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+;; Visualise the internal structure of an Emacs Lisp file using
+;; Graphviz.
+;;
+;; Entry point is the function `edeps-analyse-file'.
+
+(require 'map)
+
+(defun edeps-read-defs (file-name)
+  "Stupidly read all definitions from an Emacs Lisp file. This only
+considers top-level forms, where the first element of the form is
+a symbol whose name contains the string `def', and where the
+second element is a symbol.
+
+Returns a hashmap of all these symbols with the remaining forms
+in their bodies."
+
+  (with-temp-buffer
+    (insert-file-contents file-name)
+    (goto-char (point-min))
+
+    (let ((symbols (make-hash-table)))
+      (condition-case _err
+          (while t
+            (let ((form (read (current-buffer))))
+              (when (and (listp form)
+                         (symbolp (car form))
+                         (string-match "def" (symbol-name (car form)))
+                         (symbolp (cadr form)))
+                (when (and (map-contains-key symbols (cadr form))
+                           ;; generic methods have multiple definitions
+                           (not (eq (car form) 'cl-defmethod)))
+                  (error "Duplicate symbol: %s" (symbol-name (cadr form))))
+
+                (map-put! symbols (cadr form)
+                          (cons (car form) (cddr form))))))
+        (end-of-file symbols)))))
+
+(defun edeps-analyse-structure (symbols)
+  "Analyse the internal structure of the symbols found by
+edeps-read-defs, and return a hashmap with the results of the
+analysis. The hashmap uses the symbols as keys, "
+  (let ((deps (make-hash-table)))
+    (map-do
+     (lambda (sym val)
+       (dolist (expr (flatten-list (cdr val)))
+         (when (map-contains-key symbols expr)
+           (map-put! deps expr (cons sym (ht-get deps expr))))))
+     symbols)
+    deps))
+
+(defun edeps-graph-deps (symbols deps)
+  (with-temp-buffer
+    (insert "digraph edeps {\n")
+
+    ;; List all symbols first
+    (insert "  subgraph {\n")
+    (map-do
+     (lambda (sym val)
+       (insert "    " (format "\"%s\" [label=\"%s\\n(%s)\"];\n" sym sym (car val))))
+     symbols)
+    (insert "  }\n\n")
+
+    ;; Then drop all the edges in there ..
+    (insert "  subgraph {\n")
+    (map-do
+     (lambda (sym deps)
+       (dolist (dep deps)
+         (insert "    " (format "\"%s\" -> \"%s\";\n" dep sym))))
+     deps)
+    (insert "  }\n")
+
+    (insert "}\n")
+    (buffer-string)))
+
+(defun edeps-analyse-file (infile outfile)
+  "Produces a dot-graph in OUTFILE from an internal structural
+analysis of INFILE. This can be graphed using the graphviz
+package."
+  (let* ((symbols (edeps-read-defs infile))
+         (deps (edeps-analyse-structure symbols)))
+    (with-temp-buffer
+      (insert (edeps-graph-deps symbols deps))
+      (write-file outfile))))