rpn: remove exported Number type alias

type Number = NumericValue was a legacy alias that created confusion
— callers could use Number or NumericValue interchangeably. Removed
the alias and updated:
- NewNumber/NewNumberWithMetric return types: Number -> NumericValue
- Comments referencing Number now say NumericValue

The alias added no value since Number was never used as a distinct
type anywhere in the codebase.

4 files changed, 12 insertions, 9 deletions

diff --git a/internal/rpn/number.go b/internal/rpn/number.go
index a188edf..de6fa93 100644
--- a/internal/rpn/number.go
+++ b/internal/rpn/number.go
@@ -44,8 +44,11 @@ type NumericValue interface {
 	SetMetric(m *Metric) NumericValue
 }
 
-// Number is the legacy alias for NumericValue, kept for backward compatibility.
-type Number = NumericValue
+// NumericValue is the interface for numeric values (float64 or *big.Rat).
+// It extends StackValue with metric operations.
+//
+// Note: type Number was a legacy alias for NumericValue, removed to avoid
+// confusion between the alias and the concrete type.
 
 // Compile-time interface satisfaction checks.
 var _ StackValue = (*Float)(nil)
@@ -55,20 +58,20 @@ var _ NumericValue = (*Rat)(nil)
 var _ StackValue = (*StringNum)(nil)
 var _ StackValue = (*Symbol)(nil)
 
-// NewNumber creates a Number from a float64 value with the given mode.
+// NewNumber creates a NumericValue from a float64 value with the given mode.
 // The actual type depends on the current calculation mode (Float or Rat).
 // The metric defaults to Cool (unitless).
-func NewNumber(value float64, mode CalculationMode) Number {
+func NewNumber(value float64, mode CalculationMode) NumericValue {
 	if mode == RationalMode {
 		return NewRat(value)
 	}
 	return NewFloat(value)
 }
 
-// NewNumberWithMetric creates a Number from a float64 value with an explicit metric.
+// NewNumberWithMetric creates a NumericValue from a float64 value with an explicit metric.
 // The actual type depends on the current calculation mode (Float or Rat).
 // If metric is nil, defaults to Cool.
-func NewNumberWithMetric(value float64, mode CalculationMode, metric *Metric) Number {
+func NewNumberWithMetric(value float64, mode CalculationMode, metric *Metric) NumericValue {
 	if metric == nil {
 		metric = GetCoolMetric()
 	}
diff --git a/internal/rpn/operations_constants.go b/internal/rpn/operations_constants.go
index 7fbd4c9..8cb0366 100644
--- a/internal/rpn/operations_constants.go
+++ b/internal/rpn/operations_constants.go
@@ -19,7 +19,7 @@ func (o *Operations) ListConstants() (string, error) {
 		}
 		sb.WriteString(info.Name)
 		sb.WriteString(" = ")
-		// Use Number interface for consistent formatting
+		// Use NumericValue interface for consistent formatting
 		num := NewNumber(info.Value, FloatMode)
 		sb.WriteString(num.String())
 	}
diff --git a/internal/rpn/operations_variables.go b/internal/rpn/operations_variables.go
index fb340ec..49cab57 100644
--- a/internal/rpn/operations_variables.go
+++ b/internal/rpn/operations_variables.go
@@ -25,7 +25,7 @@ func (o *Operations) AssignVariable(stack *Stack, name string) error {
 		return err
 	}
 
-	// Convert Number to float64 for variable storage
+	// Convert NumericValue to float64 for variable storage
 	valF, err := toFloat64(val, "assigning variable")
 	if err != nil {
 		return err
diff --git a/internal/rpn/variables.go b/internal/rpn/variables.go
index 56eb1ae..ac04cf1 100644
--- a/internal/rpn/variables.go
+++ b/internal/rpn/variables.go
@@ -185,7 +185,7 @@ func (v *Variables) formatVariablesUnsafe() string {
 		if i > 0 {
 			sb.WriteString("\n")
 		}
-		// Use Number interface for consistent formatting
+		// Use NumericValue interface for consistent formatting
 		num := NewNumber(info.Value, FloatMode)
 		sb.WriteString(info.Name)
 		sb.WriteString(" = ")