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+#+TITLE: Aligning columns in Emacs
+#+DATE: 2021-03-26T11:27:34-04:00
+#+DRAFT: false
+#+DESCRIPTION: How to align text separated by whitespace using Emacs
+#+TAGS[]: emacs elisp
+#+KEYWORDS[]: emacs elisp
+#+SLUG:
+#+ALIASES[]: /posts/wip-emacs-align-columns/
+#+SUMMARY:
+
+#+ATTR_HTML: :alt Before and after columns aligned
+#+ATTR_HTML: :title Before and after aligned columns
+[[file:cover.png]]
+
+I've been writing a lot of GraphQL resolvers in ruby at work recently,
+and frequently run into a situation where I have to align many columns
+of text by hand. I figured this isn't a very unique problem, and that
+there was probably already some code within Emacs to handle it.
+
+As it turns out I was correct in my assumption. There's an excellent
+built-in package called =align= that takes care of just that.
+
+Many of the features of the =align= package are mode-specific, but I
+just wanted a function that can align columns regardless of which mode
+they're used in. There's a function that's part of the package that
+can be used for just that fortunately, =align-regexp=, which takes a
+regular expression as input and uses it to guide the alignment.
+
+I was able to use it to make a generic function.
+
+#+begin_src elisp
+(defun align-non-space (BEG END)
+  "Align non-space columns in region BEG END."
+  (interactive "r")
+  (align-regexp BEG END "\\(\\s-*\\)\\S-+" 1 1 t))
+#+end_src
+
+Let's walk through what's going on here.
+
+- =BEG= and =END= are the beginning and end positions of the area to be aligned
+- =(interactive "r")= tells Emacs that the function is interactive,
+  meaning that it can be called from the =M-x= menu
+  - ="r"= tells Emacs that when the function is called interactively, it expects a
+    region (beginning and end points) as arguments
+- =align-regexp= where the work is happening. This function has the
+  following signature.
+  #+begin_src elisp
+  (align-regexp BEG END REGEXP &optional GROUP SPACING REPEAT)
+  #+end_src
+
+  - =BEG= and =END= is the region that it expects as the first arguments
+  - ="\\(\\s-*\\)\\S-+"= is an Emacs regular expression. Backslashes
+    are doubled because they need to be escaped in a string literal
+    - =\( \)= is a capture group
+      - =\s-= is a [[https://www.gnu.org/software/emacs/manual/html_node/elisp/Regexp-Backslash.html][regular expression construct]] specific to Emacs which
+        specifies a type of /syntax/ which is to be matched.
+        - =-= refers to the [[https://www.gnu.org/software/emacs/manual/html_node/elisp/Syntax-Class-Table.html][whitespace characters]]
+      - =*= means match zero or more
+    - =\S-= is similar to the previous construct, but instead means to
+      match anything /other/ than whitespace
+    - =+= means one or more
+  - =1= here refers to the group within the regex that will be
+    modified to align the fields
+  - =1= is the number of spaces between fields once aligned
+  - =t= indicates to repeat the rule multiple times on the same line
+
+To use this function, simply highlight a region you want to align and
+run =M-x align-non-space=.