Add lcp-mode for Emacs

Reviewers: mtomic, buda

Reviewed By: mtomic

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1549

tools/emacs-lcp/README.md

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+# lcp-mode
+
+Emacs major mode for editing LCP files. It relies on `mmm-mode` for
+integrating multiple major modes in a single buffer.
+
+`lcp-mode` is derived from `lisp-mode`, so all your custom bindings for that
+mode should work out of the box. Since LCP supports embedding C++ code blocks,
+the `lcp-mode` shifts from `lisp-mode` to `c-mode` in such blocks. Therefore,
+your `c-mode` bindings should also work. You may wonder why isn't `c++-mode`
+used. The reason is that, unfortunately, `c++-mode` has some issues when used
+with `mmm-mode`.
+
+Future improvements to this mode may include fixing issues with `c++-mode`,
+adding additional syntax highlighting as well as new editing commands.
+
+## Installation
+
+Just put the following somewhere in your Emacs init file. It will
+automatically install `mmm-mode` from the ELPA repository if needed.
+
+    (require 'lcp-mode "<path-to-memgraph>/tools/emacs-lcp/lcp-mode.el")

tools/emacs-lcp/lcp-mode.el

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+(defun require-package (package &optional min-version no-refresh)
+  "Install PACKAGE with optional MIN-VERSION.
+  If NO-REFRESH is non NIL, the available package list will not be refreshed."
+  (if (package-installed-p package min-version)
+      t
+    (if (or (assoc package package-archive-contents) no-refresh)
+        (package-install package)
+      (package-refresh-contents)
+      (package-install package))))
+
+(require-package 'mmm-mode)
+(require 'mmm-mode)
+
+(setq mmm-global-mode 'maybe)
+
+(define-derived-mode lcp-mode lisp-mode "LCP" "Mode for editing LCP files at Memgraph."
+  (setq mmm-submode-decoration-level 0))
+
+(mmm-add-classes '((lcp-c++ :submode c-mode ; c++-mode is buggy
+                            :front "#>cpp" :back "cpp<#")))
+(mmm-add-mode-ext-class 'lcp-mode nil 'lcp-c++)
+
+(add-to-list 'auto-mode-alist '("\\.lcp\\'" . lcp-mode))
+
+(provide 'lcp-mode)