diff --git a/cmd/lambda/lambda_engine_list.go b/cmd/lambda/lambda_engine_list.go
index 338098d..c69dbd3 100644
--- a/cmd/lambda/lambda_engine_list.go
+++ b/cmd/lambda/lambda_engine_list.go
@@ -11,7 +11,7 @@ func LambdaEngineList() *cobra.Command {
 		Use:     "list",
 		Aliases: []string{"ls"},
 		Short:   "List available engines",
-		RunE: func(cmd *cobra.Command, args []string) error {
+		RunE: func(*cobra.Command, []string) error {
 			r := GetRegistry()
 
 			for engine := range r.ListEngines() {
diff --git a/pkg/codec/codec.go b/pkg/codec/codec.go
index ecbe258..160547d 100644
--- a/pkg/codec/codec.go
+++ b/pkg/codec/codec.go
@@ -1,8 +1,20 @@
+// Package codec defines processes to convert between different representations
+// of lambda calculus, and serialize the different representations.
 package codec
 
+// A Conversion is a function that turns one representation into another.
+// Returns an error if the input expression cannot be converted.
 type Conversion[T, U any] = func(T) (U, error)
 
+// A Codec is an object that can serialize/deserialize one type of
+// representation. It is assumed that for any x ∋ T, Decode(Encode(x)) = x.
 type Codec[T any] interface {
+	// Encode takes an expression, and returns its serialized format, as a
+	// string. Returns an error if the expression cannot be serialized.
 	Encode(T) (string, error)
+
+	// Decode takes the serialized format of an expression, and returns its true
+	// value. Returns an error if the string doesn't correctly represent any
+	// valid expression.
 	Decode(string) (T, error)
 }
diff --git a/pkg/lambda/expression.go b/pkg/lambda/lambda.go
similarity index 100%
rename from pkg/lambda/expression.go
rename to pkg/lambda/lambda.go