gstvg commented on code in PR #18921:
URL: https://github.com/apache/datafusion/pull/18921#discussion_r3005982227
##########
datafusion/expr/src/expr.rs:
##########
@@ -404,6 +406,104 @@ pub enum Expr {
OuterReferenceColumn(FieldRef, Column),
/// Unnest expression
Unnest(Unnest),
+ /// Call a lambda function with a set of arguments.
+ ///
+ /// For example, `array_transform([1,2,3], v -> v+1)` would be equivalent
to:
+ ///
+ /// ```text
+ /// LambdaFunction(array_transform)
+ /// ├── args[0]: Literal([1,2,3])
+ /// └── args[1]: Lambda
+ /// ├── params: ["v"]
+ /// └── body: BinaryExpr(+)
+ /// ├── LambdaVariable("v")
+ /// └── Literal(1)
+ /// ```
+ LambdaFunction(LambdaFunction),
Review Comment:
Hmm, definitely should be higher-order function, yes
https://github.com/apache/datafusion/pull/18921/changes/66839d3a76c8b6a3029c97b7472e2534ce543bd3,
thank you. Other symbols got renamed as well like `LambdaUDF` to
`HigherOrderUDF`, `LambdaSignature` to `HigherOrderSignature`, etc
For now it supports only anonymous inline functions, yes, but we can add
support for it too. Maybe with a
[FunctionRewrite](https://docs.rs/datafusion/latest/datafusion/logical_expr/expr_rewriter/trait.FunctionRewrite.html)
that rewrites the scalar UDF name into an anonynomous inline function? (I
believe it can be done out-of-tree as well)
I imagine that trying to natively support names would hide the scalar udf
call from tree traversals that may be necessary, like type coercion, and also
somehow require the function instance access to the specific scalar udf it got
called, like reinstancing the function with the udf, or providing the scalar
functions map to `HigherOrderFunction` methods `invoke_with_args` and
`return_field_from_args`, which wouldn't be as trivial as the `FunctionRewrite`
approach
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