cl-curlex

Leak *LEXENV* variable which describes current lexical environment into body of a call. Update: do other exotic stuff, which requires access to the current lexical environment.

Basic example:

CL-USER> (ql:quickload 'cl-curlex)
CL-USER> (cl-curlex:with-current-lexenv *lexenv*)
#S(SB-KERNEL:LEXENV
:FUNS NIL
:VARS NIL
:BLOCKS NIL
:TAGS NIL
:TYPE-RESTRICTIONS NIL
:LAMBDA #<SB-C::CLAMBDA
        :%SOURCE-NAME SB-C::.ANONYMOUS.
        :%DEBUG-NAME (LAMBDA ())
        :KIND NIL
        :TYPE #<SB-KERNEL:FUN-TYPE (FUNCTION NIL (VALUES T &OPTIONAL))>
        :WHERE-FROM :DEFINED
        :VARS NIL {AE26BA9}>
:CLEANUP NIL
:HANDLED-CONDITIONS NIL
:DISABLED-PACKAGE-LOCKS NIL
:%POLICY ((COMPILATION-SPEED . 1) (DEBUG . 1) (INHIBIT-WARNINGS . 1)
          (SAFETY . 1) (SPACE . 1) (SPEED . 1))
:USER-DATA NIL)

Slightly more sophisticated:

CL-USER> (let ((a 1)) (cl-curlex:with-current-lexenv (let ((b 1)) *lexenv*)))
#S(SB-KERNEL:LEXENV
  :FUNS NIL
  :VARS ((A . #<SB-C::LAMBDA-VAR :%SOURCE-NAME A {AEA1371}>))
  :BLOCKS NIL
  :TAGS NIL
  :TYPE-RESTRICTIONS NIL
  :LAMBDA #<SB-C::CLAMBDA
          :%SOURCE-NAME SB-C::.ANONYMOUS.
          :%DEBUG-NAME (LET ((A 1))
                              )
          :KIND :ZOMBIE
          :TYPE #<SB-KERNEL:BUILT-IN-CLASSOID FUNCTION (read-only)>
          :WHERE-FROM :DEFINED
          :VARS (A) {AEA14B1}>
  :CLEANUP NIL
  :HANDLED-CONDITIONS NIL
  :DISABLED-PACKAGE-LOCKS NIL
  :%POLICY ((COMPILATION-SPEED . 1) (DEBUG . 1) (INHIBIT-WARNINGS . 1)
            (SAFETY . 1) (SPACE . 1) (SPEED . 1))
  :USER-DATA NIL)

Example of use of ABBROLET:

CL-USER> (macrolet ((bar () 123))
           (cl-curlex:abbrolet ((foo bar))
             (foo)))
123

Package exports several macros that do interesting stuff with current lexical environment:

• FART-CURRENT-LEXENV which simply prints current lexenv, but not leaks it into its body,
• WITH-CURRENT-LEXENV, which leaks *LEXENV* variable into its body
• WITH-CURRENT-CC-LEXENV - like WITH-CURRENT-LEXENV, only useful when defining macros. I.e., instead of leaking *LEXENV* into the run-time from compile-time, it makes lexical environment accesible to macros via *LEXENV* at compile-time.
• ABBROLET, which allows to locally function or macro with another name

N.B.: leaking is for reading purposes only, and *LEXENV* captures state of lexical environment as it were on enter to WITH-CURRENT-LEXENV, not as it is when *LEXENV* var is used - this is why in the "sophisticated" example B variable is not seen in *LEXENV* - it was not there, when we entered WITH-CURRENT-LEXENV, it was binded somewhere inside.

N.B.: Although the ultimate goal is to leak lexenv in all major implementations, the form of a *LEXENV* will be (intentionally) implementation specific.

N.B.: Is WITH-CURRENT-CC-LEXENV really necessary? After all, ANSI standard specifies, that one of the arguments to *MACROEXPAND-HOOK* function is lexical environment, in which macro is expanded. However, what it does not specify, is a way for a macro to actually access that variable, when macro is defined using DEFMACRO. And in fact, SBCL safely gensyms this variable away. So, the one, who wishes to access *LEXENV* in macros has 2 choices:

• Roll his own implementation of DEFMACRO, which leaks *LEXENV* to all macros. This is implementation-dependent.
• Write something like WITH-CURRENT-CC-LEXENV, which in principle allows to access *LEXENV* inside macro-definition, but this is not the default for all macro. This is also implementation-dependent. I decided to go second way, since it requires far less code and is, in my opinion, cleaner.

Main use-case for ABBROLET is to locallly INTERN some function or macro from one package to another, see e.g. my CL-LARVAL project to see, how it's used to define DSL locally.

    CL-USER> (abbrolet ((name1 other-package::name2))
               (name1 a b c))

TODO:

• support major CL implementations for *-current-lexenv macros
  • SBCL
    • lexenv capture is not full, only names of functions, variables and so on are captured, advanced features like package locks and policies are not captured
  • (wont, don't have an access to sources or other spec of non-standard features) Allegro
  • CLISP
    • there is no centralized concept of lexical environment - dont know, what to do
    • even if there was one - WITHOUT-PACKAGE-LOCKS does not seem to work right - it converts every symbol to T, thus rendering patching of compiler impossible.
  • CMUCL
    • same as SBCL, only names of variables, functions and so on are captured.
  • ECL
    • actual values of variables, functions etc are also stripped
    • I also removed :DECLARE's and 'LBs, since I don't know how to handle them smartly
    • WITH-CURRENT-LEXENV and FART-CURRENT-LEXENV work only when compiled, not from the Slime's REPL. Although compiled function can, of course, be invoked from the REPL, with the desired results.
  • LispWorks - probably won't have the sources either
  • OpenMCL (Clozure CL)
    • only variables and functions are captured
• support major CL implementations for ABBROLET
  • SBCL done
  • CMUCL done
  • ECL - everything, except abbroletting global functions, done
  • CCL - everything, except abbroletting global functions, done