Comments (3)
According to the README there's no way to specify operator precedence:
Operator precedence follows standard BODMAS order, with multiplication/division given precedence over addition/subtraction. Prefix operators take precedence over postfix operators, which take precedence over infix ones. There is currently no way to specify precedence for custom operators - they all have equal priority to addition/subtraction.
My understanding is that if you use that input/pure constructor and return nil
, it should fallback to the built-in operators. Do you have an example where your code doesn't work as expected?
(Note that it should be fine to define your ^
operator as a pure symbol, as what it returns is always the same for the same input arguments.)
from expression.
@ajkendall what @nighthawk said is correct. There is not currently any way to define precedence in the API. There is a hard-coded precedence table for common operators defined in the library, but any that are not defined (including ^) will have a precedence of zero (the same as +) by default.
I'm not sure off the top of my head if that's an appropriate default for ^. I guess that maybe it should have the same precedence as * instead? In which case feel free to add it to the internal precedence table and make a PR.
FWIW the reason I don't define ^ as one of the standard operators is that it is used to mean pow() in some languages and xor in others (with ** being the pow operator), so there didn't seem to be a clear choice as to which should be the default.
from expression.
@nighthawk thanks for pointing out that line in the ReadMe - I definitely missed that bit.... @nicklockwood - I hadn't considered the xor interpretation. Thanks a bunch for pointing out the precedence table. Making a PR seems like the best solution.
from expression.
Related Issues (20)
- Question: Overloading existing operators HOT 2
- Usage for macOS Apps (Swift 5.1/Xcode 11.2.1) HOT 3
- Equality of strings, substrings and characters HOT 1
- Square brackets HOT 1
- when using the sample code it won't execute HOT 4
- Expression.parse("'\\n'") fails HOT 2
- AnyExpression using array variables can't be evaluated with error 0 HOT 1
- Expose AST HOT 1
- Test suite crashes on Xcode 13.3 / Swift 5.6 HOT 7
- Ability to use ^ instead of pow(x, y) HOT 4
- Question: Can multiplication be done with parentheses? HOT 1
- Function expression failed with string paramater which contains \ HOT 1
- Crash in Swift 5.7 when creating stringBounds error HOT 4
- Getting sub expressions during evaluation HOT 1
- Lazy evaluation of ternary operator's true/false cases HOT 1
- Question: Is implicit multiplication possible with Expression? HOT 5
- Support ^ as pow operator HOT 2
- Fact `!` postfix operator does not work HOT 6
- Complex expressions are not working HOT 6
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from expression.