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+;;; reason-interaction.el --- Phrase navitagion for rtop -*-lexical-binding: t-*-
+
+;; Portions Copyright (c) 2015-present, Facebook, Inc. All rights reserved.
+
+;;; Commentary:
+
+;; Phrase navigation for utop and maybe other REPLs.
+
+;; The utop compatibility layer for Reason was mainly taken from:
+;; https://github.com/ocaml/tuareg/blob/master/tuareg-light.el (big thanks!)
+
+;;; Code:
+
+(defun reason-backward-char (&optional step)
+  "Go back one char.
+Similar to `backward-char` but it does not signal errors
+`beginning-of-buffer` and `end-of-buffer`.  It optionally takes a
+STEP parameter for jumping back more than one character."
+  (when step (goto-char (- (point) step))
+        (goto-char (1- (point)))))
+
+(defun reason-forward-char (&optional step)
+  "Go forward one char.
+Similar to `forward-char` but it does not signal errors
+`beginning-of-buffer` and `end-of-buffer`.  It optionally takes a
+STEP parameter for jumping back more than one character."
+  (when step (goto-char (+ (point) step))
+    (goto-char (1+ (point)))))
+
+(defun reason-in-literal-p ()
+  "Return non-nil if point is inside an Reason literal."
+  (nth 3 (syntax-ppss)))
+
+(defconst reason-comment-delimiter-regexp "\\*/\\|/\\*"
+  "Regex for identify either open or close comment delimiters.")
+
+(defun reason-in-between-comment-chars-p ()
+  "Return non-nil iff point is in between the comment delimiter chars.
+It returns non-nil if point is between the chars only (*|/ or /|*
+where | is point)."
+  (and (not (bobp)) (not (eobp))
+       (or (and (char-equal ?/ (char-before)) (char-equal ?* (char-after)))
+           (and (char-equal ?* (char-before)) (char-equal ?/ (char-after))))))
+
+(defun reason-looking-at-comment-delimiters-p ()
+  "Return non-nil iff point in between comment delimiters."
+  (looking-at-p reason-comment-delimiter-regexp))
+
+(defun reason-in-between-comment-delimiters-p ()
+  "Return non-nil if inside /* and */."
+  (nth 4 (syntax-ppss)))
+
+(defun reason-in-comment-p ()
+  "Return non-nil iff point is inside or right before a comment."
+  (or (reason-in-between-comment-delimiters-p)
+      (reason-in-between-comment-chars-p)
+      (reason-looking-at-comment-delimiters-p)))
+
+(defun reason-beginning-of-literal-or-comment ()
+  "Skip to the beginning of the current literal or comment (or buffer)."
+  (interactive)
+  (goto-char (or (nth 8 (syntax-ppss)) (point))))
+
+(defun reason-inside-block-scope-p ()
+  "Skip to the beginning of the current literal or comment (or buffer)."
+  (and (> (nth 0 (syntax-ppss)) 0)
+       (let ((delim-start (nth 1 (syntax-ppss))))
+         (save-excursion
+           (goto-char delim-start)
+           (char-equal ?{ (following-char))))))
+
+(defun reason-at-phrase-break-p ()
+  "Is the underlying `;' a phrase break?"
+  ;; Difference from OCaml, the phrase separator is a single semi-colon
+  (and (not (eobp))
+       (char-equal ?\; (following-char))))
+
+(defun reason-skip-to-close-delimiter (&optional limit)
+  "Skip to the end of a Reason block.
+It basically calls `re-search-forward` in order to go to any
+closing delimiter, not concerning itself with balancing of any
+sort.  Client code needs to check that.
+LIMIT is passed to `re-search-forward` directly."
+  (re-search-forward "\\s)" limit 'move))
+
+(defun reason-skip-back-to-open-delimiter (&optional limit)
+  "Skip to the beginning of a Reason block backwards.
+It basically calls `re-search-backward` in order to go to any
+opening delimiter, not concerning itself with balancing of any
+sort.  Client code needs to check that.
+LIMIT is passed to `re-search-backward` directly."
+  (re-search-backward "\\s(" limit 'move))
+
+(defun reason-find-phrase-end ()
+  "Skip to the end of a phrase."
+  (while (and (not (eobp))
+              (not (reason-at-phrase-break-p)))
+    (if (re-search-forward ";" nil 'move)
+        (progn (when (reason-inside-block-scope-p)
+                 (reason-skip-to-close-delimiter))
+               (goto-char (1- (point))))
+      ;; avoid infinite loop at the end of the buffer
+      (re-search-forward "[[:space:]\\|\n]+" nil 'move)))
+  (min (goto-char (1+ (point))) (point-max)))
+
+(defun reason-skip-blank-and-comments ()
+  "Skip blank spaces and comments."
+  (cond
+   ((eobp) (point))
+   ((or (reason-in-between-comment-chars-p)
+        (reason-looking-at-comment-delimiters-p)) (progn
+                                                    (reason-forward-char 1)
+                                                    (reason-skip-blank-and-comments)))
+   ((reason-in-between-comment-delimiters-p) (progn
+                                               (search-forward "*/" nil t)
+                                               (reason-skip-blank-and-comments)))
+   ((eolp) (progn
+             (reason-forward-char 1)
+             (reason-skip-blank-and-comments)))
+   (t (progn (skip-syntax-forward " ")
+             (point)))))
+
+(defun reason-skip-back-blank-and-comments ()
+  "Skip blank spaces and comments backwards."
+  (cond
+   ((bobp) (point))
+   ((looking-back reason-comment-delimiter-regexp) (progn
+                                                     (reason-backward-char 1)
+                                                     (reason-skip-back-blank-and-comments)))
+   ((reason-in-between-comment-delimiters-p) (progn
+                                               (search-backward "/*" nil t)
+                                               (reason-backward-char 1)
+                                               (reason-skip-back-blank-and-comments)))
+   ((or (reason-in-between-comment-chars-p)
+        (reason-looking-at-comment-delimiters-p)) (progn
+                                                    (reason-backward-char 1)
+                                                    (reason-skip-back-blank-and-comments)))
+   ((bolp) (progn
+             (reason-backward-char 1)
+             (reason-skip-back-blank-and-comments)))
+   (t (progn (skip-syntax-backward " ")
+             (point)))))
+
+(defun reason-ro (&rest words)
+  "Build a regex matching iff at least a word in WORDS is present."
+  (concat "\\<" (regexp-opt words t) "\\>"))
+
+(defconst reason-find-phrase-beginning-regexp
+  (concat (reason-ro "end" "type" "module" "sig" "struct" "class"
+                     "exception" "open" "let")
+          "\\|^#[ \t]*[a-z][_a-z]*\\>\\|;"))
+
+(defun reason-at-phrase-start-p ()
+  "Return t if is looking at the beginning of a phrase.
+A phrase starts when a toplevel keyword is at the beginning of a line."
+  (or (looking-at "#")
+      (looking-at reason-find-phrase-beginning-regexp)))
+
+(defun reason-find-phrase-beginning-backward ()
+  "Find the beginning of a phrase and return point.
+It scans code backwards, therefore the caller can assume that the
+beginning of the phrase (if found) is always before the starting
+point.  No error is signalled and (point-min) is returned when a
+phrease cannot be found."
+  (beginning-of-line)
+  (while (and (not (bobp)) (not (reason-at-phrase-start-p)))
+    (if (reason-inside-block-scope-p)
+        (reason-skip-back-to-open-delimiter)
+      (re-search-backward reason-find-phrase-beginning-regexp nil 'move)))
+  (point))
+
+(defun reason-discover-phrase ()
+  "Discover a Reason phrase in the buffer."
+  ;; TODO reason-with-internal-syntax ;; tuareg2 modifies the syntax table (removed for now)
+  ;; TODO stop-at-and feature for phrase detection (do we need it?)
+  ;; TODO tuareg2 has some custom logic for module and class (do we need it?)
+  (save-excursion
+    (let ((case-fold-search nil))
+      (reason-skip-blank-and-comments)
+      (list (reason-find-phrase-beginning-backward) ;; beginning
+            (reason-find-phrase-end)                ;; end
+            (save-excursion                         ;; end-with-comment
+              (reason-skip-blank-and-comments)
+              (point))))))
+
+(defun reason-discover-phrase-debug ()
+  "Discover a Reason phrase in the buffer (debug mode)."
+  (let ((triple (reason-discover-phrase)))
+    (message (concat "Evaluating: \"" (reason-fetch-phrase triple) "\""))
+    triple))
+
+(defun reason-fetch-phrase (triple)
+  "Fetch the phrase text given a TRIPLE."
+  (let* ((start (nth 0 triple))
+         (end (nth 1 triple))) ;; we don't need end-with-comment
+    (buffer-substring-no-properties start end)))
+
+(defun reason-next-phrase ()
+  "Skip to the beginning of the next phrase."
+  (cond
+   ((reason-at-phrase-start-p) (point))
+   ((eolp) (progn
+             (forward-char 1)
+             (reason-skip-blank-and-comments)
+             (reason-next-phrase)))
+   ((reason-inside-block-scope-p) (progn (reason-skip-to-close-delimiter)
+                                         (reason-next-phrase)))
+   ((looking-at ";") (progn
+                       (forward-char 1)
+                       (reason-next-phrase)))
+   (t (progn (end-of-line)
+             (reason-next-phrase)))))
+
+(provide 'reason-interaction)
+
+;;; reason-interaction.el ends here