the core of Erlang and functional programming.
> And ideally what I suggested was more from "stack/functional" based
> languages like Factor or Forth not so much imperative languages like
> Java/C++.
>
> I as assuming there was a call stack or some internal mechanism in
> Erlang that keeps track of the result of the last expression and maybe
> there is a way to "dup"licate that expression or something similar.
>
> In a stack oriented language, you push expression onto the stack and
> perform operations against values that are on the stack.   There are
> built in functions to duplicate, copy values on the stack. The
> following code is equivalent in "Factor" a forth based language.
> Square the values on the stack.
>
> 3 3 * .
>
> Or
>
> 3 dup * .
>
> Dup = duplicates the value on the stack.
>
> ================
>
> Essentially, I was wishing there was a similar erlang function to do
> something which might save keystrokes.
>
> Q1 = queue(dog, NewQ),
> Q2 = queue(dog, Q1),
> Q3 = queue(dog, Q2)
> ...
>
> Q1 = queue(dog, NewQ),
> queue(dog, erlang:dup()),
> queue(dog, erlang:dup())
> ...
> where dup = return result from last expression.
>
> ...
> ================
>
> And I don't totally understand how erlang expressions are evaluated so
> it may not make sense at all in Erlang.  For example, with Erlang's
> pattern matching, internally expressions may not be evaluated in such
> a routine by routine fashion as they may be in imperative languages.
>
> Thanks and this look like a good discussion.
> _______________________________________________
> erlang-questions mailing list
> 
> http://www.erlang.org/mailman/listinfo/erlang-questions
>



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