towers-of-hanoi.taq

$ java -jar taq.jar towers-of-hanoi

Running query towers_of_hanoi1 in global scope 
Move disk 1 from rod A to rod C

Running query towers_of_hanoi2 in global scope 
Move disk 1 from rod A to rod B
Move disk 2 from rod A to rod C
Move disk 1 from rod B to rod C

Running query towers_of_hanoi3 in global scope 
Move disk 1 from rod A to rod C
Move disk 2 from rod A to rod B
Move disk 1 from rod C to rod B
Move disk 3 from rod A to rod C
Move disk 1 from rod B to rod A
Move disk 2 from rod B to rod C
Move disk 1 from rod A to rod C

Description

towers-of-hanoi.taq demonstrates flow recursion and how to supply the initial parameters to start the recursion. The puzzle involves moving a stack of disks across three rods following some simple rules, the main one being that only one disc can be moved at a time.

Queries towers_of_hanoi 1,2 and 3 solve the puzzle for the number of discs set as a query parameter

query towers_of_hanoi3(tower_of_hanoi)(n=3)

The first 4 terms of the “tower_of_hanoi” flow are call parameters. The first parameter identifies a disc. The next 3 are from_rod, to_rod, aux_rod, each identifying a different rod. The iniatial value for these parameters in supplied by template parameters appended to the flow

flow tower_of_hanoi (
…
)(from_rod=“A”, to_rod=“C”, aux_rod=“B”)

Apart from getting recursion started, template parameters provide a way to advertize aspects of a template that are intended to be customized, or are exprected to vary according to circumstances.

flow tower_of_hanoi
(

n, from_rod, to_rod, aux_rod,
?? (n == 1)

print("Move disk 1 from rod ", from_rod, " to rod ", to_rod),

?: n == 1,
tower_of_hanoi(disk=n - 1, from=from_rod, to=aux_rod, aux=to_rod),
print("Move disk ", n, " from rod ", from_rod, " to rod ", to_rod),
tower_of_hanoi(disk=n - 1, from=aux_rod, to=to_rod, aux=from_rod)

)(from_rod="A", to_rod="C", aux_rod="B")

query towers_of_hanoi1(tower_of_hanoi)(n=1)
query towers_of_hanoi2(tower_of_hanoi)(n=2)
query towers_of_hanoi3(tower_of_hanoi)(n=3)