Commit 0e9a887ac5cbf569994468e821df8637a5b2f7ea - SixtyPical

Update the spec re what literal integers in the code mean. Chris Pressey 4 years ago

1 changed file(s) with 18 addition(s) and 9 deletion(s). Raw diff Collapse all Expand all

+18

-9

doc/SixtyPical.md less more

13	13	Types
14	14	-----
15	15
16		There are seven types in SixtyPical:
	16	There are five primitive types in SixtyPical:
17	17
18	18	* bit (2 possible values)
19	19	* byte (256 possible values)
20		* byte table (256 entries, each holding a byte)
21	20	* word (65536 possible values)
22		* word table (256 entries, each holding a word)
23	21	* routine (code stored somewhere in memory, read-only)
24	22	* vector (address of a routine)
	23
	24	There is also one type constructor:
	25
	26	* X table (256 entries, each holding a value of type X)
	27
	28	This constructor can only be applied to bytes or words.
25	29
26	30	Memory locations
27	31	----------------

110	114	trashes y
111	115	@ $c000
112	116
113		> TODO: need to confirm this, but, the rule is:
114		>
115		> * If it is NAMED, it is a memory address.
116		> * If it is a LITERAL INTEGER, it is an immediate value.
117		>
118		> However, this really needs a review, deep in the code, for how this is implemented.
	117	Note that in the code of a routine, if a memory location is named by a
	118	user-defined symbol, it is an address in memory, and can be read and written.
	119	But if it is named by a literal integer, either decimal or hexadecimal, it
	120	is a constant and can only be read (and when read always yields that constant
	121	value. So, for instance, to read the value at `screen` above, in the code,
	122	you would need to reference the symbol `screen`; attempting to read 1024
	123	would not work.
	124
	125	This is actually useful, at least at this point, as you can rely on the fact
	126	that literal integers in the code are always immediate values. (But this
	127	may change at some point.)
119	128
120	129	Routines
121	130	--------