Add scheme module README

The README.org has the prereqs as well as links to geiser and the
various scheme implementations.

init.example.el

@@ -141,6 +141,7 @@
        ;;ruby              ; 1.step {|i| p "Ruby is #{i.even? ? 'love' : 'life'}"}
        ;;rust              ; Fe2O3.unwrap().unwrap().unwrap().unwrap()
        ;;scala             ; java, but good
+       ;;scheme            ; a fully conniving family of lisps
        sh                ; she sells {ba,z,fi}sh shells on the C xor
        ;;solidity          ; do you need a blockchain? No.
        ;;swift             ; who asked for emoji variables?

modules/lang/scheme/README.org

@@ -0,0 +1,38 @@
+#+TITLE:   lang/scheme
+#+DATE:    July 23, 2019
+#+SINCE:   {replace with next tagged release version}
+#+STARTUP: inlineimages
+
+* Table of Contents :TOC_3:noexport:
+- [[#description][Description]]
+  - [[#module-flags][Module Flags]]
+- [[#prerequisites][Prerequisites]]
+- [[#features][Features]]
+  - [[#commands][Commands]]
+    - [[#geiser][Geiser]]
+
+* Description
+This module provides an environment for hacking and having fun in scheme. It is
+powered by [[https://www.nongnu.org/geiser/geiser_1.html#introduction][geiser]].
+
+** Module Flags
+This module provides no flags.
+
+
+* Prerequisites
+This module requires you to have at least one of the supported schemes, namely:
+- [[https://www.gnu.org/software/guile][Guile]] 2.2.0 or better
+- [[https://call-cc.org][Chicken]] 4.8.0 or better
+- [[https://www.gnu.org/software/mit-scheme][MIT/GNU Scheme]] 9.1.1 or better
+- [[https://synthcode.com/scheme/chibi][Chibi Scheme]] 0.7.3 or better
+- [[https://www.scheme.com][Chez Scheme]] 9.4 or better
+
+Their executables must be present in your path for geiser to work properly.
+
+* Features
+** Commands
+*** Geiser
+| command             | key / ex command | description          |
+|---------------------+------------------+----------------------|
+| ~+scheme/open-repl~ | =:repl=          | Open the Scheme Repl |
+|                     |                  |                      |

modules/lang/scheme/config.el

@@ -2,20 +2,12 @@
 
 (add-hook 'scheme-mode-hook #'rainbow-delimiters-mode)
 
-(defun +scheme/impls ()
-  `( ,@(when (featurep! +racket)  '(racket))
-     ,@(when (featurep! +guile)   '(guile))
-     ,@(when (featurep! +chicken) '(chicken))
-     ,@(when (featurep! +mit)     '(mit))
-     ,@(when (featurep! +chibi)   '(chibi))
-     ,@(when (featurep! +chez)    '(chez)) ()))
-
 (def-package! geiser
   :mode ("\\.scm\\'" . scheme-mode)
   :mode ("\\.ss\\'"  . scheme-mode)
   :commands (geiser)
   :init
-  (setq geiser-active-implementations #'+scheme/impls)
+  (setq geiser-active-implementations '(guile chicken mit chibi chez))
   (set-repl-handler! 'scheme-mode '+scheme/repl)
   (set-eval-handler! 'scheme-mode #'geiser-eval-region)
   (set-lookup-handlers! 'scheme-mode
@@ -36,7 +28,8 @@
               "R" #'geiser-eval-region-and-go)
 
             (:prefix ("h" . "help")
-              "d" 'geiser-autodoc)
+              "d" 'geiser-autodoc
+              ;; TODO add more help keybindings)
 
             (:prefix ("r" . "repl")
               "b" #'geiser-switch-to-repl