World: r3wp

Just a terminological note: the strings you convert to REBOL expressions 
are not "mathematical equations". They are just mathematical expressions.

an equation has an = sign in the expression

BTW, there is an error in associativity:

>> parse-equation "3-3-3"
== [subtract 3.0 subtract 3.0 3.0]

(you need to take into account, that some operations are left-associative, 
while other operations may be right-associative)

The same error here:

>> parse-equation "3-3+3"
== [subtract 3.0 add 3.0 3.0]

Did you see http://www.rebol.org/view-script.r?script=supercalculator.r&sid=f4jz
(script start in the just last 20 lines)
instead of parse you can use "replace/all" and work evene better

Ladislav, thanks for your comments... I will have a closer look  
on this associativity issue.

MaxV. Yes, I have seen supercalculator but it crashes on simple expression 
like sqrt(1-3)/(1+4)...

MaxV sorry, my mistake... normal it crashes :)

But when i tried it, it fails on an expression... I do not remember 
which one...

MaxV: supercaclulator fails on 1/-(3+2)

regarding the supercalculator - it has wrong associativity as well

like parse-equation.r did yesterday btw :)

Ladislav... sorry, what should be the code returned?

in which case?

3-3+3

add subtract 3 3 3

Do you have an example where this would make a difference?

>> subtract 3.0 add 3.0 3.0
== -3.0

>> add subtract 3.0 3.0 3.0
== 3.0

I think, that counts as a difference

oups :)

Do you think that parsing reversal would fix the problem

not completely

you need to realize, that the ** operator is right-associative

I should review some basic math stuff :))

Ladislav... according to wiki, addition, subtraction, multiplication 
and division are left-assiciative... http://en.wikipedia.org/wiki/Operator_associativity

yes

Now that I take a paper and a pen... left-associativity is indeed 
natural :)

So natural that i forgot about the associativity when thinking on 
how to split an expression i successive blocks! So stupid!

:-D

Thanks for pointing this. Hopefully, I have been clever not to mark 
this version as 1.0.0 :)

I put my %evaluate.r script processing operators with different priorities 
and associativities to the

http://www.rebol.org/view-script.r?script=evaluate.r


as well, since I think there it will be more accessible to the public

Your script is so much more complicated :)... maybe why it works... 
Good idea to put on rebol.org!

A quick doc to show how to use it?

Much more complicated

 - do not forget it processes three different rule sets, each of which 
 uses different priorities and associativities.

How to use it: check the examples at the bottom

yes... the concept of "rule sets" is not straightforward :) what 
do you mean by this?

OK... very nice indeed! But can I use "unknown variable"

the rule sets are described in the comments to the SRA, STD and RLE 
functions

>> mold sra [3 - 3 + 3] translate
== "[subtract 3 add 3 3]"

>> mold std [3 - 3 + 3] translate
== "[add subtract 3 3 3]"

unknown variable
? you need to use the %use-rule.r script:

http://www.rebol.org/view-script.r?script=use-rule.r

I guess, that you actually want to use just the STD function

I will adopt your script! Impressive. But i am still wondering if 
with the strategy in my script it would be possible to implement 
associativity properly?

well, if you modify it appropriately, why not?

except, that it requires some care, since all the operators you use 
are left-associative, except for the exponentiation operator, which 
is right-associative

>> std [3 ** 3 ** 3] translate
== [power 3 power 3 3]

>> std [3 * 3 * 3] translate
== [multiply multiply 3 3 3]

THat's why parsing reversal and taking care of ** specifically might 
be a good start...

Parsing reversal does not help IMO, because you have to process both 
left- and right-associativity at the same time

Notice, that my script parses left to right

I think I found a way... see you later today (or tomorraow). Again, 
many thanks for your feedback and congrat for your impressive script

It was actually so easy to fix: 5 'append to change into 'insert... 
I still have to check this does not break anything before posting 
a new version on rebol.org.

Ladislav... thank you again for pointing this bug!