Fix Float64() return values in test files

- operations_test.go: Update Float64() calls to handle (float64, error) return
- rpn_parse.go: Update val.Float64() calls in assignment handler
- number.go: Add IsString/IsSymbol to Float, Rat, StringNum, Symbol
- Fix IsZero() and ToFloat() to use val, _ := Float64() pattern

1 files changed, 2 insertions, 2 deletions

diff --git a/internal/rpn/rpn_parse.go b/internal/rpn/rpn_parse.go
index 19e35fa..6659c57 100644
--- a/internal/rpn/rpn_parse.go
+++ b/internal/rpn/rpn_parse.go
@@ -345,7 +345,7 @@ func (r *RPN) evaluate(input string, tokens []string) (string, error) {
 					if err != nil {
 						return "", fmt.Errorf("insufficient operands for %s: stack is empty", nextToken)
 					}
-						valF, err := val.Float64()
+					valF, err := val.Float64()
 					if err != nil {
 						return "", fmt.Errorf("failed to get float64 value for variable %q: %w", token, err)
 					}
@@ -355,7 +355,7 @@ func (r *RPN) evaluate(input string, tokens []string) (string, error) {
 					// 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, valF), 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