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herkforth words

<lherkforth<> has a lot of the same core words as other <lforth<>s. If you are
unfamiliar with basic forth words, I recommend reading some of the <lforth
documentation<>.

It's very useful to know the <lherkforth naming conventions<>. They make it
very much easier to read code, and sometimes to find the word you're looking
for.

Speaking of finding words, check out the search commands in <lherkforth command
keys<>.

These words don't (normally) apear in other <lforth<>s.

See <lherkforth deferred words<>

<lherkforth<> doesn't have normal comparison operators (e.g. <c<< > =<>) Instead it
checks conditions as part of the control flow words if:

<c<<if >if <<>if <<=if >=if 0if<>

and <c;<> (exit) words:

<c0=; <<; >; <<>; if;<>

<c<<;<> is equivalent to (in ans forths): <c<< if exit then<>

There are two more which are like the above (they exit on a condition) except
that they only <cdrop<> if if TOS is zero:

<c0; ?;<>

<c0;<> is like <c0=;<> except that it does not drop TOS unless it's zero. So
it's equivalent to the following ans code: <cdup 0 = if drop exit then<>

<c?;<> is like <cif;<> except it does not drop TOS unless it's zero, So it is
equivalent to the following in ans code: <cdup if exit then drop<>

<hLoops<>

<lherkforth<> has two types of loops. Counted (<cfor<>/<cnext<>) and tail
recursion.

Counted loops:

<: 5stars <><] 5 for $2a emit next ;<>

Note: <c5 for<> will cause the code between <cfor<> and <cnext<> to execute
<c5<> times. I would like to emphesise that it's <c5<> times, because gforth
and probably other forths would execute it 6 times (go figure.)

Tail recursion: You don't have to do anything fancy to do tail recursion.
<lherkforth<> automagically turns a call just before a <c;<> into a branch. So
you can simply:

<: stars <><] $2a emit 1- 0; stars ;<>

In addition to the normal <c@<> and <c!<> <lherkforth<> also has an A (address)
register. You may have heard of this from <lcolorforth<> and some other forths,
but here's a quick intro:

<c>a<> pops TOS into the A register.

<c!a<> stores TOS to the address in the A register

<c@a<> fetches from the address in the A register

<ca<> pushes A onto the stack

The A register is very useful for incrementing stores/fetches.

<c+!<> increments the address in the A register (by one word) and stores to
that address.

<ch+!<> increments the address in the A register (by a <eh<>alf-word) and
stores a <eh<>alf-word to that address.

<cb+!<> increments the address in the A register (by one) and stores a <eb<>yte
to that address.

As PPC has no post-increment or post-decrement stores or fetches, it's usually
best to decrement the pointer before you use it. Herkforth has these words:
<cb>a h>a w>a<> which push TOS into the A register, and decrement it by 1, 2
and 4 bytes respectively.

While we're on the subject of stores and fetches, you can add an <ch<> to make
it store/fetch a Half word (two bytes), or a <cb<> prefix makes it just one
Byte. Thus, <lherkforth<> has the following words: <c b! b@ h! h@ b+! b-! h+!
h+@<>. An <ca<> postfix indicates that the store/fetch uses the A register,
thus we have: <c!a b!a<> and <ch!a<>

Read the <lherkforth naming conventions<> for more details.

<crot else do loop immediate does> begin until while word parse<>

These are missing on purpose, and I intend not to ever add them.

<lherkforth immediates<> work without the word <cimmediate<>.

You <ldon't need else<>.

<lherkforth variables<> work without the word <cvariable<>.

<lherkforth<>

<lforth<>

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