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Re: [Chicken-users] case vs. eq? - just curious ....

From: Matt Welland
Subject: Re: [Chicken-users] case vs. eq? - just curious ....
Date: Fri, 2 Mar 2012 18:57:56 -0700

On Fri, Mar 2, 2012 at 5:04 PM, Jim Ursetto <address@hidden> wrote:
eqv?, to be exact.  Your case statement works fine for me, with for example (comp->text '=).  (eq? comp =) compares against the value of the procedure =, whereas the case compares against the symbol =.  So you are doing two different comparisons.

I'm trying to convert a comparison operator to the equivalent text. These are not symbols. I think case treats the target list as if it was created with a quote: '(>). Thus things are all symbols in the list and the eqv? returns false.

> (case > ((>) "yup")(else "nope"))
> (cond ((eqv? > >) "yup")(else "nope"))

The cond does what I need just fine, I just didn't understand why case didn't also work.

Is there a more schemeish way to convert any of the operators to the text representation?

(define gt >)
(op->string gt)
 => ">"

You can use ,x (case ...) at the REPL to see what the case expands to.

Fake edit: Kon said this more succinctly than I did.

On Mar 2, 2012, at 5:52 PM, Matt Welland wrote:

I expected this to work:

(define (comp->text comp)
  (case comp
   ((=)    "=")
   ((>)    ">")
   ((<)    "<")
   ((>=)  ">=")
   ((<=)  "<=")
   (else "unk")))

But had to convert to a cond with (eq? comp =) etc...

I thought case was supposed to use eq? to do the compare?

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