fix(ast): avoid panic in ConstantNode.String on non-JSON floats

ast/print.go

@@ -43,7 +43,11 @@ func (n *ConstantNode) String() string {
 	}
 	b, err := json.Marshal(n.Value)
 	if err != nil {
-		panic(err)
+		// json.Marshal rejects values such as NaN and ±Inf, which can
+		// reach here after constant folding (e.g. an array literal like
+		// [0/0]). Fall back to a non-panicking representation instead of
+		// crashing the caller (the optimizer runs this during Compile).
+		return fmt.Sprintf("%v", n.Value)
 	}
 	return string(b)
 }

ast/print_test.go

@@ -1,6 +1,7 @@
 package ast_test
 
 import (
+	"math"
 	"testing"
 
 	"github.com/expr-lang/expr/internal/testify/assert"
@@ -120,6 +121,8 @@ func TestPrint_ConstantNode(t *testing.T) {
 		{"a", `"a"`},
 		{[]int{1, 2, 3}, `[1,2,3]`},
 		{map[string]int{"a": 1}, `{"a":1}`},
+		{[]any{math.NaN()}, `[NaN]`},
+		{math.Inf(1), `+Inf`},
 	}
 
 	for _, tt := range tests {

optimizer/optimizer_test.go

@@ -458,3 +458,17 @@ func TestOptimize_predicate_combination_nested(t *testing.T) {
 
 	assert.Equal(t, ast.Dump(expected), ast.Dump(tree.Node))
 }
+
+func TestOptimize_predicate_combination_with_non_json_float(t *testing.T) {
+	// Constant folding turns [0/0] into a ConstantNode holding []any{NaN}.
+	// predicateCombination compares the collection arguments via String(),
+	// which must not panic on values json.Marshal rejects (NaN, ±Inf).
+	for _, code := range []string{
+		`any([0/0], # > 0) || any([0/0], # > 0)`,
+		`all([1/0], # > 0) && all([1/0], # > 0)`,
+		`none([0/0], # > 0) && none([0/0], # > 0)`,
+	} {
+		_, err := expr.Compile(code)
+		require.NoError(t, err, code)
+	}
+}