diff --git a/internal/rosa/azalea/azalea_test.go b/internal/rosa/azalea/azalea_test.go
index f2dec252..73330412 100644
--- a/internal/rosa/azalea/azalea_test.go
+++ b/internal/rosa/azalea/azalea_test.go
@@ -154,3 +154,16 @@ func TestParse(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkParse(b *testing.B) {
+	r := strings.NewReader(sample)
+	for b.Loop() {
+		if _, err := Parse(r); err != nil {
+			b.Fatal(err)
+		}
+
+		b.StopTimer()
+		r.Reset(sample)
+		b.StartTimer()
+	}
+}
diff --git a/internal/rosa/azalea/evaluate.go b/internal/rosa/azalea/evaluate.go
new file mode 100644
index 00000000..6ec30915
--- /dev/null
+++ b/internal/rosa/azalea/evaluate.go
@@ -0,0 +1,305 @@
+package azalea
+
+import (
+	"errors"
+	"fmt"
+	"maps"
+	"reflect"
+	"unique"
+)
+
+// Value are types supported by the language.
+type Value interface {
+	bool | int64 | string | []string | [][2]string
+}
+
+type (
+	// FArg is an argument passed to [F].
+	FArg struct {
+		K unique.Handle[Ident]
+		V any
+		R bool
+	}
+	// FArgs are arguments passed to [F].
+	FArgs []FArg
+
+	// F is the implementation of a [Func].
+	F struct {
+		F func(isPackage bool, args FArgs) (v string, set bool, err error)
+		V map[unique.Handle[Ident]]any
+	}
+)
+
+// Apply applies named arguments and rejects unused arguments.
+func (args FArgs) Apply(v map[unique.Handle[Ident]]any) error {
+	for _, arg := range args {
+		if arg.V == nil {
+			// unset
+			continue
+		}
+
+		r, ok := v[arg.K]
+		if !ok {
+			if arg.R {
+				continue
+			}
+			return UndefinedError(arg.K.Value())
+		}
+		err := storeE(r, arg.V)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// A Frame refers to local variables and debugging information.
+type Frame struct {
+	// Local constants.
+	Val map[unique.Handle[Ident]]any
+	// Functions.
+	Func map[unique.Handle[Ident]]F
+}
+
+// UnsupportedExprError is an expression with invalid concrete type.
+type UnsupportedExprError struct{ E any }
+
+func (e UnsupportedExprError) Error() string {
+	return fmt.Sprintf("unsupported expression %#v", e.E)
+}
+
+// UndefinedError is an identifier not defined in any stack frame visible to the
+// expression containing it.
+type UndefinedError Ident
+
+func (e UndefinedError) Error() string {
+	return "undefined: " + string(e)
+}
+
+// evaluate is evaluateAny with a type parameter.
+func evaluate[T Value](s []Frame, expr any, rp *T) bool {
+	return evaluateAny(s, expr, rp)
+}
+
+// TypeError is an unexpected type during evaluation.
+type TypeError struct {
+	Concrete, Asserted reflect.Type
+}
+
+func (e TypeError) Error() string {
+	return "expected " + e.Asserted.String() + ", got " + e.Concrete.String()
+}
+
+func (e TypeError) Is(err error) bool {
+	var v TypeError
+	return errors.As(err, &v) &&
+		e.Asserted == v.Asserted &&
+		e.Concrete == v.Concrete
+}
+
+// storeE is a convenience function to set the value of a result pointer.
+func storeE(rp any, r any) error {
+	pv := reflect.ValueOf(rp).Elem()
+	v := reflect.ValueOf(r)
+	pt, vt := pv.Type(), v.Type()
+	if !vt.AssignableTo(pt) {
+		return TypeError{vt, pt}
+	}
+	pv.Set(v)
+	return nil
+}
+
+// store is like storeE, but panics if error is non-nil.
+func store[T Value](rp any, r T) {
+	err := storeE(rp, r)
+	if err != nil {
+		panic(err)
+	}
+}
+
+// EvaluationError is an error and the expression it occurred in.
+type EvaluationError struct {
+	Expr any
+	Err  error
+}
+
+// Unwrap returns the underlying error.
+func (e EvaluationError) Unwrap() error { return e.Err }
+
+// Error returns a very long error description that should not be presented
+// to the user directly.
+func (e EvaluationError) Error() string {
+	return fmt.Sprintf("expression %#v: %v", e.Expr, e.Err)
+}
+
+// evaluateAny implements [Evaluate].
+func evaluateAny(s []Frame, expr, rp any) bool {
+	defer func() {
+		r := recover()
+		if r == nil {
+			return
+		}
+
+		err, ok := r.(error)
+		if !ok {
+			panic(r)
+		}
+
+		if _, ok = err.(EvaluationError); ok {
+			panic(err)
+		}
+		panic(EvaluationError{expr, err})
+	}()
+
+	switch e := expr.(type) {
+	case Int:
+		store(rp, int64(e))
+		return true
+
+	case String:
+		store(rp, string(e))
+		return true
+
+	case Ident:
+		var (
+			v  any
+			ok bool
+		)
+		for i := range s {
+			v, ok = s[len(s)-1-i].Val[unique.Make(e)]
+			if ok {
+				break
+			}
+		}
+		if !ok {
+			panic(UndefinedError(e))
+		}
+		if err := storeE(rp, v); err != nil {
+			panic(err)
+		}
+		return true
+
+	case Val:
+		if len(e) == 1 {
+			switch v := e[0].(type) {
+			case Ident:
+				switch v {
+				case "unset":
+					return false
+				case "true":
+					store(rp, true)
+					return true
+				case "false":
+					store(rp, false)
+					return true
+				default:
+					return evaluateAny(s, v, rp)
+				}
+
+			default:
+				return evaluateAny(s, e[0], rp)
+			}
+		}
+		var v string
+		for i := range e {
+			var _r string
+			if evaluate(s, e[i], &_r) {
+				v += _r
+			}
+		}
+		store(rp, v)
+		return true
+
+	case Array:
+		r := make([]string, 0, len(e))
+		for i := range e {
+			var _r string
+			if evaluate(s, e[i], &_r) {
+				r = append(r, _r)
+			}
+		}
+		store(rp, r)
+		return true
+
+	case []KV:
+		r := make([][2]string, 0, len(e))
+		for i := range e {
+			var _r string
+			if e[i].V == nil || evaluate(s, e[i].V, &_r) {
+				r = append(r, [2]string{string(e[i].K), _r})
+			}
+		}
+		store(rp, r)
+		return true
+
+	case Func:
+		var (
+			f  F
+			ok bool
+		)
+		for i := range s {
+			f, ok = s[len(s)-1-i].Func[unique.Make(e.Ident)]
+			if ok {
+				break
+			}
+		}
+		if !ok {
+			panic(UndefinedError(e.Ident))
+		}
+
+		argc := len(e.Args)
+		for _, arg := range e.Args {
+			argc += len(arg.K) - 1
+		}
+		fargs := make([]FArg, 0, len(e.Args))
+		s = append(s, Frame{Val: maps.Clone(f.V)})
+		fp := &s[len(s)-1]
+
+		for _, arg := range e.Args {
+			farg := FArg{R: arg.R}
+			if !evaluateAny(s, arg.V, &farg.V) {
+				farg.V = nil
+			}
+			for _, name := range arg.K {
+				h := unique.Make(name)
+				farg.K = h
+				fargs = append(fargs, farg)
+
+				if arg.R && farg.V != nil {
+					if fp.Val == nil {
+						fp.Val = make(map[unique.Handle[Ident]]any)
+					}
+					(*fp).Val[h] = farg.V
+				}
+			}
+		}
+
+		v, set, err := f.F(e.Package, fargs)
+		if err != nil {
+			panic(err)
+		}
+		store(rp, v)
+		return set
+
+	default:
+		panic(UnsupportedExprError{expr})
+	}
+}
+
+// Evaluate evaluates a statement and returns its value.
+func Evaluate[T Value](s []Frame, expr any) (v T, set bool, err error) {
+	defer func() {
+		r := recover()
+		if r == nil {
+			return
+		}
+
+		_err, ok := r.(error)
+		if !ok {
+			panic(r)
+		}
+		err = _err
+	}()
+	set = evaluate[T](s, expr, &v)
+	return
+}
diff --git a/internal/rosa/azalea/evaluate_test.go b/internal/rosa/azalea/evaluate_test.go
new file mode 100644
index 00000000..5943f34c
--- /dev/null
+++ b/internal/rosa/azalea/evaluate_test.go
@@ -0,0 +1,357 @@
+package azalea_test
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+	"strings"
+	"testing"
+	"unique"
+
+	. "hakurei.app/internal/rosa/azalea"
+)
+
+// makeStackCheck creates a stack with a single frame with a single function "f"
+// which calls the check function internally.
+func makeStackCheck(check func(args FArgs) (string, error)) []Frame {
+	return []Frame{{Func: map[unique.Handle[Ident]]F{
+		unique.Make(Ident("f")): {F: func(
+			isPackage bool,
+			args FArgs,
+		) (v string, set bool, err error) {
+			set = true
+			v, err = check(args)
+			if isPackage {
+				err = errors.New("unexpected package")
+			}
+			return
+		}},
+	}}}
+}
+
+// makeWantArgs makes a stack for validating the arguments of a single function "f".
+func makeWantArgs(want FArgs) []Frame {
+	return makeStackCheck(func(got FArgs) (string, error) {
+		if !reflect.DeepEqual(got, want) {
+			return "", fmt.Errorf("f: %#v, want %#v", got, want)
+		}
+		return "\xfc", nil
+	})
+}
+
+func TestEvaluate(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		data string
+		s    []Frame
+		want string
+		err  error
+	}{
+		{"apply unset", `f { v = unset; }`, makeStackCheck(func(
+			args FArgs,
+		) (v string, err error) {
+			v = "\xfd"
+			err = args.Apply(map[unique.Handle[Ident]]any{
+				unique.Make(Ident("v")): &v,
+			})
+			return
+		}), "\xfd", nil},
+
+		{"apply bad type", `f { v = 9; }`, makeStackCheck(func(
+			args FArgs,
+		) (v string, err error) {
+			v = "\xfd"
+			err = args.Apply(map[unique.Handle[Ident]]any{
+				unique.Make(Ident("v")): &v,
+			})
+			return
+		}), "", TypeError{
+			Concrete: reflect.TypeFor[int64](),
+			Asserted: reflect.TypeFor[string](),
+		}},
+
+		{"apply undefined", `f { v = 9; }`, makeStackCheck(func(
+			args FArgs,
+		) (v string, err error) {
+			v = "\xfd"
+			err = args.Apply(map[unique.Handle[Ident]]any{})
+			return
+		}), "", EvaluationError{
+			Expr: Func{
+				Ident: Ident("f"),
+				Args: []Arg{
+					{K: []Ident{"v"}, V: Val{Int(9)}},
+				},
+			},
+			Err: UndefinedError("v"),
+		}},
+
+		{"apply bound undefined", `f { _v* = "\x00"; v = _v; }`, makeStackCheck(func(
+			args FArgs,
+		) (v string, err error) {
+			v = "\xfd"
+			err = args.Apply(map[unique.Handle[Ident]]any{
+				unique.Make(Ident("v")): &v,
+			})
+			return
+		}), "\x00", nil},
+
+		{"undefined function", `f {}`, nil, "", EvaluationError{
+			Expr: Func{Ident: "f"},
+			Err:  UndefinedError("f"),
+		}},
+
+		{"error wrap deep", `f { v = nil; }`, makeStackCheck(func(
+			FArgs,
+		) (string, error) {
+			panic("unreachable")
+		}), "", EvaluationError{
+			Expr: Ident("nil"),
+			Err:  UndefinedError("nil"),
+		}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			var expr Func
+			if e, err := Parse(strings.NewReader(tc.data)); err != nil {
+				t.Fatal(err)
+			} else if len(e) != 1 {
+				t.Fatalf("got expression %#v", e)
+			} else {
+				expr = e[0].(Func)
+			}
+			r, set, err := Evaluate[string](tc.s, expr)
+			if set != (err == nil) {
+				t.Error("Evaluate: unexpected unset")
+			}
+
+			if r != tc.want {
+				t.Errorf("Evaluate: %q, want %q", r, tc.want)
+			}
+
+			var errEquals bool
+			if errors.As(err, new(TypeError)) {
+				errEquals = errors.Is(err, tc.err)
+			} else {
+				errEquals = reflect.DeepEqual(err, tc.err)
+			}
+			if !errEquals {
+				t.Errorf("Evaluate: error = %v, want %v", err, tc.err)
+			}
+		})
+	}
+}
+
+func TestEvaluateGCC(t *testing.T) {
+	t.Parallel()
+
+	var gcc Func
+	if e, err := Parse(strings.NewReader(sample)); err != nil {
+		t.Fatal(err)
+	} else {
+		gcc = e[0].(Func)
+	}
+
+	var got [4]FArgs
+	if r, set, err := Evaluate[string]([]Frame{{
+		Func: map[unique.Handle[Ident]]F{
+			unique.Make(Ident("gcc")): {F: func(
+				isPackage bool,
+				args FArgs,
+			) (v string, set bool, err error) {
+				v = "\x00"
+				if !isPackage {
+					err = errors.New("not a package")
+				}
+				set = true
+				got[0] = args
+				return
+			}, V: map[unique.Handle[Ident]]any{
+				unique.Make(Ident("binutils")):       "binutils",
+				unique.Make(Ident("mpc")):            "mpc",
+				unique.Make(Ident("zlib")):           "zlib",
+				unique.Make(Ident("libucontext")):    "libucontext",
+				unique.Make(Ident("kernel-headers")): "kernel-headers",
+			}},
+
+			unique.Make(Ident("remoteTar")): {F: func(
+				isPackage bool,
+				args FArgs,
+			) (v string, set bool, err error) {
+				if isPackage {
+					err = errors.New("unexpected package")
+					return
+				}
+
+				var url, checksum string
+				var compress int
+				if err = args.Apply(map[unique.Handle[Ident]]any{
+					unique.Make(Ident("url")):      &url,
+					unique.Make(Ident("checksum")): &checksum,
+					unique.Make(Ident("compress")): &compress,
+				}); err != nil {
+					return
+				}
+
+				if compress != 0xcafe {
+					err = fmt.Errorf("unexpected compress %#v", compress)
+				}
+				set = true
+				v = url + "?checksum=" + checksum
+				return
+			}, V: map[unique.Handle[Ident]]any{
+				unique.Make(Ident("gzip")): 0xcafe,
+			}},
+
+			unique.Make(Ident("make")): {F: func(
+				isPackage bool,
+				args FArgs,
+			) (v string, set bool, err error) {
+				v = "\x01"
+				if isPackage {
+					err = errors.New("unexpected package")
+				}
+				set = true
+				got[1] = args
+				return
+			}},
+
+			unique.Make(Ident("arch")): {F: func(
+				isPackage bool,
+				args FArgs,
+			) (v string, set bool, err error) {
+				set = false
+				if isPackage {
+					err = errors.New("unexpected package")
+				}
+				got[2] = args
+				return
+			}},
+
+			unique.Make(Ident("noop")): {F: func(
+				isPackage bool,
+				args FArgs,
+			) (v string, set bool, err error) {
+				set = false
+				if isPackage {
+					err = errors.New("unexpected package")
+				}
+				set = true
+				got[3] = args
+				return
+			}, V: map[unique.Handle[Ident]]any{
+				unique.Make(Ident("value")): "\xfd",
+			}},
+		},
+	}}, gcc); err != nil {
+		t.Fatal(err)
+	} else if r != "\x00" {
+		t.Fatalf("package: %q", r)
+	} else if !set {
+		t.Fatal("package: unset")
+	}
+
+	want := [...]FArgs{
+		{
+			{K: unique.Make(Ident("description")), V: "The GNU Compiler Collection"},
+			{K: unique.Make(Ident("website")), V: "https://www.gnu.org/software/gcc"},
+			{K: unique.Make(Ident("anitya")), V: int64(6502)},
+
+			{K: unique.Make(Ident("version")), V: "16.1.0", R: true},
+			{K: unique.Make(Ident("source")), V: "https://ftp.tsukuba.wide.ad.jp/software/gcc/releases/gcc-16.1.0/gcc-16.1.0.tar.gz?checksum=4ASoWbxaA2FW7PAB0zzHDPC5XnNhyaAyjtDPpGzceSLeYnEIXsNYZR3PA_Zu5P0K"},
+			{K: unique.Make(Ident("patches")), V: []string{"musl-off64_t-loff_t.patch", "musl-legacy-lfs.patch"}},
+
+			{K: unique.Make(Ident("exclusive")), V: true},
+			{K: unique.Make(Ident("exec")), V: "\x01"},
+
+			{K: unique.Make(Ident("inputs")), V: []string{
+				"binutils",
+				"mpc",
+				"zlib",
+				"libucontext",
+				"kernel-headers",
+			}},
+		},
+		{
+			{K: unique.Make(Ident("configure")), V: [][2]string{{"disable-multilib", ""}, {"enable-default-pie", ""}, {"disable-nls", ""}, {"with-gnu-as", ""}, {"with-gnu-ld", ""}, {"with-system-zlib", ""}, {"enable-languages", "c,c++,go"}, {"with-native-system-header-dir", "/system/include"}}},
+			{K: unique.Make(Ident("make")), V: []string{"BOOT_CFLAGS='-O2 -g'", "\x00", "bootstrap"}},
+			{K: unique.Make(Ident("skip-check")), V: true},
+		},
+		{
+			{K: unique.Make(Ident("amd64")), V: "''"},
+			{K: unique.Make(Ident("arm64")), V: "''"},
+			{K: unique.Make(Ident("default"))},
+		},
+		{{K: unique.Make(Ident("key")), V: "\xfd"}},
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("package: args = %#v, want %#v", got, want)
+	}
+}
+
+func BenchmarkEvaluate(b *testing.B) {
+	var gcc Func
+	if e, err := Parse(strings.NewReader(sample)); err != nil {
+		b.Fatal(err)
+	} else {
+		gcc = e[0].(Func)
+	}
+
+	s := []Frame{{
+		Func: map[unique.Handle[Ident]]F{
+			unique.Make(Ident("gcc")): {F: func(
+				bool,
+				FArgs,
+			) (v string, set bool, err error) {
+				return
+			}, V: map[unique.Handle[Ident]]any{
+				unique.Make(Ident("binutils")):       "binutils",
+				unique.Make(Ident("mpc")):            "mpc",
+				unique.Make(Ident("zlib")):           "zlib",
+				unique.Make(Ident("libucontext")):    "libucontext",
+				unique.Make(Ident("kernel-headers")): "kernel-headers",
+			}},
+
+			unique.Make(Ident("remoteTar")): {F: func(
+				bool,
+				FArgs,
+			) (v string, set bool, err error) {
+				return
+			}, V: map[unique.Handle[Ident]]any{
+				unique.Make(Ident("gzip")): 0xcafe,
+			}},
+
+			unique.Make(Ident("make")): {F: func(
+				bool,
+				FArgs,
+			) (v string, set bool, err error) {
+				return
+			}},
+
+			unique.Make(Ident("arch")): {F: func(
+				bool,
+				FArgs,
+			) (v string, set bool, err error) {
+				return
+			}},
+
+			unique.Make(Ident("noop")): {F: func(
+				bool,
+				FArgs,
+			) (v string, set bool, err error) {
+				return
+			}, V: map[unique.Handle[Ident]]any{
+				unique.Make(Ident("value")): "\xfd",
+			}},
+		},
+	}}
+	for b.Loop() {
+		if _, _, err := Evaluate[string](s, gcc); err != nil {
+			b.Fatal(err)
+		}
+	}
+}