pure dome
My program is taking in strings such as "5.5 + 5", "sin(90)", "5^2" and so fourth. How can I categorise pieces of the string? (5 is a number and + is an operation etc) And how can I process the pieces so I can return 10.5 after "5.5 + 5"?
Here is the list of valid pieces I want in my program.
nums, decimal and negator:
1 2 3 4 5 6 7 8 9 0 . -
operations:
+ - * / ^
math commands:
sin(...) cos(...) tan(...) sqrt(...)
custom commands:
help quit
native quartzBOT
hollow surge
the step of taking a string and splitting it up into individual tokens (pieces) is called tokenization
from those tokens you can create an abstract sytax tree you do that with a parser constructs that AST based on a grammar
once you have an AST you can evaluate it
pure dome
thanks! I'll look it up
pure dome
haha I'll try to keep it simple then 😅
hollow surge
it took me the better part of a year to understand parsing and being able to write my own grammar
if you dont want to write your own parser take a look at
there are tons of parser generators
oh and
pure dome
feels a bit cheaty since this is the hardest part of the program. do you think it is too hard for a beginner using the tokens listed above as well as () and spaces for separation?
hardy parrot
When I made my own calculator app I consumed tokens and then immediately evaluated them.
pure dome
haha very well, I'll keep this thread open and look at different articles for now
subtle raptor
feels a bit cheaty since this is the hardest part of the program. do you think i...
Don't worry, you will better understand what you want from a parser
hollow surge
yeah theres also a thing called uh
hardy parrot
When I made my own calculator app I consumed tokens and then immediately evaluat...
It still works: https://leduyquang753.github.io/calcit/
hollow surge
thats straight forward
you convert smth like
1 + 2 (infix notation)
into
hardy parrot
You don't need the "to Polish notation" part if all you want is to build a syntax tree or to evaluate it.
subtle raptor
It still works: https://leduyquang753.github.io/calcit/
how to take sqrt? it's throwing an error
hardy parrot
It's 2#value.
subtle raptor
ok
hollow surge
You don't need the "to Polish notation" part if all you want is to build a synta...
sure, there are many ways to accomplish the same goal
night berry
My program is taking in strings such as "5.5 + 5", "sin(90)", "5^2" and so fourt...
Shunting Yard is one algorithm that takes infix expressions such as those you mentioned above and turns them into rpn or postfix notation which is then easier to evaluate.
You can process the string itself through shunting yard but it's better if you tokenize it first (lexer)
native quartzBOT
@pure dome Has your question been resolved? If so, type !solved :)
desert lily
@pure dome I highly recommend reading this Parsing Expressions chapter from the free book Crafting Interpreters, which explains how Recursive Descent can be used to parse any expression:
https://craftinginterpreters.com/parsing-expressions.html
pure dome
thanks everyone, haven't progressed a lot but working on a tokenizer. if anyone is interested, I found a very good video about the shunting yard algorithm
native quartzBOT
@pure dome Has your question been resolved? If so, type !solved :)
tribal cove
feels a bit cheaty since this is the hardest part of the program. do you think i...
I would recommend not to use a parser library/framework thingy, and stick to libc/basic stuff. Making an expression parser like this is not insanely difficult, and is a very good exercise in data hierarchies. I’ve done it before (in another language) using only stacks to handle the program data.
