diff --git a/.forgejo/workflows/test.yaml b/.forgejo/workflows/test.yaml
new file mode 100644
index 0000000..8441947
--- /dev/null
+++ b/.forgejo/workflows/test.yaml
@@ -0,0 +1,20 @@
+name: Test
+
+on:
+  push:
+    branches:
+      - feature/*
+
+jobs:
+  build:
+    runs-on: docker
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: 1.22.4
+      - name: Build
+        run: |
+          make test
\ No newline at end of file
diff --git a/ucl/builtins.go b/ucl/builtins.go
index e984786..3b3a879 100644
--- a/ucl/builtins.go
+++ b/ucl/builtins.go
@@ -53,6 +53,120 @@ func addBuiltin(ctx context.Context, args invocationArgs) (object, error) {
 	return intObject(n), nil
 }
 
+func subBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if len(args.args) == 0 {
+		return intObject(0), nil
+	}
+
+	n := 0
+	for i, a := range args.args {
+		var p int
+		switch t := a.(type) {
+		case intObject:
+			p = int(t)
+		case strObject:
+			v, err := strconv.Atoi(string(t))
+			if err != nil {
+				return nil, fmt.Errorf("arg %v of 'sub' not convertable to an int", i)
+			}
+			p = v
+		default:
+			return nil, fmt.Errorf("arg %v of 'sub' not convertable to an int", i)
+		}
+		if i == 0 {
+			n = p
+		} else {
+			n -= p
+		}
+	}
+
+	return intObject(n), nil
+}
+
+func mupBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if len(args.args) == 0 {
+		return intObject(1), nil
+	}
+
+	n := 1
+	for i, a := range args.args {
+		switch t := a.(type) {
+		case intObject:
+			n *= int(t)
+		case strObject:
+			v, err := strconv.Atoi(string(t))
+			if err != nil {
+				return nil, fmt.Errorf("arg %v of 'mup' not convertable to an int", i)
+			}
+			n *= v
+		default:
+			return nil, fmt.Errorf("arg %v of 'mup' not convertable to an int", i)
+		}
+	}
+
+	return intObject(n), nil
+}
+
+func divBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if len(args.args) == 0 {
+		return intObject(1), nil
+	}
+
+	n := 1
+	for i, a := range args.args {
+		var p int
+		switch t := a.(type) {
+		case intObject:
+			p = int(t)
+		case strObject:
+			v, err := strconv.Atoi(string(t))
+			if err != nil {
+				return nil, fmt.Errorf("arg %v of 'div' not convertable to an int", i)
+			}
+			p = v
+		default:
+			return nil, fmt.Errorf("arg %v of 'div' not convertable to an int", i)
+		}
+		if i == 0 {
+			n = p
+		} else {
+			n /= p
+		}
+	}
+
+	return intObject(n), nil
+}
+
+func modBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if len(args.args) == 0 {
+		return intObject(0), nil
+	}
+
+	n := 0
+	for i, a := range args.args {
+		var p int
+		switch t := a.(type) {
+		case intObject:
+			p = int(t)
+		case strObject:
+			v, err := strconv.Atoi(string(t))
+			if err != nil {
+				return nil, fmt.Errorf("arg %v of 'mod' not convertable to an int", i)
+			}
+			p = v
+		default:
+			return nil, fmt.Errorf("arg %v of 'mod' not convertable to an int", i)
+		}
+		if i == 0 {
+			n = p
+		} else {
+			n %= p
+		}
+	}
+
+	return intObject(n), nil
+}
+
 func setBuiltin(ctx context.Context, args invocationArgs) (object, error) {
 	if err := args.expectArgn(2); err != nil {
 		return nil, err
@@ -88,19 +202,223 @@ func eqBuiltin(ctx context.Context, args invocationArgs) (object, error) {
 	l := args.args[0]
 	r := args.args[1]
 
-	switch lv := l.(type) {
-	case strObject:
-		if rv, ok := r.(strObject); ok {
-			return boolObject(lv == rv), nil
+	return boolObject(objectsEqual(l, r)), nil
+}
+
+func neBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(2); err != nil {
+		return nil, err
+	}
+
+	l := args.args[0]
+	r := args.args[1]
+
+	return boolObject(!objectsEqual(l, r)), nil
+}
+
+func ltBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(2); err != nil {
+		return nil, err
+	}
+
+	isLess, err := objectsLessThan(args.args[0], args.args[1])
+	if err != nil {
+		return nil, err
+	}
+	return boolObject(isLess), nil
+}
+
+func leBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(2); err != nil {
+		return nil, err
+	}
+
+	isLess, err := objectsLessThan(args.args[0], args.args[1])
+	if err != nil {
+		return nil, err
+	}
+	return boolObject(isLess || objectsEqual(args.args[0], args.args[1])), nil
+}
+
+func gtBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(2); err != nil {
+		return nil, err
+	}
+
+	isGreater, err := objectsLessThan(args.args[1], args.args[0])
+	if err != nil {
+		return nil, err
+	}
+	return boolObject(isGreater), nil
+}
+
+func geBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(2); err != nil {
+		return nil, err
+	}
+
+	isGreater, err := objectsLessThan(args.args[1], args.args[0])
+	if err != nil {
+		return nil, err
+	}
+	return boolObject(isGreater || objectsEqual(args.args[0], args.args[1])), nil
+}
+
+func andBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(2); err != nil {
+		return nil, err
+	}
+
+	for _, a := range args.args {
+		if a == nil || !a.Truthy() {
+			return boolObject(false), nil
 		}
-	case intObject:
-		if rv, ok := r.(intObject); ok {
-			return boolObject(lv == rv), nil
+	}
+	return args.args[len(args.args)-1], nil
+}
+
+func orBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(2); err != nil {
+		return nil, err
+	}
+
+	for _, a := range args.args {
+		if a != nil && a.Truthy() {
+			return a, nil
 		}
 	}
 	return boolObject(false), nil
 }
 
+func notBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(1); err != nil {
+		return nil, err
+	}
+
+	return boolObject(!args.args[0].Truthy()), nil
+}
+
+var errObjectsNotEqual = errors.New("objects not equal")
+
+func objectsEqual(l, r object) bool {
+	if l == nil || r == nil {
+		return l == nil && r == nil
+	}
+
+	switch lv := l.(type) {
+	case strObject:
+		if rv, ok := r.(strObject); ok {
+			return lv == rv
+		}
+	case intObject:
+		if rv, ok := r.(intObject); ok {
+			return lv == rv
+		}
+	case boolObject:
+		if rv, ok := r.(boolObject); ok {
+			return lv == rv
+		}
+	case listable:
+		rv, ok := r.(listable)
+		if !ok {
+			return false
+		}
+
+		if lv.Len() != rv.Len() {
+			return false
+		}
+		for i := 0; i < lv.Len(); i++ {
+			if !objectsEqual(lv.Index(i), rv.Index(i)) {
+				return false
+			}
+		}
+		return true
+	case hashable:
+		rv, ok := r.(hashable)
+		if !ok {
+			return false
+		}
+
+		if lv.Len() != rv.Len() {
+			return false
+		}
+		if err := lv.Each(func(k string, lkv object) error {
+			rkv := rv.Value(k)
+			if rkv == nil {
+				return errObjectsNotEqual
+			} else if !objectsEqual(lkv, rkv) {
+				return errObjectsNotEqual
+			}
+			return nil
+		}); err != nil {
+			return false
+		}
+		return true
+	case OpaqueObject:
+		rv, ok := r.(OpaqueObject)
+		if !ok {
+			return false
+		}
+
+		return lv.v == rv.v
+	}
+	return false
+}
+
+func objectsLessThan(l, r object) (bool, error) {
+	switch lv := l.(type) {
+	case strObject:
+		if rv, ok := r.(strObject); ok {
+			return lv < rv, nil
+		}
+	case intObject:
+		if rv, ok := r.(intObject); ok {
+			return lv < rv, nil
+		}
+	}
+	return false, errors.New("objects are not comparable")
+}
+
+func strBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(1); err != nil {
+		return nil, err
+	}
+
+	if args.args[0] == nil {
+		return strObject(""), nil
+	}
+
+	return strObject(args.args[0].String()), nil
+}
+
+func intBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(1); err != nil {
+		return nil, err
+	}
+
+	if args.args[0] == nil {
+		return intObject(0), nil
+	}
+
+	switch v := args.args[0].(type) {
+	case intObject:
+		return v, nil
+	case strObject:
+		i, err := strconv.Atoi(string(v))
+		if err != nil {
+			return nil, errors.New("cannot convert to int")
+		}
+		return intObject(i), nil
+	case boolObject:
+		if v {
+			return intObject(1), nil
+		}
+		return intObject(0), nil
+	}
+
+	return nil, errors.New("cannot convert to int")
+}
+
 func concatBuiltin(ctx context.Context, args invocationArgs) (object, error) {
 	var sb strings.Builder
 
@@ -114,20 +432,6 @@ func concatBuiltin(ctx context.Context, args invocationArgs) (object, error) {
 	return strObject(sb.String()), nil
 }
 
-//
-//func catBuiltin(ctx context.Context, args invocationArgs) (object, error) {
-//	if err := args.expectArgn(1); err != nil {
-//		return nil, err
-//	}
-//
-//	filename, err := args.stringArg(0)
-//	if err != nil {
-//		return nil, err
-//	}
-//
-//	return &fileLinesStream{filename: filename}, nil
-//}
-
 func callBuiltin(ctx context.Context, args invocationArgs) (object, error) {
 	if err := args.expectArgn(1); err != nil {
 		return nil, err
diff --git a/ucl/inst.go b/ucl/inst.go
index a4d1128..a5f35ed 100644
--- a/ucl/inst.go
+++ b/ucl/inst.go
@@ -61,7 +61,24 @@ func New(opts ...InstOption) *Inst {
 	rootEC.addCmd("reduce", invokableFunc(reduceBuiltin))
 
 	rootEC.addCmd("eq", invokableFunc(eqBuiltin))
+	rootEC.addCmd("ne", invokableFunc(neBuiltin))
+	rootEC.addCmd("gt", invokableFunc(gtBuiltin))
+	rootEC.addCmd("ge", invokableFunc(geBuiltin))
+	rootEC.addCmd("lt", invokableFunc(ltBuiltin))
+	rootEC.addCmd("le", invokableFunc(leBuiltin))
+
+	rootEC.addCmd("str", invokableFunc(strBuiltin))
+	rootEC.addCmd("int", invokableFunc(intBuiltin))
+
 	rootEC.addCmd("add", invokableFunc(addBuiltin))
+	rootEC.addCmd("sub", invokableFunc(subBuiltin))
+	rootEC.addCmd("mup", invokableFunc(mupBuiltin))
+	rootEC.addCmd("div", invokableFunc(divBuiltin))
+	rootEC.addCmd("mod", invokableFunc(modBuiltin))
+
+	rootEC.addCmd("and", invokableFunc(andBuiltin))
+	rootEC.addCmd("or", invokableFunc(orBuiltin))
+	rootEC.addCmd("not", invokableFunc(notBuiltin))
 
 	rootEC.addCmd("cat", invokableFunc(concatBuiltin))
 	rootEC.addCmd("break", invokableFunc(breakBuiltin))
@@ -72,10 +89,6 @@ func New(opts ...InstOption) *Inst {
 	rootEC.addMacro("foreach", macroFunc(foreachBuiltin))
 	rootEC.addMacro("proc", macroFunc(procBuiltin))
 
-	//rootEC.addCmd("testTimebomb", invokableStreamFunc(errorTestBuiltin))
-
-	rootEC.setOrDefineVar("hello", strObject("world"))
-
 	inst := &Inst{
 		out:    os.Stdout,
 		rootEC: rootEC,
@@ -88,6 +101,14 @@ func New(opts ...InstOption) *Inst {
 	return inst
 }
 
+func (inst *Inst) SetVar(name string, value any) {
+	obj, err := fromGoValue(value)
+	if err != nil {
+		return
+	}
+	inst.rootEC.setOrDefineVar(name, obj)
+}
+
 func (inst *Inst) Out() io.Writer {
 	if inst.out == nil {
 		return os.Stdout
diff --git a/ucl/objs.go b/ucl/objs.go
index 5527c85..1fa18e0 100644
--- a/ucl/objs.go
+++ b/ucl/objs.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"reflect"
 	"strconv"
+	"strings"
 
 	"github.com/lmika/gopkgs/fp/slices"
 )
@@ -51,7 +52,22 @@ func (s listObject) Index(i int) object {
 type hashObject map[string]object
 
 func (s hashObject) String() string {
-	return fmt.Sprintf("%v", map[string]object(s))
+	if len(s) == 0 {
+		return "[:]"
+	}
+
+	sb := strings.Builder{}
+	sb.WriteString("[")
+	for k, v := range s {
+		if sb.Len() != 1 {
+			sb.WriteString(" ")
+		}
+		sb.WriteString(k)
+		sb.WriteString(":")
+		sb.WriteString(v.String())
+	}
+	sb.WriteString("]")
+	return sb.String()
 }
 
 func (s hashObject) Truthy() bool {
@@ -99,9 +115,9 @@ type boolObject bool
 
 func (b boolObject) String() string {
 	if b {
-		return "(true)"
+		return "true"
 	}
-	return "(false))"
+	return "false"
 }
 
 func (b boolObject) Truthy() bool {
@@ -118,6 +134,8 @@ func toGoValue(obj object) (interface{}, bool) {
 		return string(v), true
 	case intObject:
 		return int(v), true
+	case boolObject:
+		return bool(v), true
 	case listObject:
 		xs := make([]interface{}, 0, len(v))
 		for _, va := range v {
@@ -159,6 +177,8 @@ func fromGoValue(v any) (object, error) {
 		return strObject(t), nil
 	case int:
 		return intObject(t), nil
+	case bool:
+		return boolObject(t), nil
 	}
 
 	return fromGoReflectValue(reflect.ValueOf(v))
diff --git a/ucl/testbuiltins_test.go b/ucl/testbuiltins_test.go
index 34e0220..7d0ae1c 100644
--- a/ucl/testbuiltins_test.go
+++ b/ucl/testbuiltins_test.go
@@ -229,16 +229,16 @@ func TestBuiltins_Break(t *testing.T) {
 		expr string
 		want string
 	}{
-		//{desc: "break unconditionally returning nothing", expr: `
-		//	foreach ["1" "2" "3"] { |v|
-		//		break
-		//		echo $v
-		//	}`, want: "(nil)\n"},
-		//{desc: "break conditionally returning nothing", expr: `
-		//	foreach ["1" "2" "3"] { |v|
-		//		echo $v
-		//		if (eq $v "2") { break }
-		//	}`, want: "1\n2\n(nil)\n"},
+		{desc: "break unconditionally returning nothing", expr: `
+			foreach ["1" "2" "3"] { |v|
+				break
+				echo $v
+			}`, want: "(nil)\n"},
+		{desc: "break conditionally returning nothing", expr: `
+			foreach ["1" "2" "3"] { |v|
+				echo $v
+				if (eq $v "2") { break }
+			}`, want: "1\n2\n(nil)\n"},
 		{desc: "break inner loop only returning nothing", expr: `
 			foreach ["a" "b"] { |u|
 				foreach ["1" "2" "3"] { |v|
@@ -246,11 +246,11 @@ func TestBuiltins_Break(t *testing.T) {
 					if (eq $v "2") { break }
 				}
 			}`, want: "a1\na2\nb1\nb2\n(nil)\n"},
-		//{desc: "break returning value", expr: `
-		//	echo (foreach ["1" "2" "3"] { |v|
-		//		echo $v
-		//		if (eq $v "2") { break "hello" }
-		//	})`, want: "1\n2\nhello\n(nil)\n"},
+		{desc: "break returning value", expr: `
+			echo (foreach ["1" "2" "3"] { |v|
+				echo $v
+				if (eq $v "2") { break "hello" }
+			})`, want: "1\n2\nhello\n(nil)\n"},
 	}
 
 	for _, tt := range tests {
@@ -891,3 +891,342 @@ func TestBuiltins_Reduce(t *testing.T) {
 		})
 	}
 }
+
+func TestBuiltins_LtLeGtLe(t *testing.T) {
+	tests := []struct {
+		desc    string
+		expr    string
+		want    bool
+		wantErr bool
+	}{
+		{desc: "str 1 - lt", expr: `lt "hello" "world"`, want: true},
+		{desc: "str 1 - le", expr: `le "hello" "world"`, want: true},
+		{desc: "str 1 - gt", expr: `gt "hello" "world"`, want: false},
+		{desc: "str 1 - ge", expr: `ge "hello" "world"`, want: false},
+		{desc: "str 2 - lt", expr: `lt "zzzzz" "world"`, want: false},
+		{desc: "str 2 - le", expr: `le "zzzzz" "world"`, want: false},
+		{desc: "str 2 - gt", expr: `gt "zzzzz" "world"`, want: true},
+		{desc: "str 2 - ge", expr: `ge "zzzzz" "world"`, want: true},
+		{desc: "str 3 - lt", expr: `lt "hello" "hello"`, want: false},
+		{desc: "str 3 - le", expr: `le "hello" "hello"`, want: true},
+		{desc: "str 3 - gt", expr: `gt "hello" "hello"`, want: false},
+		{desc: "str 3 - ge", expr: `ge "hello" "hello"`, want: true},
+
+		{desc: "int 1 - lt", expr: `lt 5 8`, want: true},
+		{desc: "int 1 - le", expr: `le 5 8`, want: true},
+		{desc: "int 1 - gt", expr: `gt 5 8`, want: false},
+		{desc: "int 1 - ge", expr: `ge 5 8`, want: false},
+		{desc: "int 2 - lt", expr: `lt 5 -8`, want: false},
+		{desc: "int 2 - le", expr: `le 5 -8`, want: false},
+		{desc: "int 2 - gt", expr: `gt 5 -8`, want: true},
+		{desc: "int 2 - ge", expr: `ge 5 -8`, want: true},
+		{desc: "int 3 - lt", expr: `lt 5 5`, want: false},
+		{desc: "int 3 - le", expr: `le 5 5`, want: true},
+		{desc: "int 3 - gt", expr: `gt 5 5`, want: false},
+		{desc: "int 3 - ge", expr: `ge 5 5`, want: true},
+
+		{desc: "not comparable 1", expr: `lt () ()`, wantErr: true},
+		{desc: "not comparable 2", expr: `lt $true $false`, wantErr: true},
+		{desc: "not comparable 3", expr: `lt [1 2 3] [2 3 4]`, wantErr: true},
+		{desc: "not comparable 4", expr: `lt ["1":2] ["2":3]`, wantErr: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ctx := context.Background()
+			outW := bytes.NewBuffer(nil)
+
+			inst := New(WithOut(outW), WithTestBuiltin())
+			inst.SetVar("true", true)
+			inst.SetVar("false", false)
+
+			eqRes, err := inst.Eval(ctx, tt.expr)
+
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, eqRes)
+			}
+		})
+	}
+}
+
+func TestBuiltins_EqNe(t *testing.T) {
+	tests := []struct {
+		desc string
+		expr string
+		want bool
+	}{
+		{desc: "equal strs 1", expr: `eq "hello" "hello"`, want: true},
+		{desc: "equal strs 2", expr: `eq "bla" "bla"`, want: true},
+		{desc: "equal strs 3", expr: `eq "" ""`, want: true},
+		{desc: "equal ints 1", expr: `eq 123 123`, want: true},
+		{desc: "equal ints 2", expr: `eq -21 -21`, want: true},
+		{desc: "equal ints 3", expr: `eq 0 0`, want: true},
+		{desc: "equal lists 1", expr: `eq [1 2 3] [1 2 3]`, want: true},
+		{desc: "equal lists 2", expr: `eq ["foo" "bar"] ["foo" "bar"]`, want: true},
+		{desc: "equal lists 3", expr: `eq [] []`, want: true},
+		{desc: "equal hashes 1", expr: `eq ["this":1 "that":"thing"] ["that":"thing" "this":1]`, want: true},
+		{desc: "equal hashes 2", expr: `eq ["foo":"bar"] ["foo":"bar"]`, want: true},
+		{desc: "equal bools 1", expr: `eq $true $true`, want: true},
+		{desc: "equal bools 2", expr: `eq $false $false`, want: true},
+		{desc: "equal nil 1", expr: `eq () ()`, want: true},
+		{desc: "equal opaque 1", expr: `eq $hello $hello`, want: true},
+		{desc: "equal opaque 2", expr: `eq $world $world`, want: true},
+
+		{desc: "not equal strs 1", expr: `eq "hello" "world"`, want: false},
+		{desc: "not equal strs 2", expr: `eq "bla" "BLA"`, want: false},
+		{desc: "not equal int 1", expr: `eq 131 313`, want: false},
+		{desc: "not equal int 2", expr: `eq -2 2`, want: false},
+		{desc: "not equal lists 1", expr: `eq [1 2 3] [1 2]`, want: false},
+		{desc: "not equal lists 2", expr: `eq ["123" "234"] [123 234]`, want: false},
+		{desc: "not equal hashes 1", expr: `eq ["this":1 "that":"thing"] ["that":"thing"]`, want: false},
+		{desc: "not equal hashes 2", expr: `eq ["this":1 "that":"thing"] ["this":1 "that":"thing" "other":"thing"]`, want: false},
+		{desc: "not equal hashes 3", expr: `eq ["this":1 "that":"thing"] ["this":"1" "that":"other"]`, want: false},
+		{desc: "not equal opaque 1", expr: `eq $hello $world`, want: false},
+		{desc: "not equal opaque 2", expr: `eq $hello "hello"`, want: false},
+
+		{desc: "not equal types 1", expr: `eq "123" 123`, want: false},
+		{desc: "not equal types 2", expr: `eq 0 ""`, want: false},
+		{desc: "not equal types 3", expr: `eq [] [:]`, want: false},
+		{desc: "not equal types 4", expr: `eq ["23"] "23"`, want: false},
+		{desc: "not equal types 5", expr: `eq $true ()`, want: false},
+		{desc: "not equal types 6", expr: `eq () $false`, want: false},
+		{desc: "not equal types 7", expr: `eq () "yes"`, want: false},
+		{desc: "not equal types 8", expr: `eq () $world`, want: false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			type testProxyObject struct {
+				v string
+			}
+
+			ctx := context.Background()
+			outW := bytes.NewBuffer(nil)
+
+			inst := New(WithOut(outW), WithTestBuiltin())
+			inst.SetVar("hello", Opaque(testProxyObject{v: "hello"}))
+			inst.SetVar("world", Opaque(testProxyObject{v: "world"}))
+			inst.SetVar("true", true)
+			inst.SetVar("false", false)
+
+			eqRes, err := inst.Eval(ctx, tt.expr)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, eqRes)
+
+			neRes, err := inst.Eval(ctx, strings.ReplaceAll(tt.expr, "eq", "ne"))
+			assert.NoError(t, err)
+			assert.Equal(t, !tt.want, neRes)
+		})
+	}
+}
+
+func TestBuiltins_Str(t *testing.T) {
+	tests := []struct {
+		desc string
+		expr string
+		want string
+	}{
+		{desc: "str", expr: `str "hello"`, want: "hello"},
+		{desc: "int", expr: `str 123`, want: "123"},
+		{desc: "bool 1", expr: `str (eq 1 1)`, want: "true"},
+		{desc: "bool 2", expr: `str (eq 1 0)`, want: "false"},
+		{desc: "list 1", expr: `str [1 2 3]`, want: "[1 2 3]"},
+		{desc: "list 2", expr: `str []`, want: "[]"},
+		{desc: "dict 1", expr: `str ["hello":"world"]`, want: `[hello:world]`},
+		{desc: "dict 2", expr: `str [:]`, want: "[:]"},
+		{desc: "nil", expr: `str ()`, want: ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ctx := context.Background()
+			outW := bytes.NewBuffer(nil)
+
+			inst := New(WithOut(outW), WithTestBuiltin())
+
+			eqRes, err := inst.Eval(ctx, tt.expr)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, eqRes)
+		})
+	}
+}
+
+func TestBuiltins_Int(t *testing.T) {
+	tests := []struct {
+		desc    string
+		expr    string
+		want    int
+		wantErr bool
+	}{
+		{desc: "str 1", expr: `int "123"`, want: 123},
+		{desc: "str 2", expr: `int "31452"`, want: 31452},
+		{desc: "str 3", expr: `int "-21"`, want: -21},
+		{desc: "int 1", expr: `int 123`, want: 123},
+		{desc: "int 2", expr: `int -21`, want: -21},
+		{desc: "bool 1", expr: `int (eq 1 1)`, want: 1},
+		{desc: "bool 2", expr: `int (eq 1 0)`, want: 0},
+		{desc: "nil", expr: `int ()`, want: 0},
+
+		{desc: "list 1", expr: `int [1 2 3]`, wantErr: true},
+		{desc: "list 2", expr: `int []`, wantErr: true},
+		{desc: "dict 1", expr: `int ["hello":"world"]`, wantErr: true},
+		{desc: "dict 2", expr: `int [:]`, wantErr: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ctx := context.Background()
+			outW := bytes.NewBuffer(nil)
+
+			inst := New(WithOut(outW), WithTestBuiltin())
+
+			eqRes, err := inst.Eval(ctx, tt.expr)
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, eqRes)
+			}
+		})
+	}
+}
+
+func TestBuiltins_AddSubMupDivMod(t *testing.T) {
+	tests := []struct {
+		desc    string
+		expr    string
+		want    int
+		wantErr bool
+	}{
+		{desc: "add 1", expr: `add 1 2`, want: 3},
+		{desc: "add 2", expr: `add "3" 5`, want: 8},
+		{desc: "add 3", expr: `add 1 "2" 8`, want: 11},
+		{desc: "add 4", expr: `add 1`, want: 1},
+		{desc: "add 5", expr: `add`, want: 0},
+		{desc: "sub 1", expr: `sub 9 3`, want: 6},
+		{desc: "sub 2", expr: `sub 2 "5"`, want: -3},
+		{desc: "sub 3", expr: `sub 8 1 8`, want: -1},
+		{desc: "sub 4", expr: `sub 4`, want: 4},
+		{desc: "sub 5", expr: `sub`, want: 0},
+		{desc: "mup 1", expr: `mup 2 4`, want: 8},
+		{desc: "mup 2", expr: `mup 3 "4" 5`, want: 60},
+		{desc: "mup 3", expr: `mup 7`, want: 7},
+		{desc: "mup 4", expr: `mup`, want: 1},
+		{desc: "div 1", expr: `div 8 4`, want: 2},
+		{desc: "div 2", expr: `div "7" 4`, want: 1},
+		{desc: "div 3", expr: `div 7`, want: 7},
+		{desc: "div 4", expr: `div`, want: 1},
+		{desc: "mod 1", expr: `mod 2 3`, want: 2},
+		{desc: "mod 2", expr: `mod "7" 4`, want: 3},
+		{desc: "mod 3", expr: `mod 8 4`, want: 0},
+		{desc: "mod 4", expr: `mod 3`, want: 3},
+		{desc: "mod 5", expr: `mod`, want: 0},
+
+		{desc: "add err", expr: `add [] [:]`, wantErr: true},
+		{desc: "sub err", expr: `sub [] [:]`, wantErr: true},
+		{desc: "mup err", expr: `mup [] [:]`, wantErr: true},
+		{desc: "div err", expr: `div [] [:]`, wantErr: true},
+		{desc: "mod err", expr: `mod [] [:]`, wantErr: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ctx := context.Background()
+			outW := bytes.NewBuffer(nil)
+
+			inst := New(WithOut(outW), WithTestBuiltin())
+
+			eqRes, err := inst.Eval(ctx, tt.expr)
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, eqRes)
+			}
+		})
+	}
+}
+
+func TestBuiltins_AndOrNot(t *testing.T) {
+	tests := []struct {
+		desc    string
+		expr    string
+		want    any
+		wantErr bool
+	}{
+		{desc: "and 1", expr: `and $true $true`, want: true},
+		{desc: "and 2", expr: `and $false $true`, want: false},
+		{desc: "and 3", expr: `and $false $false`, want: false},
+		{desc: "or 1", expr: `or $true $true`, want: true},
+		{desc: "or 2", expr: `or $false $true`, want: true},
+		{desc: "or 3", expr: `or $false $false`, want: false},
+		{desc: "not 1", expr: `not $true`, want: false},
+		{desc: "not 2", expr: `not $false`, want: true},
+		{desc: "not 3", expr: `not $false $true`, want: true},
+
+		{desc: "short circuit and 1", expr: `and "hello" "world"`, want: "world"},
+		{desc: "short circuit and 2", expr: `and () "world"`, want: false},
+		{desc: "short circuit or 1", expr: `or "hello" "world"`, want: "hello"},
+		{desc: "short circuit or 2", expr: `or () "world"`, want: "world"},
+
+		{desc: "bad and 1", expr: `and "one"`, wantErr: true},
+		{desc: "bad and 2", expr: `and`, wantErr: true},
+		{desc: "bad or 1", expr: `or "one"`, wantErr: true},
+		{desc: "bad or 2", expr: `or`, wantErr: true},
+		{desc: "bad not 2", expr: `not`, wantErr: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ctx := context.Background()
+			outW := bytes.NewBuffer(nil)
+
+			inst := New(WithOut(outW), WithTestBuiltin())
+			inst.SetVar("true", true)
+			inst.SetVar("false", false)
+
+			eqRes, err := inst.Eval(ctx, tt.expr)
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, eqRes)
+			}
+		})
+	}
+}
+
+func TestBuiltins_Cat(t *testing.T) {
+	tests := []struct {
+		desc string
+		expr string
+		want any
+	}{
+		{desc: "cat 1", expr: `cat "hello, " "world"`, want: "hello, world"},
+		{desc: "cat 2", expr: `cat "hello, " "world " "and stuff"`, want: "hello, world and stuff"},
+		{desc: "cat 3", expr: `cat "int = " 123`, want: "int = 123"},
+		{desc: "cat 4", expr: `cat "bool = " $true`, want: "bool = true"},
+		{desc: "cat 5", expr: `cat "array = " []`, want: "array = []"},
+		{desc: "cat 6", expr: `cat "array = " [1 3 2 4]`, want: "array = [1 3 2 4]"},
+		{desc: "cat 7", expr: `cat 1 $true 3 [4]`, want: "1true3[4]"},
+		{desc: "cat 8", expr: `cat`, want: ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ctx := context.Background()
+			outW := bytes.NewBuffer(nil)
+
+			inst := New(WithOut(outW), WithTestBuiltin())
+			inst.SetVar("true", true)
+			inst.SetVar("false", false)
+
+			eqRes, err := inst.Eval(ctx, tt.expr)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, eqRes)
+		})
+	}
+}