Support for expression

[goxiaoy]

The surveyjs javascript use pegjs to parse expression, and use condition runner to provide logic features

• triggers
  • runexpression
• calculatedValues
• question logic
  • visibleIf
  • enableIf
  • defaultValueExpression
  • choicesVisibleIf
  • choicesEnableIf
• question type
  • expression

original codes : https://github.com/surveyjs/survey-library/tree/master/src/expressions https://github.com/surveyjs/survey-library/blob/master/src/conditions.ts https://github.com/surveyjs/survey-library/blob/master/src/conditionsParser.ts https://github.com/surveyjs/survey-library/blob/master/src/conditionProcessValue.ts

Paths to achieve this	Index	Path	Desc	Implement difficulty	Maintain difficulty
1	Fully rewrite with dart	💪	⭐⭐⭐⭐⭐	⭐⭐⭐⭐⭐
2	Use js engine in dart	Build tools to convert original js codes to single file. and run as js in dart	⭐⭐⭐⭐	⭐⭐
3	Rewrite with antlr4	rewrite expression parser with antlr4,	⭐⭐⭐⭐	⭐⭐⭐
4	Use WebAssembly (WASM)	compile js into WASM and embed it into Flutter	Unknown	Unknown

[laogao]

Is it possible to take advantage of existing dart parsers out there such as https://pub.dev/packages/expressions or something more fundamental like https://pub.dev/packages/petitparser ?

[goxiaoy]

@laogao Thanks for your reference. We need more time to investigate those packages, and they might help us to reduce the implementation and maintainance difficulty of path 1

[ChopinDavid]

I've researched PEG a bit. petitparser came up during my research. From my investigation, there didn't seem to be many good dart PEG parsers. But finding one would make implementing conditions pretty seamless.

[goxiaoy]

implemented with js engine. would close via 3b6eb9a8274a16876dfcdac3ad6e4254f20b97ee