From 054619d2fb309c662b3babb5df699619cc6e9dd8 Mon Sep 17 00:00:00 2001
From: Lucian Mogosanu <lucian.mogosanu@gmail.com>
Date: Sat, 13 Dec 2014 22:45:22 +0200
Subject: [PATCH] ZXS: Add fetcher

---
 src/ZXS/Fetch.hs   |   22 ++++++++++++++++++++++
 src/ZXS/Machine.hs |   11 ++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 src/ZXS/Fetch.hs

diff --git a/src/ZXS/Fetch.hs b/src/ZXS/Fetch.hs
new file mode 100644
index 0000000..d1889e0
--- /dev/null
+++ b/src/ZXS/Fetch.hs
@@ -0,0 +1,22 @@
+module ZXS.Fetch where
+
+-- opcode fetcher, with some side effects in the CPU
+
+import Data.Word
+import Control.Monad.IO.Class (liftIO)
+
+import Z80.CPU
+import Z80.Microcode
+import ZXS.Machine
+import ZXS.RAM
+
+fetch :: ZXS Word8
+fetch = do
+  Spectrum cpu mainMem <- getZXState
+  -- get pc
+  let pc = getPC cpu
+  -- getch byte
+  b <- liftIO $ ramGetByte mainMem pc
+  -- update pc
+  modifyCPU $ flip modifyPC (+ 1)
+  return b
diff --git a/src/ZXS/Machine.hs b/src/ZXS/Machine.hs
index f43cd26..1130470 100644
--- a/src/ZXS/Machine.hs
+++ b/src/ZXS/Machine.hs
@@ -16,7 +16,16 @@ data Spectrum = Spectrum
 
 -- the ZXS transformer
 newtype ZXST m a = ZXST { unZXST :: StateT Spectrum m a }
-  deriving (Monad, Functor, Applicative, MonadIO)
+  deriving (MonadState Spectrum, Monad, Functor, Applicative, MonadIO)
 
 -- for now we "fall back" to IO as the default inner monad
 type ZXS a = ZXST IO a
+
+modifyCPU :: (CPU -> CPU) -> ZXS ()
+modifyCPU f = modify $ \ spc -> spc { zxCPU = f $ zxCPU spc }
+
+modifyMainMem :: (RAM -> RAM) -> ZXS ()
+modifyMainMem f = modify $ \ spc -> spc { zxMainMem = f $ zxMainMem spc }
+
+getZXState :: ZXS Spectrum
+getZXState = get
-- 
1.7.10.4