VIC-20 example and rewrite docs.

README.md

@@ -84,6 +84,7 @@ is probably NP-complete.  But doing it adequately is probably not that hard.
 *   `const`s that can be used in defining the size of tables, etc.
 *   Tests, and implementation, ensuring a routine can be assigned to a vector of "wider" type
 *   Related: can we simply view a (small) part of a buffer as a byte table?  If not, why not?
+*   Related: add constant to buffer to get new buffer.  (Or to table, but... well, maybe.)
 *   Check that the buffer being read or written to through pointer, appears in approporiate inputs or outputs set.
     (Associate each pointer with the buffer it points into.)
 *   `static` pointers -- currently not possible because pointers must be zero-page, thus `@`, thus uninitialized.
@@ -94,5 +95,6 @@ is probably NP-complete.  But doing it adequately is probably not that hard.
 *   Possibly `ld x, [ptr] + y`, possibly `st x, [ptr] + y`.
 *   Maybe even `copy [ptra] + y, [ptrb] + y`, which can be compiled to indirect LDA then indirect STA!
 *   Optimize `ld a, z` and `st a, z` to zero-page operations if address of z < 256.
+*   Include files?
 
 [VICE]: http://vice-emu.sourceforge.net/

eg/README.md

@@ -1,7 +1,20 @@
 This directory contains SixtyPical example programs, categorized
-in subdirectories by the machine architecture.
+in subdirectories by machine architecture.
 
-In the [c64](c64/) directory are programs that run on the Commodore 64:
+### rudiments
+
+In the [rudiments](rudiments/) directory are programs which are not for
+any particular machine, but meant to demonstrate the features of SixtyPical.
+Some are meant to fail and produce an error message.  Others can run on
+any architecture where there is a routine at 65490 which outputs the value
+of the accumulator as an ASCII character.
+
+### c64
+
+In the [c64](c64/) directory are programs that run on the Commodore 64.
+The directory itself contains some simple demos, for example
+[hearts.60p](c64/hearts.60p), while there are subdirectories for more
+elaborate demos:
 
 *   [demo-game](c64/demo-game/): a little game-like program written as a
     "can we write something you'd see in practice?" test case for SixtyPical.
@@ -12,17 +25,17 @@ In the [c64](c64/) directory are programs that run on the Commodore 64:
     
     The second version of Ribos has been translated to SixtyPical.
     
-*   [petulant](c64/petulant/) -- "The PETulant Cursor", a tiny (44 bytes)
+*   [petulant](c64/petulant/): "The PETulant Cursor", a tiny (44 bytes)
     "display hack". Originally written in the late 80's. Rewritten with
     the P65 assembler (now Ophis) and re-released on April 1st, 2008 (a
     hint as to its nature).
     
     Translated to SixtyPical (in 2018), it's 48 bytes.
 
-In the [rudiments](rudiments/) directory are programs which are not for
-any particular machine, but meant to demonstrate the features of SixtyPical.
-Some are meant to fail and produce an error message.  Others can run on
-any architecture where there is a routine at 65490 which outputs the value
-of the accumulator as an ASCII character.
+### vic20
+
+In the [vic20](vic20/) directory are programs that run on the
+Commodore VIC-20.  The directory itself contains some simple demos,
+for example [hearts.60p](vic20/hearts.60p).
 
 [Ophis]: http://michaelcmartin.github.io/Ophis/

eg/vic20/hearts.60p

@@ -0,0 +1,16 @@
+// Displays 256 hearts at the top of the VIC-20's screen.
+
+// Define where the screen starts in memory:
+byte table[256] screen @ 7680
+
+routine main
+  // These are the values that will be written to by this routine:
+  trashes a, x, z, n, screen
+{
+    ld x, 0
+    ld a, 83    // 83 = screen code for heart
+    repeat {
+        st a, screen + x
+        inc x
+    } until z   // this flag will be set when x wraps around from 255 to 0
+}