From f9dc730f88274bd54e3c7065005bfd6ba5c01ae4 Mon Sep 17 00:00:00 2001
From: Chris Pressey <cpressey@catseye.tc>
Date: Wed, 13 Dec 2017 16:11:02 +0000
Subject: [PATCH] `copy []+y, a` to indirectly read byte into the `a` register.

---
 HISTORY.md                      |  1 +
 eg/proto-game.60p               |  4 +++-
 src/sixtypical/compiler.py      |  5 ++++-
 tests/SixtyPical Compilation.md | 10 ++++++----
 4 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/HISTORY.md b/HISTORY.md
index 0c66e7f..0259d3c 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -11,6 +11,7 @@ History of SixtyPical
 *   Can `copy` a literal word to a word table.
 *   Subtract word (constant or memory location) from word memory location.
 *   `trash` instruction explicitly indicates a value is no longer considered meaningful.
+*   `copy []+y, a` can indirectly read a byte value into the `a` register.
 *   Fixed bug which was preventing `if` branches to diverge in what they initialized,
     if it was already initialized when going into the `if`.
 *   Fixed a bug which was making it crash when trying to analyze `repeat forever` loops.
diff --git a/eg/proto-game.60p b/eg/proto-game.60p
index d53c111..7ffd61c 100644
--- a/eg/proto-game.60p
+++ b/eg/proto-game.60p
@@ -235,7 +235,9 @@ routine player_logic
         add ptr, new_pos
         ld y, 0
 
-        // copy [ptr] + y, a
+        // check collision.
+        copy [ptr] + y, a
+
         // cmp a, 32
         // if z {
         //     copy new_pos, pos
diff --git a/src/sixtypical/compiler.py b/src/sixtypical/compiler.py
index 99eb5cc..1888cd7 100644
--- a/src/sixtypical/compiler.py
+++ b/src/sixtypical/compiler.py
@@ -385,7 +385,10 @@ class Compiler(object):
                 else:
                     raise NotImplementedError((src, dest))
             elif isinstance(src, IndirectRef) and isinstance(dest, LocationRef):
-                if dest.type == TYPE_BYTE and isinstance(src.ref.type, PointerType):
+                if dest == REG_A and isinstance(src.ref.type, PointerType):
+                    src_label = self.labels[src.ref.name]
+                    self.emitter.emit(LDA(IndirectY(src_label)))
+                elif dest.type == TYPE_BYTE and isinstance(src.ref.type, PointerType):
                     src_label = self.labels[src.ref.name]
                     dest_label = self.labels[dest.name]
                     self.emitter.emit(LDA(IndirectY(src_label)))
diff --git a/tests/SixtyPical Compilation.md b/tests/SixtyPical Compilation.md
index 9382fb9..91fedfa 100644
--- a/tests/SixtyPical Compilation.md	
+++ b/tests/SixtyPical Compilation.md	
@@ -1005,7 +1005,7 @@ Write stored value through a pointer.
     = $081A   STA ($FE),Y
     = $081C   RTS
 
-Read through a pointer.
+Read through a pointer, into a byte storage location, or the `a` register.
 
     | buffer[2048] buf
     | pointer ptr @ 254
@@ -1019,15 +1019,17 @@ Read through a pointer.
     |     ld y, 0
     |     copy ^buf, ptr
     |     copy [ptr] + y, foo
+    |     copy [ptr] + y, a
     | }
     = $080D   LDY #$00
-    = $080F   LDA #$1D
+    = $080F   LDA #$1F
     = $0811   STA $FE
     = $0813   LDA #$08
     = $0815   STA $FF
     = $0817   LDA ($FE),Y
-    = $0819   STA $101D
-    = $081C   RTS
+    = $0819   STA $101F
+    = $081C   LDA ($FE),Y
+    = $081E   RTS
 
 Add a word memory location, and a literal word, to a pointer, and then read through it.
 Note that this is *not* range-checked.  (Yet.)