asm.md

Pravda Assembler

Pravda assembler (pasm) is a text representation of Pravda VM bytecode.

Let's consider one simple program written in pasm:

/* My program */
jump @main
@ok:
push "good"
jump @end
@main:
push 2
mul
push 8
gt
jumpi @ok
push "bad"
@end:

It pops item from the stack and multiplies it by 2. If it is less than 8 it pushes "good" to the stack, else it pushes "bad".

pasm operations are easy to understand. There're several things that differ from low-level bytecode:

1. You can define labels: @my_label:.
2. Jump to defined labels jump @my_label. Jump with condition jumi @my_label and jump to functions with preserved call-stack call @my_label.
3. Push primitive to the stack:push [primitive]. Or put item to the heap: new [data] (in this case reference to data will be pushed to the stack).
4. Write comments: /* a comment */.
5. Work with structs: struct_mut [primitive], struct_get [primitive]. This will produce STRUCT_MUT_STATIC and STRUCT_GET_STATIC opcodes which take key for struct field from bytecode. You can write struct_mut or struct_get without [primitive] literal. In this case STRUCT_MUT and STRUCT_GET opcodes are used and key is taken from stack.
6. Use regular orphan opcodes.
7. Add meta information via meta <meta>, see <meta> definition for details.

See also string data encoding.