BASIC Parser

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Summary:

Write a program that parses a mathematical expression, like expr(, without using expr(.

Math Parser

Edward H 18 Jun 2008 22:06

Edit: okay, I've since decided that the original challenge was perhaps too ambitious a goal for BASIC. I've modified it, slightly.

Using pure TI-BASIC, write the smallest program that parses a mathematical expression stored in Str0, without using expr( or storing strings to functions or tricky things like that. The program needs to handle addition, subtraction, multiplication, division, exponentiation, unary negation, factorials, and parentheses with proper operator precedence and the proper direction for associativity.

Hint.

Last edited on 19 Jun 2008 19:32 by Edward H Show more

Re: Math Parser

builderboy 18 Jun 2008 22:36

hmmm, thats going to be tricky…

i'l get back to you on that…

Re: Math Parser

builderboy 19 Jun 2008 15:55

Alright, i got it!

Input A
Disp A

Just type you equation directly into the prompt!

Re: Math Parser

Edward H 19 Jun 2008 19:28

See, that would qualify under "tricky things like that." Try again ;).

Re: Math Parser

Zaphod Beeblebrox 20 Jun 2008 02:14

Something like this would require expr( to just interpret individual numbers. Otherwise you'd have to write a separate engine just to parse a single number and account for negatives and decimals which would be very possible, but time consuming and useless.

Re: Math Parser

Edward H 20 Jun 2008 02:42

I'm not sure how many bytes this is, but it was definitely not time consuming, and is definitely not useless, because I use code like this in my chemical equation balancer to interpret the coefficients efficiently.

Delvar X
inString(Str1+".",".→A
For(I,1,length(Str1
inString("0123456789",sub(Str1,X,1
If Ans
X+(Ans-1)10^(A-I-(A>I→X
End
X(1-2(sub(Str1,1,1)="-

Last edited on 20 Jun 2008 02:43 by Edward H Show more

Re: Math Parser

RandomProductions 30 Jun 2008 17:06

I call it the Do It Yourself Parser!

:Input "EQUATION?", Str0
:Disp "NOW YOU HAVE TO", "PARSE IT (TYPE", "IT AGAIN)"
:Input "EQUATION?", A
:Disp A

Well, you do put the equation in Str0, and then the equation gets "parsed"…by the user! :P

Re: BASIC Parser

builderboy 30 Jun 2008 16:24

Input Str1
Str1→u
Disp u

:D

Re: BASIC Parser

burr 30 Jun 2008 19:13

What's the reason for using a graphing equation variable?

Re: BASIC Parser

builderboy 30 Jun 2008 19:32

u has the unique property to store strings in number format and are automatically parsed when accessed. Just a way around using exp(

(although, u is different in that if you store "Ans+2" to u, and then access u, it will calculate Ans+2)

Re: BASIC Parser

burr 30 Jun 2008 20:31

That's creative thinking :D

Re: BASIC Parser

Edward H 01 Jul 2008 04:51

Oh, quit that, builderboy!

without using expr( or storing strings to functions or tricky things like that.

Note: you could also store to Y₁, or any other function, I believe. If you just type "Y₁" without the "(X" part, the calc just parses the function without changing X.

Last edited on 01 Jul 2008 04:55 by Edward H Show more

Re: BASIC Parser

builderboy 01 Jul 2008 05:02

I'm just pointing out that there are numerous ways to do this already built into the calculator, so its rather pointless to write a program that does it, because the program will almost never be as good or as complete as the pre-built one.

Re: BASIC Parser

theUnnamed 27 Apr 2010 14:12

Unless you need access to the syntax tree =) although even then I would use expr to interpret numbers

Re: BASIC Parser

builderboy 27 Apr 2010 16:08

A little old thread, but on a side note, I did actually eventually go on to write a Basic equation parser. It supports addition, subtraction, multiplication, division, exponentiating, and parentheses. It does use Expr() to extract the numbers from the string tho, to keep the speed while still maintaining the original idea. I could write a string to number program though :P

I also had to write a number string program that would be faster than the LinearRegression trick, and that was a pain.

Re: BASIC Parser

theUnnamed 27 Apr 2010 23:00

could I have the code to that? it could aid me in my symbolic math endeavors.