feat: fmt.Stringer

pkg/expr/expr.go

@@ -2,10 +2,14 @@
 // expression types in the lambda interpreter.
 package expr
 
+import (
+	"fmt"
+)
+
 // Expression is the base interface for all evaluatable expression types.
 // Different evaluation modes (lambda calculus, SKI combinators, typed lambda
 // calculus, etc.) implement this interface with their own concrete types.
 type Expression interface {
-	// String returns a human-readable representation of the expression.
-	String() string
+	// The expression should have a human-readable representation.
+	fmt.Stringer
 }