Add example of installation on Doomemacs and fix the stringp nil in error handling

README.org

@@ -1,5 +1,5 @@
 * ob-pasp
-Org-Babel mode to execute Clingo Potassco code within Org-mode
+Org-Babel mode to execute Potassco Answer Set Programming code within Org-mode with =clingo=.
 
 #+begin_src pasp
 child(C, P) :- parent(P, C).
@@ -21,3 +21,25 @@ Calls        : 1
 Time         : 0.000s (Solving: 0.00s 1st Model: 0.00s Unsat: 0.00s)
 CPU Time     : 0.000s
 #+end_example
+
+** Installation
+
+The package is not (yet) available on MELPA, so the package should be installed from github directly.
+
+*** Dependencies
+
+To be able to use =ob-pasp= you will need to install =clingo= cli.
+
+
+*** Doomemacs
+
+In your =$DOOMDIR/package.el= file, you might want to set up the following:
+#+begin_src emacs-lisp
+(package! pasp-mode)    ;; Add syntax highlighting for Potassco ASP
+(package! ob-pasp
+  :recipe (:host github :repo "UncleSamulus/ob-pasp"))
+#+end_src
+
+
+** TODO Spacemacs
+** TODO =use-package= / =straight=

ob-pasp.el

@@ -138,7 +138,7 @@ This function is called by `org-babel-execute-src-block'"
          (vars (org-babel--get-vars processed-params))
          (result-params (assq :result-params processed-params))
          ;; either OUTPUT or VALUE which should behave as described above
-         (result-type (assq :result-type processed-params))
+         (result-type "output"); (assq :result-type processed-params))
          ;; expand the body with `org-babel-expand-body:pasp'
          (full-body (org-babel-expand-body:pasp
                      body params processed-params))
@@ -146,7 +146,7 @@ This function is called by `org-babel-execute-src-block'"
          (clingo (executable-find "clingo"))
          (cmd (concat (shell-quote-argument (expand-file-name clingo))
                       (when models
-                        (concat " -n " models))
+                        (concat " -n " (int-to-string models)))
                       " " (org-babel-process-file-name temp-file))))
     ;; actually execute the source-code block either in a session or
     ;; possibly by dropping it to a temporary file and evaluating the
@@ -165,7 +165,7 @@ This function is called by `org-babel-execute-src-block'"
 
     ;; ref. https://github.com/arnm/ob-mermaid
     (unless (file-executable-p clingo)
-      (error "Cannot find or execute %s, please check `clingo`" clingo))
+      (error "Cannot find or execute `clingo', please check it is installed and in PATH"))
     (with-temp-file temp-file (insert full-body))
     (message "%s" cmd)
     (org-babel-eval cmd "")