Variable argument Generic functions & fixes

kamimark commented 3 years ago

Added capability to create generic functions with variable arguments like min, max,. Fixed issue when passing negative value to a function as not the first argument. Ex. min(0,-2)

fkleon commented 3 years ago

Thanks for this pull request, @kamimark. It's a great feature. I'll have a closer look later this week.

fkleon commented 3 years ago

Sorry for the delay in getting back to you about this.

I've reviewed these changes and was missing some tests to satisfy myself that it's working as intended. So I've gone ahead and added some tests and usage example to this on the generic-functions branch. Have a look at those and let me know what you think. The example is essentially this:

Parser p = Parser();
p.addGenericFunction('my_min', (List<double> args) => args.reduce(math.min));
Expression exp = p.parse('my_min(1, x, -1)');

With those changes, this library would have two ways to define "custom" functions:

CustomFunction: This is a formal mathematical function definition that allows to bind a function to an Expression. It only takes variables as arguments. No parser support.
GenericFunction: This is a bridge interface to pass values for evaluation to Dart code. It takes arbitrary expressions as arguments. There's parser support.
However this function isn't well specified in mathematical terms, so we can't perform expression validation, or support any of the built-in features like simplification/differentiation. I think this is important information and needs to be added to the documentation of the class.

The naming doesn't make this important distinction very clear, but I also don't have a better suggestion right now.

Let me know what you think, still happy to merge this (with tests from my branch).

kamimark commented 3 years ago

Seems good. I guess the name can be AlgorithmicFunction instead of generic

About the double type, maybe it can just throw exception? Since it doesn't make much sense not to return double? Maybe it does... Not sure.

On Sat, Jul 31, 2021, 14:20 Frederik Leonhardt @.***> wrote:

@.**** commented on this pull request.

In lib/src/functions.dart https://github.com/fkleon/math-expressions/pull/54#discussion_r680346684 :

@@ -943,3 +950,24 @@ class Sgn extends DefaultFunction { throw UnimplementedError('Can not evaluate $name on $type yet.'); } } + +class GenericFunction extends DefaultFunction {

/// Creates a genetic function with variable number of arguments.

///

/// For example, to create min(2,23,4,5,2314,213,5,324):

///

GenericFunction(String name, List args, this.handler) : super._any(name, args);

dynamic handler;

@override

dynamic evaluate(EvaluationType type, ContextModel context) {

List values = args.map((v) => (v.value ?? context.getExpression(v.name)).evaluate(type, context)).toList();

This mapping needs to go into the if (type == EvaluationType.REAL) block below since we can't guarantee that evaluate on each expression will always result in a double.

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fkleon commented 3 years ago

Thank you again, have published this as version 2.2.0

fkleon / math-expressions

Variable argument Generic functions & fixes #54

@.**** commented on this pull request.