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a counter proposal

This page is part of the web mail archives of SRFI 10 from before July 7th, 2015. The new archives for SRFI 10 contain all messages, not just those from before July 7th, 2015.

To use the proposed read-time evaluation in a program the program
would have to be in two parts.  The first part defines the read-time
constructors and then loads a file containing the second part.  The
second part can use `#,' to call constructors defined in the first
part.  This is a very clumsy mechanism.  I could get the same effect
in vanilla R5RS, with much more power and flexibility, by using EVAL
and an extensible reader:

  (define my-reader (make-reader ...))

  (eval (my-reader filename) some-environment)

This two-phase evaluation is unnecessary.  Using `#,' in a program
has two effects: it causes side effects to occur at read time and it
ensures that a form is evaluated only once.  The first has questionable
utility and semantics.  The second is already available in R5RS as
`delay' and `force'.  The only thing missing is a concise notation.
Why not have


read as

  (force (delay (...)))

just as `(...) reads as (quasiquote ...)?  This avoids the need to
preregister constructors and it preserves the separation between
syntax and semantics.  A program can be evaluated in one fell swoop.

                                      -Richard Kelsey.