scopes.md

Scopes

The assembler supports lexical scopes. Each file has it's own scope, and each block within a file contains it's own scope. A file for our purposes can be considered just another block.

A scope is defined to be the span in which an identifier is valid.

Blocks

A block is simply a list of statements delimited by { and }. This is quite similar to C blocks.

A block can reference identifiers defined in it's containing block.

For example, this results in r0 containing the value 123:

value = 123;
{
    ld r0, value;
}

An identifier defined in a child block cannot be referenced from the parent block.

For example, this DOES NOT ASSEMBLE:

{
    value = 123;
}
ld r0, value;

Warning

This example will not assemble.

Note

There is a mechanism called block exports that allows a value to be referenced from the parent scope, as detailed in the Imports and Exports document.

Block-scoped Imports

Blocks can contain import statements, in which case the imported identifiers are only valid within that block.

For example:

{
    import print from "lib/print.asm";
  
        ld r0, string;
        push r0;
        ld pc.link, print;

    end:
        ld pc, end;
}
// cannot reference print from this scope!

string: "hello_world!\n\0";