Re: Lisp's QUOTE and Mathematica's "Hold"

Jon Harrop wrote: 

i.e., Hold "sticks" with the expression, whereas QUOTE is just a signal
to the evaluator to pass its contents through unevaluated.  You can't
build something as simple as QUOTE in Mathematica because the evaluator
will keep evaluating until it stops changing - the CL QUOTE would be a
noop in the Mathematica evaluator.



You can see Hold in Mathematica but not QUOTE in Lisp but isn't that more a
function of the pretty printer rather than the evaluation?


No, it's a function of it not being there.

A   => <the value of A>
'A  => A
''A => 'A a.k.a. (QUOTE A)

This distinction is very significant, because QUOTE only 'protects' against one round of evaluation.

(EVAL A)   => <the result of evaluating the value of A>
(EVAL 'A)  => <the value of A>
(EVAL ''A) => A

In a hypothetical Mathematica-like dialect of Lisp,

A          => <the value of A>
'A         => <the value of A>
''A        => <the value of A>
(EVAL A)   => <the value of A>
(EVAL 'A)  => <the value of A>
(EVAL ''A) => <the value of A>


Beyond that, evaluation is completely different. But just looking at QUOTE
and Hold, there is an uncanny resemblance.


If you ignore the name, syntax and behaviour.
.

Relevant Pages

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  • Re: Lisps QUOTE and Mathematicas "Hold"
    ... > Both QUOTE and Hold retain subexpressions in unevaluated form. ... >> to the evaluator to pass its contents through unevaluated. ... >> noop in the Mathematica evaluator. ...
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  • Re: Lisp Beginner question
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  • Re: Lisps QUOTE and Mathematicas "Hold"
    ... > Both QUOTE and Hold retain subexpressions in unevaluated form. ... >> to the evaluator to pass its contents through unevaluated. ... >> noop in the Mathematica evaluator. ...
    (comp.lang.lisp)
  • Re: Lisps QUOTE and Mathematicas "Hold"
    ... Both QUOTE and Hold retain subexpressions in unevaluated form. ... > to the evaluator to pass its contents through unevaluated. ... > noop in the Mathematica evaluator. ...
    (comp.lang.lisp)