Hylograph.Expr.Datum

class DatumExpr :: (Type -> Type) -> Row Type -> Constraintclass DatumExpr (repr :: Type -> Type) (datumRow :: Row Type) | repr -> datumRow where

Datum field access with compile-time safety

The datumRow parameter is a Row kind (not Type), representing the fields available in the datum record. The constraint Row.Cons sym a r datumRow ensures:

• datumRow contains a field named sym
• The field has type a
• Compiler error if field doesn't exist

The interpreter works with Record datumRow at runtime.

Members

• field :: forall a sym r. IsSymbol sym => Cons sym a r datumRow => Proxy sym -> repr a

  Access a field from the datum

  -- With wrapper functions (recommended):
  x :: forall repr. DatumExpr repr (x :: Number, y :: Number) => repr Number
  x = field (Proxy :: Proxy "x")
  
  -- Or with visible type applications:
  field @"x" :: repr Number
  

• index :: repr Int

  Access the element index (for indexed operations)