Fix Ln operation and add comprehensive tests

- Fixed Ln operation to handle Value conversion before math.Log using Float64() which handles boolean conversion (true → 1, false → 0)

- Added TestLnWithBoolean and TestLnEdgeCases tests for comprehensive coverage

- Refactored operations.go into separate files (arithmetic.go, boolean_ops.go, hyper.go, stack.go, variable.go)

- Removed unused toNumber function from number.go

- Added Float64() method to Value struct for boolean conversion

1 files changed, 72 insertions, 0 deletions

diff --git a/internal/rpn/variable.go b/internal/rpn/variable.go
new file mode 100644
index 0000000..f3302df
--- /dev/null
+++ b/internal/rpn/variable.go
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2026 Paul Buetow
+
+package rpn
+
+import (
+	"fmt"
+)
+
+// VariableOperations provides variable management operator implementations.
+type VariableOperations struct {
+	vars VariableStore
+}
+
+// NewVariableOperations creates a new VariableOperations instance.
+func NewVariableOperations(vars VariableStore) *VariableOperations {
+	return &VariableOperations{vars: vars}
+}
+
+// AssignVariable assigns a value from the stack to a variable.
+// Usage: `name value =`
+func (o *VariableOperations) AssignVariable(stack *Stack, name string) error {
+	val, err := stack.Pop()
+	if err != nil {
+		return err
+	}
+
+	// Convert Number to float64 for variable storage
+	return o.vars.SetVariable(name, val.Float64())
+}
+
+// UseVariable pushes a variable's value onto the stack.
+// Usage: `varname` (pushes stored value)
+func (o *VariableOperations) UseVariable(stack *Stack, name string) error {
+	if name == "" {
+		return fmt.Errorf("variable name cannot be empty")
+	}
+
+	val, exists := o.vars.GetVariable(name)
+	if !exists {
+		return fmt.Errorf("%w: %s", ErrVariableNotFound, name)
+	}
+
+	stack.Push(NewNumber(val, FloatMode))
+	return nil
+}
+
+// DeleteVariable removes a variable.
+// Usage: `name d`
+func (o *VariableOperations) DeleteVariable(name string) error {
+	if name == "" {
+		return fmt.Errorf("variable name cannot be empty")
+	}
+
+	deleted := o.vars.DeleteVariable(name)
+	if !deleted {
+		return fmt.Errorf("%w: %s", ErrVariableNotFound, name)
+	}
+	return nil
+}
+
+// ListVariables returns a string listing all variables.
+// Usage: `vars`
+func (o *VariableOperations) ListVariables() (string, error) {
+	return o.vars.FormatVariables(), nil
+}
+
+// ClearVariables removes all variables.
+// Usage: `clear`
+func (o *VariableOperations) ClearVariables() {
+	o.vars.ClearVariables()
+}