[O] input data for babel blocks

[Alan Schmitt]

Hello,

In my quest for analyzing my data in org mode tables, I'm trying to see
if I can use my favorite language (i.e., ocaml). I'm thus looking at how
to input such tables in a caml program. I found that the following works
well:

--8<---------------cut here---------------start------------->8---
#+name: data
| 12 |
| 42 |

#+BEGIN_SRC ocaml :var x=data
x
#+END_SRC

#+RESULTS:
: - : int array array = [|[|12|]; [|42|]|]
--8<---------------cut here---------------end--------------->8---

(The only "bad" thing is that a single value is an array, but this is
probably related to the following thing.) Unfortunately (for interaction
with org mode), caml is strongly typed, and arrays must be
homogeneous. Thus the following fails:

--8<---------------cut here---------------start------------->8---
#+name: myinput
| x | 12 |
| y | 24 |

#+BEGIN_SRC ocaml :var x=myinput
x
#+END_SRC
--8<---------------cut here---------------end--------------->8---

with the error in the toplevel:

--8<---------------cut here---------------start------------->8---
# let x = [|[|"x"; 12|]; [|"y"; 24|]|];;
x;;
"org-babel-ocaml-eoe";;
Characters 17-19:
  let x = [|[|"x"; 12|]; [|"y"; 24|]|];;
                   ^^
Error: This expression has type int but an expression was expected of type
         string
--8<---------------cut here---------------end--------------->8---

I would like to change the parsing of table in ob-ocaml so that it
generates an array of _tuples_, for instance for the previous example:

#+BEGIN_SRC ocaml
let x = [| ("x", 12); ("y", 24) |];;
#+END_SRC

I looked at the code, and this seems to be the relevant part:

#+BEGIN_SRC emacs-lisp
(defun org-babel-variable-assignments:ocaml (params)
  "Return list of ocaml statements assigning the block's variables."
  (mapcar
   (lambda (pair) (format "let %s = %s;;" (car pair)
                          (org-babel-ocaml-elisp-to-ocaml (cdr pair))))
   (mapcar #'cdr (org-babel-get-header params :var))))

(defun org-babel-ocaml-elisp-to-ocaml (val)
  "Return a string of ocaml code which evaluates to VAL."
  (if (listp val)
      (concat "[|" (mapconcat #'org-babel-ocaml-elisp-to-ocaml val "; ") "|]")
    (format "%S" val)))
#+END_SRC

I tried tweaking this to the following:

#+BEGIN_SRC emacs-lisp
(defun org-babel-variable-assignments:ocaml (params)
  "Return list of ocaml statements assigning the block's variables."
  (mapcar
   (lambda (pair) (format "let %s = %s;;" (car pair)
                          (org-babel-ocaml-elisp-to-ocaml (cdr pair))))
   (mapcar #'cdr (org-babel-get-header params :var))))

(defun org-babel-ocaml-elisp-to-ocaml (val)
  "Return a string of ocaml code which evaluates to VAL."
  (if (listp val)
      (concat "[|" (mapconcat #'org-babel-ocaml-elisp-to-ocaml-tuple val "; ") 
"|]")
    (format "%S" val)))

(defun org-babel-ocaml-elisp-to-ocaml-tuple (val)
  "Return a string of ocaml code which evaluates to VAL, as a tuple."
  (if (listp val)
      (concat "(" (mapconcat #'org-babel-ocaml-elisp-to-ocaml-tuple val ", ") 
")")
    (format "%S" val)))
#+END_SRC

Now the example seems to work:

--8<---------------cut here---------------start------------->8---
#+name: myinput
| x | 12 |
| y | 24 |

#+BEGIN_SRC ocaml :var x=myinput
x
#+END_SRC

#+RESULTS:
: - : (string * int) array = [|("x", 12); ("y", 24)|]
--8<---------------cut here---------------end--------------->8---

(and the previous example is even nicer:
--8<---------------cut here---------------start------------->8---
#+name: data
| 12 |
| 42 |

#+BEGIN_SRC ocaml :var x=data
x
#+END_SRC

#+RESULTS:
: - : int array = [|12; 42|]
--8<---------------cut here---------------end--------------->8---
)

I have the following questions for the list:
- can I always assume that tables are passed as lists of lists?
- would the patch above be a useful way to deal with this?
- is there a way to specify the :var parsing in a code block or in the table?

Thanks,

Alan