Ensuring modifiable references within a backquoted template

• To: lgm%ihlpf.att.com@Riverside.SCRC.Symbolics.COM, slug%warbucks.ai.sri.com@Riverside.SCRC.Symbolics.COM
• Subject: Ensuring modifiable references within a backquoted template
• From: RWK@FUJI.ILA.Dialnet.Symbolics.COM (Robert W. Kerns)
• Date: Mon, 7 May 90 14:16 EDT
• In-Reply-To: <9004231821.aa12329@mintaka.lcs.mit.edu>

    Date: Mon, 23 Apr 90 15:11 CDT
    From: lgm@ihlpf.att.com
    always yields the identical list structure.  On the other hand,
    applying the comma to a function call such as

	    `(A (B ,(IDENTITY NIL))

    indeed results in multiple, safely modifiable list structures.
    Can I depend on this behavior portably, or could a Common Lisp
    implementation thwart my intent by "intelligently"
    constant-folding (IDENTITY NIL) into NIL anyway?  If I were to
    locally declare IDENTITY to be NOTINLINE, would I then be "safe"
    (though slightly slower)?

I suggest using

(locally (declare (notinline copy-tree))
  `(A (B ,(COPY-TREE NIL))))

instead.  It's both less likely to be constant folding, and more
indicative of your actual intent.

• Ensuring modifiable references within a backquoted template
• From: KMP@STONY-BROOK.SCRC.Symbolics.COM (Kent M Pitman)

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