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From: Panicz Maciej Godek <>
Subject: Type information seems to be erased in macros
Date: Wed, 29 Dec 2021 23:12:37 +0100	[thread overview]
Message-ID: <> (raw)

I have defined a macro:

(define-syntax-rule (with-translation screen (x y) . actions)
  (let ((x! x)
        (y! y))
    (screen:translate! x! y!)
    (let ((result (begin . actions)))
      (screen:translate! (- x!) (- y!))

which (presumably) operates on Screen interface, which provides translate!

I use it in a context which makes it clear that the type of the first
argument passed to with-translation is Screen:

(define (draw! object #!optional (screen::Screen (current-screen)))::Extent
  (with-translation screen (left top) ...)

However, when I import (to the REPL) a module containing this code, I get
the following complaint near the use of the with-translation macro:

warning - no known slot 'translate!' in java.lang.Object

Does the macro system erase type information from objects?

If I add explicit casts in the macro, is it likely to cause some
performance penalty?

             reply	other threads:[~2021-12-29 22:12 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-29 22:12 Panicz Maciej Godek [this message]
2021-12-29 23:30 ` Per Bothner
2021-12-30  8:52   ` Panicz Maciej Godek

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