New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!

Xah Lee xahlee at gmail.com
Fri Mar 2 14:12:20 CET 2012


On Mar 1, 3:00 am, Kiuhnm <kiuhnm03.4t.yahoo.it> wrote:
> They did not make up the terminology, if that is what you are saying.
> The concepts of left and right associativity are well-known and accepted
> in TCS (Theoretical CS).


> Aho, Sethi and Ullman explain it this way in "Compilers: Principles,
> Techniques and Tools":
> "We say that the operator + associates to the left because an operand
> with plus signs on both sides of it is taken by the operator to its
> left. [...]"
> And they also show parse trees similar to the ones I wrote above.

how do they explain when 2 operators are adjacent e.g. 「3 △ 6 ▲ 5 」?

do you happen to know some site that shows the relevant page i can
have a look?

thanks.

 Xah

On Mar 1, 3:00 am, Kiuhnm <kiuhnm03.4t.yahoo.it> wrote:
> On 3/1/2012 1:02, Xah Lee wrote:
>
> > i missed a point in my original post. That is, when the same operator
> > are adjacent. e.g. 「3 ▲ 6 ▲ 5」.
>
> > This is pointed out by Kiuhnm 〔kiuhnm03.4t.yahoo.it〕 and Tim Bradshaw.
> > Thanks.
>
> > though, i disagree the way they expressed it, or any sense this is
> > different from math.
>
> They did not make up the terminology, if that is what you are saying.
> The concepts of left and right associativity are well-known and accepted
> in TCS (Theoretical CS).
>
> If you change the terminology, no one will understand you unless you
> provide your definitions every time (and then they may not accept them).
>
> Another way of saying that an operator is left-associative is that its
> parse tree is a left-tree, i.e. a complete tree where each right child
> is a leaf.
> For instance, (use a monospaced font)
>    1 + 2 + 3 + 4
> gives you this left-tree:
>        +
>      +   4
>    +   3
>   1 2
> while 1**2**3**4
> gives you this right-tree:
>    **
> 1    **
>     2    **
>         3  4
>
> Aho, Sethi and Ullman explain it this way in "Compilers: Principles,
> Techniques and Tools":
> "We say that the operator + associates to the left because an operand
> with plus signs on both sides of it is taken by the operator to its
> left. [...]"
> And they also show parse trees similar to the ones I wrote above.
>
> Kiuhnm



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