Binding symbols in stages
In order to do currying via C++ functions*), I might use something like an evaluator that evaluates an unbound symbol to itself. Is that possible? Translated into Scheme code, it corresponds to defining say (define add (lambda (x) (lambda (y) (+ x y by (define add1 (lambda (y) (+ x y))) and then (define add (lambda (x) ...)) Thus in two separate steps, where the unbound symbol x in the first expression is bound only in the second. I use now scm_eval(scm_list_3(scm_sym_lambda, x, y), scm_interaction_environment()) where x is a list of symbols and y an expression. Hans *) See the code at http://math.su.se/~haberg/guile/
Re: Binding symbols in stages
Hi Hans, On Sat 06 Mar 2010 10:03, Hans Aberg writes: > (define add1 (lambda (y) (+ x y))) > and then > (define add (lambda (x) ...)) > Thus in two separate steps, where the unbound symbol x in the first > expression is bound only in the second. If I understand you correctly, this is not possible in normal Scheme. (I say normal Scheme because you can build your own interpreter for another kind of Scheme within Guile, one with dynamic binding, say.) The way to leave a bound identifier unbound is precisely to wrap it in a closure. For example to "delay binding" of Y and Z in: (lambda (x) (+ x y z)) you need wrap the expression in a lambda: (lambda (y z) (lambda (x) (+ x y z))) Which seems to be what you're trying to get away from, though I don't know why. Hope this helps, Andy -- http://wingolog.org/
Re: Binding symbols in stages
On 6 Mar 2010, at 12:13, Andy Wingo wrote:
(define add1 (lambda (y) (+ x y)))
and then
(define add (lambda (x) ...))
Thus in two separate steps, where the unbound symbol x in the first
expression is bound only in the second.
If I understand you correctly, this is not possible in normal Scheme.
I suspected that; thanks for the confirmation.
(I
say normal Scheme because you can build your own interpreter for
another
kind of Scheme within Guile, one with dynamic binding, say.)
What do you have in your mind here?
The way to leave a bound identifier unbound is precisely to wrap it
in a
closure. For example to "delay binding" of Y and Z in:
(lambda (x) (+ x y z))
you need wrap the expression in a lambda:
(lambda (y z)
(lambda (x) (+ x y z)))
Which seems to be what you're trying to get away from, though I don't
know why.
I'm Scheme expressions as a part of the interface. So x >>= f
constructs (lambda (x) f). Now, if I want to create a function, I can
do that by
symbol x("x");
function1 inc = x >>= x + integer(2);
One option is to let the ">>=" operator evaluate the expression, and
hand that over to "inc", which then will hold a procedure.
But then there is a problem when doing a curried function:
symbol x("x"), y("y");
function2 add = x >>= y >>= x + y; //
Binds to the right.
Then if y >>= x + y evaluates (lambda (y) (+ x y)), one ends up on the
question I asked for: all attempts to use the symbol x in it will
produce an unbound variable error.
So suppose I just store the lambda expression produced by ">>=" in the
function class. Then scm_call_1() etc only acts on procedures. So I
have to evaluate f(x)
scm_primitive_eval(scm_list_2(f, x);
One drawback of this approach, I gather, is that the lambda expression
isn't evaluated into a procedure, which might be slow.
So yet another approach might be to let the function class evaluate
the expression into a procedure, and when a member f needs to be used
in an expression, restore it as such by (lambda x' (f x')), where x'
is an uninterned symbol.
Hans
Re: Binding symbols in stages
Typos, it should have been for the curried function type:
symbol x("x"), y("y");
function1 > add = x >>= y >>= x
+ y;
// Binds to the right.
Hans
(no subject)
I have a project which main purpose is to edit the cursor so that the program can write from right to left (arabic language) I downloaded the software from the website and the source for windows version wintexmacs-1.0.5-src.exe .I use microsoft visual studio 2008 after i tried to convert the existing project have been built with 4200 errors and thasn't work,then i saw that there is some requirements to install the guile library please i would be very thankful if you send me a detailed information on how to builth the program. any information that can help me in my project please . thanks-sorry for my bad english---
