I think think is doable. I'll take a look. Thanks, Chinmay.
On Thu, Jan 14, 2016 at 1:59 PM, Timothy Farkas <[email protected]> wrote: > Haven't gone though you're PR, so I'm not sure how this would fit in. But I > think introducing an interface like below, and allowing it to be set may be > sufficient. > > public interface ExpressionParser > { > public String convertToJavaExpression(String expression); > } > > Thanks, > Tim > > On Thu, Jan 14, 2016 at 12:19 AM, Chinmay Kolhatkar < > [email protected] > > wrote: > > > Ah got it. That's a good point. Maybe its good to separate the parsing > and > > compilation part of the evaluation. > > And let one override the parsing logic. > > > > I'll see how to incorporate that, but if you have idea about achieving > it, > > please share it. > > > > Thanks, > > Chinmay. > > > > > > On Thu, Jan 14, 2016 at 1:43 PM, Timothy Farkas <[email protected]> > > wrote: > > > > > Hey Chinmay, > > > > > > It is possible the user may want to define a syntax radically different > > > from Java style syntax. I've proposed a syntax similar to yours to one > of > > > our users for expression evaluation but they didn't like it because the > > > syntax needs to be something easily validated by a UI. It may be > possible > > > that the user wants expressions to be sent to an operator as json, > > because > > > that is easy to parse and validate in javascript: > > > > > > {"param":"myField1","operation":">","threshold":"1"} > > > > > > If the syntax is pluggable then an implementation of this syntax could > be > > > swapped with with an implementation of the syntax you've already > provided > > > without changing operator code. > > > > > > Thanks, > > > Tim > > > > > > On Wed, Jan 13, 2016 at 11:34 PM, Chinmay Kolhatkar < > > > [email protected] > > > > wrote: > > > > > > > Hi tim, > > > > > > > > I agree with you. The expression here we're talking about is really a > > > > quasi-Java expression. One can do anything which java does. > > > > Only change with java syntax here is how variables are accessed. > > > > > > > > They're by default accessed as ${...}. > > > > > > > > But this is also made configurable via a setter property on > > > > ExpressionEvaluator. The pull request has it. > > > > > > > > If this is what you're talking about then this is taken care of. > > > > > > > > Thanks, > > > > Chinmay. > > > > > > > > > > > > On Thu, Jan 14, 2016 at 1:00 PM, Timothy Farkas <[email protected] > > > > > > wrote: > > > > > > > > > Hi Chinmay, > > > > > > > > > > I think this is a very good first implementation. My only concern > is > > > that > > > > > people will get caught up in the details of the syntax for this > > > > expression > > > > > language. I think a way to avoid that is to make the syntax > > pluggable. > > > > For > > > > > example is there an interface for expression evaluation which can > be > > > > > implemented by different syntaxes? This would allow operators which > > use > > > > > expression evaluation to have the syntax configured via a property. > > > That > > > > > way if someone discovers a limitation in the syntax down the line, > a > > > new > > > > > syntax can be introduced without breaking backwards compatibility > and > > > > > without requiring operator code to be changed. > > > > > > > > > > Thanks, > > > > > Tim > > > > > > > > > > On Wed, Jan 13, 2016 at 10:52 PM, Chinmay Kolhatkar < > > > > > [email protected] > > > > > > wrote: > > > > > > > > > > > Hi All, > > > > > > > > > > > > I'm working on APEXCORE-1972 which adds support for a quasi-Java > > > > > Expression > > > > > > Language and its expression evaluator. > > > > > > > > > > > > All the detailed functionality and design details along with > > examples > > > > are > > > > > > present in Jira. > > > > > > > > > > > > I've summarized the ExpressionEvaluator feature & Expression > > language > > > > > > below. > > > > > > > > > > > > The pull request created for this at here: > > > > > > https://github.com/apache/incubator-apex-malhar/pull/170 > > > > > > > > > > > > Please share your thought on this. > > > > > > > > > > > > Thanks, > > > > > > Chinmay. > > > > > > > > > > > > > > > > > > *Summary of functionality of ExpressionEvaluator:* > > > > > > > > > > > > 1. Support quasi-Java Expression which defines a single line > > > > > executable > > > > > > expression > > > > > > 2. Support for quasi-Java expression based function code, > which > > > will > > > > > be > > > > > > compiled on the fly and made available for execution. > > > > > > 3. Should support accessing multiple fields from multiples > input > > > > POJOs > > > > > > while addressing the conversion of private variables to public > > > > getter > > > > > > method for all levels. > > > > > > 4. Should support nested field support > > > > > > 5. quasi-Java expressions should support operands to be > > mentioned > > > in > > > > > > following ways: > > > > > > - ${input.fieldName} > > > > > > - Access fieldName via a object name. > > > > > > - ${fieldName} > > > > > > - Accessing fieldName directly when a single object is > > > > > registered > > > > > > for operation. > > > > > > - ${input} > > > > > > - Accessing object variable directly > > > > > > - ${input.fieldName.internalField} > > > > > > - Accessing nested fields > > > > > > 6. There should be some predefined function provided to > > > > expression > > > > > > writer which one can directly use in expression for invoking > > > certain > > > > > > functionality. > > > > > > 7. These are simple String based, Date time based etc > functions. > > > > > > 8. On-need-basic one should be able to easily update > Expression > > > > > > Evaluator to easily add new predefined functions to be made > > > > available > > > > > > for > > > > > > expression writer. > > > > > > 9. User of ExpressionEvaluator should be able to add a custom > > > method > > > > > > externally to be made available to in expression. > > > > > > 10. Though operands are defined, placeholder for the operand > in > > > > > > expression should be allowed to be overridden. By default, > > > > expression > > > > > > language should support bash type syntax for operand - {…} > > > > > > 11. The library should not introduce any serialization related > > > > issues. > > > > > > 12. All the java operators should be supported. > > > > > > > > > > > > > > > > > > > > > > > > *The examples of quasi-Java Expression:* > > > > > > > > > > > > - ${inp.field1} > > > > > > - Will return value of field1 from registered input POJO. > > > > > > - ${inp.field1} + ${inp.field2} > > > > > > - Will return sum of field1 & field2 from given POJO > > > > > > - ${field1} + ${field2} > > > > > > - Equivalent to above > > > > > > - ${inpA.field1} > ${inpA.field2} ? ${inpA.field3} : > > > ${inpB.field3} > > > > > > - Executes ternary expression and returns value > accordingly. > > > > Works > > > > > on > > > > > > 2 POJOs. inpA & inpB are two placeholder registered for > given > > > > POJO > > > > > > with > > > > > > ExpressionEvaluator library. > > > > > > - pow(${inpA.field1}, ${inpB.field2}) > > > > > > - Executes pow function coming from java.lang.Math library. > > > This > > > > > and > > > > > > other with lot other basic functions is available to > > expression > > > > > > writer out > > > > > > of the box to use in expression. > > > > > > - ${inpA.field1} > 0 ? ${inpB.innerPOJO.field3} : > > > > > > ${inpA.innerPOJO.field3} > > > > > > - Shows how nested POJOs can be accessed in expression. The > > > > > variables > > > > > > will evaluate to correct public getter method is required. > > > > > > - ${inp.firstname} + “ “ + ${inp.lastname} > > > > > > - Generate the full name as per given expression from > > firstname > > > > and > > > > > > lastname field. > > > > > > - long retVal=1; for (int i=0; ${inpF.value1}; i++) {retVal = > > > > retVal * > > > > > > ${inpF.value1}; } return retVal; > > > > > > - This tells a complete method content to > > ExpressionEvaluator. > > > > The > > > > > > library create an executable and compiled method using this > > > > > > expression. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
