jurjen@cwi.nl (Jurjen N.E. Bos) (02/23/88)
I have forgotten to say the following things:
READ displays the contents of memory addresses *backwards*:
this is very handy because addresses are stored backwards, and thus
directly readable. Furthermore, READ increments the address with the amount
it displays, so that it is easy to continue.
A handy way of getting an address of a object is putting it in a brand new
variable and looking at address #4FFB0: this gives the top 80 nibbles of
RAM. You'll soon find out how variables are stored and see your object.
Example {+} 1 GET gives a single +. Putting this in the variable TP gives
as result of #4FFB0 READ:
03A00 202D5 C0250 54020
008B0 2F902 7F1F1 A2B62
7F4E2 79BC2 7F341 783F1
7B0B2 79BC1 783F4 44145
This means: (still backwards)
03A 002 02D5C 02 50 54 02
3A 2 function 2 P T 2
Otherwise said: function number 3A,2 stored in variable PT. The name
PT has two letters.
More informative is << + >> 'TP' STO #$FFB0 READ:
02F90 27F1F 18F9D 27F0A
end >> + <<
02C67 02 50 54 02
program 2 P T 2
This learns us that the function + is to be found in ROM at 18F9D.
You'll find there the code that does +, written normal way:
02C67 program
1C3A5 check two levels stack & save LAST registers
1C6FA CASE statement on type of top levels
06E00 pointer 00011: this means two reals
1EC68 + for two reals
06E0A pointer 00012: real and complex
3323C + for real and complex
...
The amount of FORTH code is almost endless: you don't have to know
the machine code to come rather far (but it helps).
Hope you'll succeed. -- Jurjen.