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Program code as data file

Microsoft Basic, e.g. on 8 bit Commodore machines, supported reading and writing program files on floppy disk like sequential data files.

OPEN 2,8,2,"EXAMPLE,P,W"

would open a file named EXAMPLE with type PRG for writing. Then one could create a program with a couple of PRINT# instructions, and CLOSE it, it'd show up as an executable file on disk. It should be written as it'd appear on the memory, i.e. line numbers as 16 bit integers, keywords should be tokenized etc.

Chain-loading or chaining

The LOAD instruction, when issued in a running program

999 LOAD "EXAMPLE",8

loads the named program from disk, replacing the running one, and starts executing it at the first instruction. As long as the loaded program is smaller than the first one, variables would be preserved, so they can communicate that way with each other.

Read-modify-write

A program could as well open the file containing its own code, read it one line at a time, modify some stuff on the fly, write it back to another file, then chain-load it.

Microsoft Basic, e.g. on 8 bit Commodore machines, supported reading and writing program files on floppy disk like sequential data files.

OPEN 2,8,2,"EXAMPLE,P,W"

would open a file named EXAMPLE with type PRG for writing. Then one could create a program with a couple of PRINT# instructions, and CLOSE it, it'd show up as an executable file on disk. It should be written as it'd appear on the memory, i.e. line numbers as 16 bit integers, keywords should be tokenized etc.

The LOAD instruction, when issued in a running program

999 LOAD "EXAMPLE",8

loads the named program from disk, replacing the running one, and starts executing it at the first instruction. As long as the loaded program is smaller than the first one, variables would be preserved, so they can communicate that way with each other.

Program code as data file

Microsoft Basic, e.g. on 8 bit Commodore machines, supported reading and writing program files on floppy disk like sequential data files.

OPEN 2,8,2,"EXAMPLE,P,W"

would open a file named EXAMPLE with type PRG for writing. Then one could create a program with a couple of PRINT# instructions, and CLOSE it, it'd show up as an executable file on disk. It should be written as it'd appear on the memory, i.e. line numbers as 16 bit integers, keywords should be tokenized etc.

Chain-loading or chaining

The LOAD instruction, when issued in a running program

999 LOAD "EXAMPLE",8

loads the named program from disk, replacing the running one, and starts executing it at the first instruction. As long as the loaded program is smaller than the first one, variables would be preserved, so they can communicate that way with each other.

Read-modify-write

A program could as well open the file containing its own code, read it one line at a time, modify some stuff on the fly, write it back to another file, then chain-load it.

Source Link
followed Monica to Codidact
followed Monica to Codidact
  • 2.9k
  • 1
  • 17
  • 20

Microsoft Basic, e.g. on 8 bit Commodore machines, supported reading and writing program files on floppy disk like sequential data files.

OPEN 2,8,2,"EXAMPLE,P,W"

would open a file named EXAMPLE with type PRG for writing. Then one could create a program with a couple of PRINT# instructions, and CLOSE it, it'd show up as an executable file on disk. It should be written as it'd appear on the memory, i.e. line numbers as 16 bit integers, keywords should be tokenized etc.

The LOAD instruction, when issued in a running program

999 LOAD "EXAMPLE",8

loads the named program from disk, replacing the running one, and starts executing it at the first instruction. As long as the loaded program is smaller than the first one, variables would be preserved, so they can communicate that way with each other.