First, the header describing the library.
( ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ) ( do ... until ) ( ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ) ( Value n is taken from the stack and stored to a virtual ) ( variable. When this number is equal to the TOS at the time ) ( until is executed, the loop terminates. ) ( ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ )
Start a private namespace.
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Two definitions are defined. First, skipped-nop:
: skipped-nop ( - ) 8 , here 2 + , 0 , ;
Taking this piece by piece:
8 , ::: JUMP opcode [ngaro] here 2 + , ::: Target for jump. Skip over the next cell. 0 , ::: NOP opcode
Next is virtual-var
: virtual-var ( R: -a C: -aa ) here dup 1- dup literal, ;
Again, breaking it down:
here dup 1- ::: Get address of the previous cell
dup literal, ::: Compile it as a literal, and leave a
::: copy on the stack for later use
The rest of the words will be visible in the dictionary:
---reveal---
Now on to the main words. First up do:
: do ( R: nn-n? C: -aa )
` 2dup ` >if
skipped-nop
virtual-var ` ! ; compile-only
This is a compiler macro (compile-only), and will lay down some code in any definition using it.
` 2dup ` >if ::: Compile a call to 2dup and execute >if when the macro is run skipped-nop ::: Call skipped-nop to lay down a jump and virtual variable virtual-var ` ! ::: Get a reference to the virtual variable and store TOS to it
The word until is also a compiler macro:
: until ( R: ?n- C: aa- ) ` dup literal, ` @ ` > ` if swap 8 , 3 + , ` then ` drop ` else ` 2drop ` then ; compile-only
Breaking until down:
` dup ::: literal, ` @ ::: ` > ` if ::: swap 8 , 3 + , ::: ` then ` drop ::: ` else ` 2drop ::: ` then :::
Finally, close out the private namespace, leaving only the public words visible:
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