| Author |
Message |
Martin Omander (Momander)
| | Posted on Saturday, November 20, 2004 - 12:43 am: | |
Here's a ZRF syntax question from a newbie. I am trying to implement a game where legal pawn moves have to start or end adjacent to a king. It's relatively easy to figure out if the piece starts next to a king using this syntax:
(if "condition_for_start_position" n add)
Here is the implementation (dots used to preserve indentation):
(define PawnMove
..(
....(if
......(and
........(not-friend? $1)
........(or
..........(piece? King n)
..........(piece? King e)
..........(piece? King s)
..........(piece? King w)
........)
......)
......$1 add
....)
..)
)
To test a condition for the end position I would do this:
(n (if "condition_for_end_position") add)
Here is that implementation:
(define PawnMove2
..($1
....(verify not-friend?)
....(if
......(or
........(piece? King n)
........(piece? King e)
........(piece? King s)
........(piece? King w)
......)
......add
....)
..)
)
But I'm not adept enough at ZRF yet to test the condition for _both_ the start and the end position. Any suggestions?
Thanks
/Martin |
L. Lynn Smith (Interrupt27)
| | Posted on Saturday, November 20, 2004 - 1:02 am: | |
Use the VERIFY statement instead of the IF, thus:
(define PawnMove
..(
....(verify
......(and
........(not-friend? $1)
........(or
..........(piece? King n)
..........(piece? King e)
..........(piece? King s)
..........(piece? King w)
........)
......)
....)
....$1
....(verify
......(or
........(piece? King n)
........(piece? King e)
........(piece? King s)
........(piece? King w)
......)
....)
....add
..)
)
This should fulfill your requirements. |
Martin Omander (Momander)
| | Posted on Saturday, November 20, 2004 - 1:21 am: | |
Thanks for the reply! I ran the code from your posting. However, it seems to only allow pawn moves that end next to king, not ones that start next to a king. Any thoughts?
/Martin |
Martin Omander (Momander)
| | Posted on Saturday, November 20, 2004 - 1:29 am: | |
I was mistaken in my last post. The code posted only allows moves moves that start AND end next to a king. How would one go about writing code that allows moves that start OR end next to king?
/Martin |
Martin Omander (Momander)
| | Posted on Saturday, November 20, 2004 - 1:37 am: | |
OK, I think I have figured it out now. L. Lynn's code only had a "verify" in one place where an "if" was needed:
(define PawnMove
..(
....(if
......(and
........(not-friend? $1)
........(or
..........(piece? King n)
..........(piece? King e)
..........(piece? King s)
..........(piece? King w)
........)
......)
....)
....$1
....(verify
......(or
........(piece? King n)
........(piece? King e)
........(piece? King s)
........(piece? King w)
......)
....)
....add
..)
)
I still need to verify that we don't capture a friendly piece in the second part, but that shouldn't be too hard.
Again, thanks for the help!
/Martin |
L. Lynn Smith (Interrupt27)
| | Posted on Saturday, November 20, 2004 - 5:05 pm: | |
My bad. I was thinking AND instead of OR. ;-)
Glad my rambling helped. |
L. Lynn Smith (Interrupt27)
| | Posted on Saturday, November 20, 2004 - 5:16 pm: | |
But you might consider the following code:
(define PawnMove
..(
....(verify (not-friend? $1))
....(set-flag King_near
......(or
........(piece? King n)
........(piece? King e)
........(piece? King s)
........(piece? King w)
......)
....)
....$1
....(if (not-flag? King_near)
......(verify
........(or
..........(piece? King n)
..........(piece? King e)
..........(piece? King s)
..........(piece? King w)
........)
......)
....)
....add
..)
)
Double-check for syntax. |
Martin Omander (Momander)
| | Posted on Saturday, November 20, 2004 - 9:43 pm: | |
Aha, that was it! Despite the brave words in my last post that checking for not-friendly wouldn't be too hard, I wasn't able to get it right. But with your latest code snippet everything works perfectly, and I got a real-life example of flag usage as well. Just reading the language reference wasn't enough for me to understand flags.
Thanks, I really appreciate it!
/Martin |