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by wostusername 2432 days ago
Conditionals are not functions in Lisp. They are 'special forms' since they have to control the evaluation of their arguments and functions always evaluate all their arguments.

So, if you want to translate a lisp into another language you have to resort to macros.

1 comments

None and none, as what you need is to alias the symbols for most lisps.
Been a while since I've done Lisp seriously, but I don't believe that's possible, at least in Common Lisp (SBCL). While if responds to symbol function:

  * (symbol-function 'if)
  #<CLOSURE (:SPECIAL IF) {1000C5084B}>
SBCL refuses to set that value to an alias:

  * (setf (symbol-function 'foo) (symbol-function 'if))
  #<THREAD "main thread" RUNNING {10005205B3}>:
    #<CLOSURE (:SPECIAL IF) {1000C5084B}> is not acceptable to (SETF SYMBOL-FUNCTION)
Trying this with regular functions works as intended:

  * (setf (symbol-function 'bar) (symbol-function 'mapcar))
  #<FUNCTION MAPCAR>
  * (bar #'1+ '(1 2 3))
  (2 3 4)
Special forms are, well, special and a lot of the regular parts of lisp doesn't work with them.
hmm, I think worst case symbol-macro should work there :/

I expected specials to work in this case, but apparently not.

Yes; alias the symbols that are macro operators or special operators via macros, and alias other kinds of symbols in their respective namespaces.

Variables may also have to be done with macros, because you want an assignment to a translated variable name to appear in the original variable. Some Lisp dialects perhaps allow a variable cell to have a binding to two or more symbols which could do the same thing.