[plt-scheme] let vs parameterize?

Another difference between parameters and fluid-let: in a fluid-let
the values are not thread local, but in a parameter they are.

Robby

On 4/16/07, Carl Eastlund <cce at ccs.neu.edu> wrote:
> On 4/16/07, Yin-So Chen <yinso.chen at gmail.com> wrote:
> > What is the difference between using let vs parameterize?
>
> Let operates on bindings.  It creates a new name and binds it to a
> value.  This affects code directly within the let-body that refers to
> the same name, providing it is not bound again ("shadowed") inside the
> let.
>
> Parameterize operates on parameters, which are values.  It takes an
> existing parameter and makes it return a different value during the
> execution of the body of the parameterize.  This affects any code
> called during that execution, even if it's in a different function,
> module, whatever, so long as it uses the same parameter value.
>
> > It seems that one can use let to manipulate parameter objects (at least
> > scheme doesn't forbid it) - any issues with using it?
>
> Let does not manipulate values at all.  It just binds names to
> existing values.  It never changes values or their contents.
>
> >  How do I know whether or not something is a parameter versus a variable?
>
> You could ask the same thing about numbers vs variables, or strings vs
> variables.  A variable is a name for a value.  That value might be
> anything: number, string, list, parameter, etc.  But you should be
> careful never to confuse the name with what it refers to.
>
> And in response to the followup email: fluid-let, like let, operates
> on variables (names), not values.  Hence it would not be an
> "extension" to make it work on parameters.  If you give the name of a
> parameter to fluid-let, it will change which parameter that name
> refers to, not the contents of the current parameter.
>
> --
> Carl Eastlund
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