From b4ac0fa66a3212fad3373a68d84d4b74c5fd309c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Mon, 18 Mar 2019 21:57:47 +0100
Subject: Wrote a bunch of documentation.

---
 monad/optional.scm | 10 +++++++++-
 monad/stack.scm    | 13 +++++++------
 monad/state.scm    | 33 +++++++++++++++++++--------------
 3 files changed, 35 insertions(+), 21 deletions(-)

(limited to 'monad')

diff --git a/monad/optional.scm b/monad/optional.scm
index 015fc90..06c0e67 100644
--- a/monad/optional.scm
+++ b/monad/optional.scm
@@ -1,3 +1,10 @@
+;;; Commentary:
+;;
+;; Your classical optional (Maybe) monad.
+;; It has the constructors @code{just} and @code{nothing}.
+;;
+;;; Code:
+
 (define-module (monad optional)
   #:use-module (oop goops)
   #:use-module (ice-9 match)
@@ -34,7 +41,8 @@ the value embedded in maybe-val"
       default))
 
 (define ((wrap-maybe proc) . values)
-  "Wraps a function in an optional monad, where #f returns are translated to nothing."
+  "Wraps a function in an optional monad, where #f returns are translated to
+nothing."
   (let ((v (apply proc values)))
     (if v (just v) (nothing))))
 
diff --git a/monad/stack.scm b/monad/stack.scm
index 8d25303..fee48a6 100644
--- a/monad/stack.scm
+++ b/monad/stack.scm
@@ -1,14 +1,15 @@
+;;; Commentary:
+;; Simple stateful stack module for showing the state monad
+;; in action. These functions assume that they are in a
+;; (state list) monad. But dynamic types!
+;;
+;; TODO test these for empty stack
+;;; Code:
 (define-module (monad stack)
   #:export (pop peek push)
   #:use-module (monad)
   #:use-module (monad state))
 
-;;; Simple stateful stack module for showing the state monad
-;;; in action. These functions assume that they are in a
-;;; (state list) monad. But dynamic types!
-
-;;; TODO test these for empty stack
-
 (define (pop)
   (do st <- (get)
       let top = (car st)
diff --git a/monad/state.scm b/monad/state.scm
index 471e756..40c9ff5 100644
--- a/monad/state.scm
+++ b/monad/state.scm
@@ -1,13 +1,26 @@
+;;; Commentary:
+;;
+;; The state monad!
+;; State is best modelled monadically as a function taking a state object, and
+;; returning another state object. This state object is in turn represented as i
+;; list where the first value is the last value returned, and the secound value
+;; is the internal state.
+;;
+;; All access to this internal value is done through the methods @code{get},
+;; @code{put}, and @code{modify}.
+;;
+;; One side effect of the @code{<state>} object not being directly accessible is
+;; that my trick for multiple dispatch return doesn't work. Which is why this
+;; modules also exports @code{return-state} directly.
+;;
+;;; Code:
+
 (define-module (monad state)
   #:use-module (oop goops)
   #:use-module (ice-9 match)
   #:use-module (monad)
   #:export (return-state run-state get put modify)
-  #:re-export (>>= >> fmap return))
-
-
-;; Alternative implementation of get.
-;; See https://hackage.haskell.org/package/mtl-2.2.1/docs/src/Control.Monad.State.Class.html#get
+  #:re-export (>>= >> return))
 
 ;;; newtype State = st-list -> st-list
 
@@ -48,10 +61,6 @@
       ((v _)
        ((proc (f v)) new-st-list)))))
 
-;; (define-stateful-method ((>> (a <state>) (b <state>)) st-list-a)
-;;   (let ((st-list-b ((proc a) st-list-a)))
-;;     ((proc b) st-list-b)))
-
 (define-stateful ((return-state v) st-list)
   "Sets the return value to v"
   (cons v (cdr st-list)))
@@ -69,15 +78,11 @@
   (list '() v))
 
 (define-stateful ((modify proc) st-list)
+  "Applies proc to the value stored in state, and stores it back"
   (match st-list
     ((r s)
      (list '() (proc s)))))
 
-;; (define-stateful-method ((fmap (f <procedure>) (s <state>)) st-list)
-;;   (match ((proc s) st-list)
-;;     ((r st)
-;;      (list (f r) st))))
-
 (define-method (run-state (st <state>) init)
   "Exec state with init as starting state value and st."
   ((proc st) (list init init)))
-- 
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