backquote and scope.

[RyanBurnside]

Good Afternoon,

I'm wondering about the ` semantics in Medley.
I've been using it to construct some lambda functions that contain references.

My question is this, what scope do functions created with it have?
For example, let's say I have a record FOO defined in the system and I construct a function to be passed around that acts on FOO-INSTANCE.

`(lambda () (frobulate ,FOO-INSTANCE ))

That appears to turn into a List of
(LAMBDA () (FROBULATE <instance>))

I've used this for my recent project and it seems be be working really well.
Is it a Common Lisp style lambda or is it a Interlisp style lambda that gets created?
I didn't see a reference to the ` in "online" IRM so I'm not sure which language and scope it's using.

Sorry to beat a dead horse around closures.
I use them very heavily normally ...

Sincerely,
Ryan

[MattHeffron]

For IRM backquote documentation, you can MAN BQUOTE to get the entry in DInfo, or search for backquote in the IRM

As for which LAMBDA is used, that's not something that's determined by backquote processing, it was determined when the form was read.

The ` readmacro, just expands as the form wrapped in IL:BQUOTE, with the , , ,@ , etc. converted to a slightly different IL: litatom.
I.e., your example, entered into the XCL-EXEC:

(QUOTE `(lambda () (frobulate ,FOO-INSTANCE )))

expands to:

(IL:BQUOTE (LAMBDA NIL (FROBULATE (IL:\\\, FOO-INSTANCE))))

(In an Interlisp EXEC, the IL:\\\, is just \,. The extra \ are just for XCL readtable special character quoting in the litatom's p-name.)

That ultimately expands to the code to construct the appropriate form:

(LIST 'LAMBDA NIL (LIST 'FROBULATE FOO-INSTANCE))

The scope is determined as if the code to construct had been manually entered in the surrounding code.

[RyanBurnside]

Ah OK, thanks @MattHeffron .

I was looking for it in the Function Evaluation part of the IRM where QUOTE and friends are listed, I see it's in the Read Macro section.

[masinter]

IL:LAMBDA is an Interlisp-style LAMBDA -- arguments are NIL, a single symbol, a list of symbols. CL:LAMBDA also implies that evaluation follows CL:EVAL while IL:LAMBDA follows IL:EVAL. (I think!)

CL:LAMBDA is common lisp style, with &KEY, &ALLOW-OTHER-KEYS, &OPTIONAL keywords, default values.

IL:LAMBDA can be translated into CL:LAMBDA by

• NIL => (&rest unused) (declare (ignore unused)) ...
• (A B C) => (&optional A B C &rest ignore)
  Interlisp treats all parameters as optional and additional parameters supplied as ignorable.
• single atom N => ... left as exercise.