2 files changed, 34 insertions, 4 deletions
diff --git a/internal/rpn/number.go b/internal/rpn/number.go
index bb6f765..2915a2a 100644
--- a/internal/rpn/number.go
+++ b/internal/rpn/number.go
@@ -186,7 +186,8 @@ func (f *Float) Mod(other Number) (Number, error) {
 // IsZero returns true if the float is zero.
 // For boolean values, false (0) is zero, true (1) is not zero.
 func (f *Float) IsZero() bool {
-	return f.Float64() == 0
+	val, _ := f.Float64()
+	return val == 0
 }
 
 // IsNegative returns true if the float is negative.
@@ -194,6 +195,16 @@ func (f *Float) IsNegative() bool {
 	return f.n < 0
 }
 
+// IsString returns true if this number represents a string value.
+func (f *Float) IsString() bool {
+	return false
+}
+
+// IsSymbol returns true if this number represents a symbol.
+func (f *Float) IsSymbol() bool {
+	return false
+}
+
 // Compare returns -1, 0, or 1 if this float is less than, equal to, or greater than another.
 func (f *Float) Compare(other Number) (int, error) {
 	otherF, err := other.Float64()
@@ -373,6 +384,16 @@ func (r *Rat) IsNegative() bool {
 	return r.n.Sign() < 0
 }
 
+// IsString returns true if this number represents a string value.
+func (r *Rat) IsString() bool {
+	return false
+}
+
+// IsSymbol returns true if this number represents a symbol.
+func (r *Rat) IsSymbol() bool {
+	return false
+}
+
 // Compare returns -1, 0, or 1 if this rational is less than, equal to, or greater than another.
 func (r *Rat) Compare(other Number) (int, error) {
 	otherRat, ok := other.(*Rat)
@@ -393,7 +414,8 @@ func ToRat(n Number) *big.Rat {
 
 // ToFloat converts a Number to float64.
 func ToFloat(n Number) float64 {
-	return n.Float64()
+	val, _ := n.Float64()
+	return val
 }
 
 // StringNum represents a string value on the stack for variable names.
@@ -433,6 +455,7 @@ func (s *StringNum) IsNegative() bool                 { return false }
 func (s *StringNum) Compare(other Number) (int, error) { return 0, fmt.Errorf("string not supported for comparison") }
 func (s *StringNum) Bool() (bool, error)              { return false, fmt.Errorf("string not supported for Bool()") }
 func (s *StringNum) IsBool() bool                     { return false }
+func (s *StringNum) IsSymbol() bool                   { return false }
 
 // Symbol represents a variable symbol on the stack.
 // Symbols are created when:
@@ -493,6 +516,9 @@ func (s *Symbol) IsZero() bool {
 func (s *Symbol) IsNegative() bool {
 	return false
 }
+func (s *Symbol) IsString() bool {
+	return false
+}
 func (s *Symbol) Compare(other Number) (int, error) {
 	return 0, fmt.Errorf("symbol not supported for comparison")
 }
diff --git a/internal/rpn/rpn_parse.go b/internal/rpn/rpn_parse.go
index bf9a613..19e35fa 100644
--- a/internal/rpn/rpn_parse.go
+++ b/internal/rpn/rpn_parse.go
@@ -345,13 +345,17 @@ func (r *RPN) evaluate(input string, tokens []string) (string, error) {
 					if err != nil {
 						return "", fmt.Errorf("insufficient operands for %s: stack is empty", nextToken)
 					}
-					if err := r.vars.SetVariable(token, val.Float64()); err != nil {
+						valF, err := val.Float64()
+					if err != nil {
+						return "", fmt.Errorf("failed to get float64 value for variable %q: %w", token, err)
+					}
+					if err := r.vars.SetVariable(token, valF); err != nil {
 						return "", fmt.Errorf("failed to set variable %q: %w", token, err)
 					}
 					// Skip the operator token (next one) since we handled it inline
 					// We've consumed both tokens, so we're done
 					// Return confirmation message showing the assignment
-					return fmt.Sprintf("%s = %.10g", token, val.Float64()), nil
+						return fmt.Sprintf("%s = %.10g", token, valF), nil
 				} else if _, err := strconv.ParseFloat(token, 64); err != nil && isValidIdentifier(token) {
 					// This token is a variable name (not a number)
 					shouldPushName = true