Request for comments (this includes stylistic / spelling corrections) -T. Status: Draft Forum: Common Lisp Document Repository (CDR) Issue: INSPECTOR-HOOK References: INSPECT (function), *DEBUGGER-HOOK* (variable) Category: Addition Edit History: 20-Mar-2008 by Rittweiler (Draft) Problem Description: Cross-implementation Lisp programming environments such as SLIME or Climacs face the problem that the ANSI Common Lisp standard does not specify any way to hook into the inspection machinery of an implementation. Specifically, there is no portable way to install an inspector that is run when the function INSPECT is invoked. Proposal (INSPECTOR-HOOK:*INSPECTOR-HOOK*-VARIABLE) Add a variable: *INSPECTOR-HOOK* [VARIABLE] Value Type: A designator for a function of one argument (the object to be inspected), or NIL. Initial Value: NIL. Description: When the value of *INSPECTOR-HOOK* is non-NIL, an invocation of INSPECT in the dynamic-extent of this variable results in calling the value with the object that was originally passed to INSPECT. *INSPECTOR-HOOK* is not rebound before calling the function denoted by the value, i.e. it's bound to the same value as at the invocation of INSPECT; this is to allow inspectors to be defined recursively. The return value of INSPECT is independent of the return value of the denoted function, and remains implementation-dependent. Affected By: INSPECT See Also: *DEBUGGER-HOOK* Notes: It's possible to invoke the implementation's inspection machinery from within *INSPECTOR-HOOK* by binding it to NIL before invoking INSPECT. Rationale: This proposal was closely modelled on the specification of *DEBUGGER-HOOK*, and allows programs to install their own inspectors that are adapted to their respective domains. Notes: The proposal does deliberately say nothing about the home-package of the symbol *INSPECTOR-HOOK*. However, implementors are encouraged to export this symbol from their extensions package (often called "EXT") or another appropriate package---unless a later CDR document specifies a more explicit location. Current Practise: On at least SBCL, Clisp, and Clozure CL, it's possible to straightforwardly hook into their inspection machinery, albeit by mostly unexported and undocumented means. The documentation of Franz' Allegro CL states that an invocation of INSPECT runs a GUI inspector on the MS Windows operating system, and a text-based inspector on other operating systems, so it's very likely that they employ some hook mechanism internally. Cost to implementators: Negligible. Cost to user: None. The proposal is fully upward compatible. Cost of Non-Adoption: The problem, as described above, remains. Benefits: Slightly more powerful / convenient Lisp programming environments. Aesthetics: Inhibits the necessity to rely on implementation-dependent cruft.