executing scheme in org-mode babel

Question

I want to write a scheme program in an org file. I want to be able to execute the #+SRC blcoks and see the result in #+RESULT: block. However, when I execute the #+SRC_BEGIN/END I get no output. Instead I get a guile REPL and that's it.

These are the config I have:

(setq geiser-default-implementation 'guile)


(org-babel-do-load-languages
'org-babel-load-languages
'((scheme . t)
 (emacs-lisp . t)
 (ruby . t)
 (R . t)
 (python . t)
 (C . t)
 (sh . t)))

There's an interesting detail. When I execute this code

#+SRC_BEGIN
(write "hello")
#+END_SRC

I get this output in the org file:

#+RESULTS:
[blank here]

And another buffer with this:

=> #<unspecified>


"hello world";; -*- geiser-scheme-implementation: guile -*-
(write "hello world")

But the following program produces no output at all, not even the empty #+RESULT: block, except for a new guile REPL with nothing loaded into it.

This is the program (from SICP):

#+NAME rules
#+BEGIN_SRC scheme :tangle yes :noweb yes
(define (deriv exp var)
  (cond ((constant? exp var) 0 )
        ((same-var? exp var) 1)
        ((sum? exp)
         (make-sum (deriv (A1 exp) var)
                   (deriv (A2 exp) var)))
        ((product? exp) 
         (make-sum (make-product (M1 exp)
                                 (deriv (M2 exp) var))
                   (make-product (deriv (M1 exp) var)
                                 (M2 exp)))))) 
#+END_SRC

#+BEGIN_SRC scheme :tangle yes :noweb yes

(define atom?
  (lambda (x)
    (and (not (pair? x)) (not (null? x)))))


(define (constant? exp var)
  (and (atom? exp)
       (not (eq? exp var))))


(define (same-var? exp var)
  (and (atom? exp)
       (eq? exp var)))


(define (sum? exp)
  (and (not (atom? exp))
       (eq? (car exp) '+)))


(define (make-sum a1 a2)
  (list '+ a1 a2))


(define A1 cadr) ;;TODO rewrite these as lambda expressions (lambada (x) (car (cdr x)). something like that.


(define A2 caddr) 


(define (product? exp)
  (and (not (atom? exp))
       (eq? (car exp) '*)))


(define (make-product m1 m2)
  (list '* m1 m2))


(define M1 cadr)


(define M2 caddr)


(define foo '(+ (* a (* x x))
               (* (* b x)
                  c)))


<<rules>>


(deriv foo 'x)


#+END_SRC

Can someone tell me why the program isnt executed and instead a guile REPL is opened for some reason?

Answer 1

But what I really want, is org-mode to tangle it behind the scenes a print the result of the execution into this file.

For that you need the :results directive as shown below.

BEGIN_SRC scheme :tangle yes :noweb yes :results output

See babel documentation for details of whether to use value instead of output in the :results directive. Value is good if want only the last statement's output.