feat: expose lambda and higher-order array functions#1561
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Add a Pythonic API for DataFusion's higher-order array functions and the lambda expressions they consume. - Rust: lambda_, lambda_var, array_transform, and array_any_match pyfunctions, plus a ResolveLambdaVariables analyzer rule so expression-builder plans (which emit unresolved lambda variables) resolve before optimization. - Python: array_transform / array_any_match (with list_transform, any_match, list_any_match aliases) accept either a Python callable or an explicit lambda built with lambda_ / lambda_var. Callables are introspected so their parameter names become the lambda parameters. - Tests and docs (expressions guide + agent skill), noting v1 limits: lambda expressions are not serializable, and SQL arrow syntax needs the DuckDB dialect.
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Which issue does this PR close?
Closes #811
Rationale for this change
DataFusion gained lambda expressions and higher-order array functions (apache/datafusion#21172). The Python binding already had the read-only
Lambda,HigherOrderFunction, andLambdaVariablewrapper classes, but offered no way to construct a lambda or call the higher-order functions. This PR adds a Pythonic API for both.What changes are included in this PR?
Adds the following:
array_transformandarray_any_matchthat accept either a Python callable or an explicit lambda built withlambda_/lambda_varAre there any user-facing changes?
There are new APIs but they are all new additions.