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Re: "subexpression"

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On 11/27/2015 08:02 PM, Stefan Ram wrote:
>   C uses the term »subexpression«, but does not define it.
> 
>   It is not easy to define »subexpression« on an elementary level.
> 
>   For example, in the web, one can find:
> 
>       »A subexpression is a part of an expression that is by
>       itself a correct expression.«
> 
>   By this, »2/3« would be a subexpression of »1/2/3«, but I
>   don't want this to be true.
> 
>   In the web, one can also find:
> 
>       »a subexpression is a part of an expression that
>       corresponds to a subtree in the parse tree«.
> 
>   That's better! So, »2/3« is /no/ subexpression in »1/2/3«,
>   because »1/2/3« is parsed as »(1/2)/3«.
> 
>   But can we explain »subexpression« to beginners who do
>   not know what a »parse tree« is?
> 
>   My first attempt was: »A subexpression is a part of a larger
>   expression that is an expression and can be replaced by its
>   value in the larger expression without changing the value of
>   the larger expression.«
> 
>   But by this definition, in »1/1/1«, the right »1/1« would be
>   a subexpression, because replacing it by its value does not
>   change the value of the full expression. So my first attempt
>   does not have all the desired properties.

A sub-expression of an expression is either one of it's own direct
operands, or recursively, one of it's operand's sub-expressions.

I don't claim that definition to be authoritative, but I think it
expresses correctly my understanding of the term, and I don't think it
conflicts with anything the standard says about sub-expressions.

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Re: "subexpression" James Kuyper <jameskuyper@verizon.net> - 2015-11-27 20:16 -0500
  Re: "subexpression" Keith Thompson <kst-u@mib.org> - 2015-11-27 19:42 -0800
    Re: "subexpression" Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-28 06:33 -0800
    Re: "subexpression" James Kuyper <jameskuyper@verizon.net> - 2015-11-28 10:21 -0500

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