From 3bb58fdc2854aa52826fd1d5f8786c0151518672 Mon Sep 17 00:00:00 2001
From: tomsmeding <tom.smeding@gmail.com>
Date: Sun, 10 Mar 2019 19:51:18 +0100
Subject: Add 'help'

---
 src/Main.hs | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/src/Main.hs b/src/Main.hs
index bcb1f00..61dc3bc 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -37,6 +37,33 @@ splitOn spl (x:xs)
     | otherwise = let (r : rs) = splitOn spl xs in (x:r) : rs
 
 
+usageString :: String
+usageString =
+    "\x1B[1mMeta-commands\x1B[0m\n\
+    \  env          -- Show the current environment\n\
+    \  exit         -- Exit program immediately\n\
+    \  undo         -- Undo last operation\n\
+    \  focus \x1B[4mx\x1B[0m      -- Watch and operate on given variable\n\
+    \  focus        -- Unfocus currently focused variable\n\
+    \  log          -- Print list of commands that reproduces current environment\n\
+    \  help         -- Show this help\n\
+    \\n\
+    \\x1B[1mExpression rewrite commands\x1B[0m\n\
+    \These commands operate on the currently-focused expression.\n\
+    \  rew \x1B[4mx\x1B[0m        -- Replaces occurrences of \x1B[4mx\x1B[0m with its value\n\
+    \  beta         -- Applies some beta-reductions ((\\x -> M) y => M[y/x])\n\
+    \  eta          -- Applies some eta-reductions ((\\x -> f x) => f)\n\
+    \  case         -- Evaluates case statements\n\
+    \  case!        -- Evaluates case statements, choosing first hit if multiple branches unify\n\
+    \  etacase      -- If all case branches are the same as their patterns, remove case statement\n\
+    \  casecase     -- case (case x of {A->a;B->b}) of {C->c;D->d} \n\
+    \                    => case x of {A->case a of {C->c;D->d}; B->case b of {C->c;D->d}}\n\
+    \  repeat \x1B[4mcmd\x1B[0m   -- Repeat \x1B[4mcmd\x1B[0m until no change occurs\n\
+    \\n\
+    \To evaluate a rewrite command on an unfocused variable, use:\n\
+    \  action \x1B[4mx\x1B[0m \x1B[4mcmd\x1B[0m -- Evaluate \x1B[4mcmd\x1B[0m on variable \x1B[4mx\x1B[0m"
+
+
 data AppState = AppState { asCtx :: Context, asFocus :: Maybe Name }
   deriving (Show)
 
@@ -64,6 +91,7 @@ data UserCmd = UCCmd Cmd
              | CUnFocus
              | CFocus Name
              | CLog
+             | CHelp
   deriving (Show)
 
 instance Pretty Action where
@@ -145,6 +173,7 @@ applyUserCmd appstate = \case
     CLog -> do
         mapM_ (putStrLn . pretty) $ map fst (reverse $ cStack (asCtx appstate))
         return (Right (Just appstate))
+    CHelp -> putStrLn usageString >> return (Right (Just appstate))
 
 applyUserCmds :: AppState -> [UserCmd] -> IO (Either String (Maybe AppState))
 applyUserCmds appstate [] = return (Right (Just appstate))
@@ -200,6 +229,7 @@ parseCmd ["env"] = Right CShowEnv
 parseCmd ["focus"] = Right CUnFocus
 parseCmd ["focus", name] = Right (CFocus name)
 parseCmd ["log"] = Right CLog
+parseCmd ["help"] = Right CHelp
 parseCmd ["rew", func] = Right (UCCmd (CRewrite func))
 parseCmd ["beta"] = Right (UCCmd CBeta)
 parseCmd ["eta"] = Right (UCCmd CEta)
-- 
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