Package io.substrait.expression

Class LambdaBuilder

java.lang.Object
io.substrait.expression.LambdaBuilder
public class LambdaBuilder extends Object
Builds lambda expressions with build-time validation of parameter references.

Maintains a stack of lambda parameter scopes. Each call to lambda(java.util.List<io.substrait.type.Type>, java.util.function.Function<io.substrait.expression.LambdaBuilder.Scope, io.substrait.expression.Expression>) pushes parameters onto the stack, builds the body via a callback, and pops. Nested lambdas simply call lambda() again on the same builder.

The callback receives a LambdaBuilder.Scope handle for creating validated parameter references. The correct stepsOut value is computed automatically from the stack. 


 LambdaBuilder lb = new LambdaBuilder();

 // Simple: (x: i32) -> x
 Expression.Lambda simple = lb.lambda(List.of(R.I32), params -> params.ref(0));

 // Nested: (x: i32) -> (y: i64) -> add(x, y)
 Expression.Lambda nested = lb.lambda(List.of(R.I32), outer ->
     lb.lambda(List.of(R.I64), inner ->
         add(outer.ref(0), inner.ref(0))
     )
 );

  • Constructor Details

    • LambdaBuilder

      public LambdaBuilder()

  • Method Details

    • lambda

      public Expression.Lambda lambda(List<Type> paramTypes, Function<LambdaBuilder.Scope,Expression> bodyFn)
      Builds a lambda expression. The body function receives a LambdaBuilder.Scope for creating validated parameter references. Nested lambdas are built by calling this method again inside the callback.
      Parameters:
      paramTypes - the lambda's parameter types
      bodyFn - function that builds the lambda body given a scope handle
      Returns:
      the constructed lambda expression

    • lambdaFromStruct

      public Expression.Lambda lambdaFromStruct(Type.Struct params, Supplier<Expression> bodyFn)
      Builds a lambda expression from a pre-built parameter struct. Used by internal converters that already have a Type.Struct (e.g., during protobuf deserialization).
      Parameters:
      params - the lambda's parameter struct
      bodyFn - function that builds the lambda body
      Returns:
      the constructed lambda expression

    • resolveParams

      public Type.Struct resolveParams(int stepsOut)
      Resolves the parameter struct for a lambda at the given stepsOut from the current innermost scope. Used by internal converters to validate lambda parameter references during deserialization.
      Parameters:
      stepsOut - number of lambda scopes to traverse outward (0 = current/innermost)
      Returns:
      the parameter struct at the target scope level
      Throws:
      IllegalArgumentException - if stepsOut exceeds the current nesting depth

    • newParameterReference

      public FieldReference newParameterReference(int stepsOut, int paramIndex)
      Creates a validated field reference to a lambda parameter. Validates that stepsOut is valid for the current lambda nesting context.
      Parameters:
      stepsOut - number of lambda scopes to traverse outward (0 = current/innermost)
      paramIndex - index of the parameter within the target lambda's parameter struct
      Returns:
      a field reference to the specified lambda parameter
      Throws:
      IllegalArgumentException - if stepsOut exceeds the current nesting depth
      IndexOutOfBoundsException - if paramIndex is out of bounds for the target lambda