Evaluate string expression in MQL4 | Forex Factory

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Evaluate string expression in MQL4

  • #1
  • First Post: Nov 9, 2013 7:32pm Nov 9, 2013 7:32pm
MQL4 does not seem to have an equivalent of eval/evaluate function where you could enter a string expression like "A<B && C<D" or "1 + 2" so a call like eval("1 + 2") would return 3.

Does anyone have a working solution for this e.g. by importing this function from a dll file or something similar?

I am looking for a solution that does not require me to write/compile my own dll but rather importing a dll that has already been created or a function that someone (clearly brilliant individual) has already written using mql4. As far as I can tell, the typical Windows API dll files do not include this function but I could be wrong (which would be great since then it should be simple to import it).

Any suggestions welcome.

Aim
  • #2
  • Nov 10, 2013 4:13am Nov 10, 2013 4:13am
Quoting AimHigher
MQL4 does not seem to have an equivalent of eval/evaluate function where you could enter a string expression like "A<B && C<D" or "1 + 2" so a call like eval("1 + 2") would return 3. Does anyone have a working solution for this e.g. by importing this function from a dll file or something similar? I am looking for a solution that does not require me to write/compile my own dll but rather importing a dll that has already been created or a function that someone (clearly brilliant individual) has already written using mql4. As far as I can tell, the...

really?

what about

int Answer = 1 + 2;

or

if( A<B && C<D)
do this
  • #3
  • Nov 10, 2013 4:26am Nov 10, 2013 4:26am
Quoting MaxDoom
{quote} really? what about int Answer = 1 + 2; or if( A<B && C<D) do this
He wants some flaky calculator type setup that receives arbitrary input, in which case you need to be able to tokenize the input correctly and then properly handle precedence rules and deal with intermediate results and type-promoting.

If anyone wants to suggest that this should be easy, then good luck to you. You should be writing compilers.
Congratulations ScalaFX for coming out of the closet!
  • #4
  • Nov 10, 2013 4:42am Nov 10, 2013 4:42am
Quoting nubcake
{quote} He wants some flaky calculator type setup that receives arbitrary input, in which case you need to be able to tokenize the input correctly and then properly handle precedence rules and deal with intermediate results and type-promoting. If anyone wants to suggest that this should be easy, then good luck to you. You should be writing compilers.
lol, yes I missed the essence of that

still not too difficult to do but very time consuming and personally I would rather doing that kind of modelling outside MT.
  • #5
  • Nov 10, 2013 4:58am Nov 10, 2013 4:58am
Quoting MaxDoom
still not too difficult to do
Sure. Just a couple of if-then-else blocks and it's all done...

Have you ever attempted this? Maybe I should have deferred to your help when writing my toy'ish compiler and saved myself some time.
Congratulations ScalaFX for coming out of the closet!
  • #6
  • Nov 10, 2013 5:58am Nov 10, 2013 5:58am
Quoting nubcake
{quote} Sure. Just a couple of if-then-else blocks and it's all done... Have you ever attempted this? Maybe I should have deferred to your help when writing my toy'ish compiler and saved myself some time.
Yes I used to be programming in assembler before spreadsheets existed we used to do everything the hard way
  • #7
  • Nov 10, 2013 6:35am Nov 10, 2013 6:35am
Quoting MaxDoom
{quote} Yes I used to be programming in assembler before spreadsheets existed we used to do everything the hard way
Lies. Spreadsheets always existed.

In that case
Congratulations ScalaFX for coming out of the closet!
  • #8
  • Nov 10, 2013 7:20am Nov 10, 2013 7:20am
Quoting nubcake
{quote} Lies. Spreadsheets always existed. In that case
Yes of course the world was born with Microsoft and lotus. At least it must seem that way to people under 30
  • #9
  • Nov 10, 2013 8:49am Nov 10, 2013 8:49am
Wow, 7 replies without me even participating and true to general form here on FF and other forums, the first reply assumed the thread starter is an idiot.

Since Eval/Evaluate exists in several other programming languages (http://en.wikipedia.org/wiki/Eval), I though it was conceivable that someone had created/knew about a dll file that included the Eval function (e.g. by calling VBScript that has that function built it) and that such a dll could be accessed using #import in mql4.

I very well know that Eval isn't necessary (you can work around it) or a "pure" solution and can be flaky but since I was simply going to use if for some rudimentary testing and wanted to save development time, I figured that asking about it would cause no harm, not start any arguments, not implicitly having someone being called an idiot and not be upsetting in any way.

Clearly I was wrong.
  • #10
  • Nov 10, 2013 8:58am Nov 10, 2013 8:58am
Quoting AimHigher
and true to general form here on FF and other forums, the first reply assumed the thread starter is an idiot
This is a public forum. Assuming that other people are retarded is the safest bet anyone can ever make, and it will and does pay dividends more than it'll ever lose you.

Quote
I was simply going to use if for some rudimentary testing and wanted to save development time

But what is it that you are even asking? You mention AND and OR, not just typical math, so are you wanting something that can interpret mql, or some other language, from within mql or a dll? MAYBE you might find a generic calculator module you can put in a dll and import, or rewrite in mql, but if you are after some type of interpreter then asking here is the last place you'll find anything. You didn't even specify what language you are trying to interpret.

Either you don't know exactly what it is you want, are wanting something that is unreasonable to want, or somewhere somehow the message you are sending has been misunderstood by at least 2 people so far.
Congratulations ScalaFX for coming out of the closet!
  • #11
  • Nov 10, 2013 9:31am Nov 10, 2013 9:31am
Quoting AimHigher
Wow, 7 replies without me even participating and true to general form here on FF and other forums, the first reply assumed the thread starter is an idiot. Since Eval/Evaluate exists in several other programming languages (http://en.wikipedia.org/wiki/Eval), I though it was conceivable that someone had created/knew about a dll file that included the Eval function (e.g. by calling VBScript that has that function built it) and that such a dll could be accessed using #import in mql4. I very well know that Eval isn't necessary (you can work...
if you look at it again, you will see that I didn't call you an idiot and in fact, I said in my second post that I had missed the essence of your request so yes clearly you are wrong....

equally as you are so knowledgeable you already know the answer that mql is not the strongest programming language as it is designed for trading and that what you seek is far better done outside of metatrader anyway.... enjoy your stay
  • #12
  • Nov 10, 2013 9:33am Nov 10, 2013 9:33am
nubcake,

I personally don't get any gratification at all from putting other people down, even if they do indeed show a complete lack of understanding even their own question. Either I respond reasonably politely or I don't respond at all. That is just the person I want to be. Others can do as they wish. Quite frequently however it is the person who gives the smarta$$ reply that has misunderstood the question. Case in point. I do however appreciate that you have entertained my question in a perfectly polite and professional manner.

Obviously I wasn't detailed enough in my initial question and quite possibly my question was unreasonable, especially since c\c++ doesn't have that function. It also became clear that I only needed a very specific subset of the Eval functionality, so I just wrote that as a mql4 function instead. Thanks for your time.
  • #13
  • Nov 10, 2013 9:49am Nov 10, 2013 9:49am
MaxDoom,

Your first answer did IMO imply I knew virtually nothing and was asking a "stupid" question i.e being an idiot. The fact that is was a result of you misunderstanding my question didn't help. I see it so often that I am pretty annoyed about it. You did however correct yourself and that is pretty rare so kudos to you.

I am definitely not particularly knowledgeable about programming, certainly not compared to you, nubcake, 7bit et al, so that is why I asked the question in the first place. Your answers were indeed helpful since they made it clear to me that I should most likely find an alternative solution, which I did. So thanks for sending me in the right direction.
  • #14
  • Last Post: Nov 10, 2013 9:59am Nov 10, 2013 9:59am
Quoting AimHigher
MaxDoom, Your first answer did IMO imply I knew virtually nothing and was asking a "stupid" question i.e being an idiot. The fact that is was a result of you misunderstanding my question didn't help. I see it so often that I am pretty annoyed about it. You did however correct yourself and that is pretty rare so kudos to you. I am definitely not particularly knowledgeable about programming, certainly not compared to you, nubcake, 7bit et al, so that is why I asked the question in the first place. Your answers were indeed helpful since they made it...
well no point getting annoyed it won't change anything, glad that you have found a path
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