如何在SBCL中创建解释型函数而非编译型函数？

Great question! The problem with your initial approach is that SBCL treats top-level definitions like defun specially—even when wrapped in a let binding for sb-ext::*evaluator-mode*, the defun itself gets compiled by default, ignoring the binding you set. Here's why and how to fix it:

Why Your Original Code Didn't Work #

When you run:

(let ((sb-ext::*evaluator-mode* :interpret))
  (defun bar (x) (+ x 1)))

SBCL processes the defun as a top-level compilation form before evaluating the let body's runtime environment. The *evaluator-mode* binding only affects code that's evaluated at runtime via eval, not top-level forms that the compiler picks up directly.

Fix 1: Use eval with *evaluator-mode* Binding #

To force the defun to be interpreted, you need to pass its expression to eval—this ensures the *evaluator-mode* setting is respected during evaluation:

(let ((sb-ext::*evaluator-mode* :interpret))
  (eval '(defun bar (x) (+ x 1))))

Now if you check:

CL-USER> (compiled-function-p #'bar)
NIL

This confirms bar is an interpreted function.

Fix 2: Use sb-ext:interpret Directly #

SBCL provides a dedicated function sb-ext:interpret that bypasses the compiler and uses the interpreter for a given expression. This is even cleaner:

(sb-ext:interpret '(defun bar (x) (+ x 1)))

Running (compiled-function-p #'bar) will also return NIL here, since sb-ext:interpret explicitly uses the interpreter regardless of the default *evaluator-mode* setting.

Key Takeaway #

• sb-ext::*evaluator-mode* controls the behavior of the eval function, not top-level forms processed directly by the compiler.
• To create interpreted functions, either wrap the defun form in eval with the mode set to :interpret, or use sb-ext:interpret directly.

内容的提问来源于stack exchange，提问作者Jérôme Radix