Can I save source files in Clisp?
I'm a beginner programmer and am going through the book "Land of Lisp".
I have been typing in the examples from the book with the REPL. Is it possible to save my current program as a .lisp file so I can load it and continue working on it later? I know I can just create the .lisp files in a text editor and load them in, but I am enjoying using the REPL in full screen mode to do the examples.
Answer
Short answer
No. Once you enter a function into the REPL, the source form is gone and you just have the interpreted or compiled form. You can do some clever things, but I suspect you don't want to deal with them right now.
Long answer
Use Emacs and SLIME
First, I know you are enjoying the REPL, but I would encourage you to look at some of the editors with Lisp support, such as Emacs with SLIME (http://common-lisp.net/project/slime/) that gives you the best of both worlds. You type into the editor, it types into the REPL, and you really don't know the difference from how you are doing things now. Then you can copy and paste the functions you like into a "proper" .lisp file. The other advantage of using Emacs is that it's based on a variant of Lisp called Elisp, so you can program your editor in Lisp. You can pretty print your code, reformat and refactor it into multiple functions, and do all kinds of excellent things.
Enough preaching!
If you still just want to type clisp and play at the REPL, then you still have options.
If you want to log the output of your REPL session, check out DRIBBLE. It will log your session to a file, and you can edit that later to extract what you want.
For example, this is a simple session:
ataylor:~ $ clisp
blah blah
[1]> (dribble "/Users/ataylor/jerome.lisp")
#<OUTPUT BUFFERED FILE-STREAM CHARACTER #P"/Users/ataylor/jerome.lisp">
[2]> (defun add-two (a b) (+ a b))
ADD-TWO
[3]> (add-two 1 2)
3
[4]> (dribble)
#<CLOSED OUTPUT BUFFERED FILE-STREAM CHARACTER #P"/Users/ataylor/jerome.lisp">
[5]>
Bye.
Viewing the contents of the file is easy, but it can get big quickly.
ataylor:~ $ cat jerome.lisp
;; Dribble of #<IO TERMINAL-STREAM> started on 2011-09-14 18:16:57.
#<OUTPUT BUFFERED FILE-STREAM CHARACTER #P"/Users/ataylor/jerome.lisp">
[2]> (defun add-two (a b) (+ a b))
ADD-TWO
[3]> (add-two 1 2)
3
[4]> (dribble)
;; Dribble of #<IO TERMINAL-STREAM> finished on 2011-09-14 18:17:16.
You could copy (defun add-two (a b) (+ a b)) and paste it into a file for later.
Loading that file (I added it to jerome1.lisp) is very simple.
ataylor:~ $ cat jerome1.lisp
(defun add-two (a b) (+ a b))
ataylor:~ $ clisp
blah blah
[1]> (load "/Users/ataylor/jerome1.lisp")
;; Loading file /Users/ataylor/jerome1.lisp ...
;; Loaded file /Users/ataylor/jerome1.lisp
T
[2]> (add-two 1 2)
3
[3]>
Bye.
Saving a session
The easiest thing you can do is saving your Lisp session to an image. It will save all of the functions you've created or compiled, along with most state. When you load it at your next session, it will be almost as if you hadn't exited clisp. The way to do this is implementation dependent, and differs between clisp, sbcl, etc. I'll show you what you would do for clisp.
The problem with this is that you can't open a file and edit it, post it on github, or whatever. I'll give a brief example.
ataylor:~ $ clisp
blah blah
[1]> (defun add-two (a b) (+ a b))
ADD-TWO
[2]> (add-two 1 2)
3
[3]> (EXT:SAVEINITMEM)
;; Wrote the memory image into lispinit.mem (3,422,616 bytes)
Bytes permanently allocated: 171,840
Bytes currently in use: 3,243,400
Bytes available until next GC: 808,130
3243400 ;
808130 ;
171840 ;
1 ;
65640 ;
7834
[4]>
Bye.
Note that message about where clisp wrote the memory image. You'll give that back to clisp with the -M flag when starting it the next time.
ataylor:~ $ clisp -M lispinit.mem
blah blah
[1]> (add-two 1 2)
3