Hi folks,
I'm new to the list. I've been reading CTM, and I attempted to solve
Exercise 9 in Chapter 4. This involves creating a "gate" that adds together
two numbers by chaining full adders. I decided to encode the multiple bits
of a number as a tuple. Unfortunately, although my code produces the correct
result, it runs away with creating new threads. Although I've figured out
that it keeps extending Cs, I don't know why. The key procedure to look at
is ChainedAdder. The top section (up through the declaration of FullAdder)
is copied straight from 4.3.5.
I've run this through the debugger, and I can watch some threads being
created, but the runaway threads seem to be coming from nowhere. Any ideas?
Thanks,
Lyle Kopnicky
declare GateMaker
fun {GateMaker F}
fun {$ Xs Ys}
fun {GateLoop Xs Ys}
case Xs#Ys of (X|Xr)#(Y|Yr) then
{F X Y}|{GateLoop Xr Yr}
end
end
in
thread {GateLoop Xs Ys} end
end
end
declare AndG OrG NandG NorG XorG
AndG ={GateMaker fun {$ X Y} X*Y end}
OrG ={GateMaker fun {$ X Y} X+Y-X*Y end}
NandG={GateMaker fun {$ X Y} 1-X*Y end}
NorG ={GateMaker fun {$ X Y} 1-X-Y+X*Y end}
XorG ={GateMaker fun {$ X Y} X+Y-2*X*Y end}
declare FullAdder
proc {FullAdder X Y Z ?C ?S}
K L M
in
K={AndG X Y}
L={AndG Y Z}
M={AndG X Z}
C={OrG K {OrG L M}}
S={XorG Z {XorG X Y}}
end
% Z0s=0|0|0|...
% {FullAdder X1s Y1s Z0s C1s S1s}
% {FullAdder X2s Y2s C1s C2s S2s}
% {FullAdder X3s Y3s C2s C3s S3s}
% {FullAdder Z0s Z0s C3s _ S4s}
declare Repeat
fun lazy {Repeat F}
{F}|{Repeat F}
end
declare Zeros
Zeros={Repeat fun {$} 0 end}
declare LMap
fun lazy {LMap Xs F}
case Xs
of nil then nil
[] X|Xr then {F X}|{LMap Xr F}
end
end
declare ChainedAdder
local
Bit
in
fun {Bit N Xs}
{LMap Xs fun {$ X} X.N end}
end
proc {ChainedAdder Xs Ys ?Ss}
N Cs
in
N={Width Xs.1}
Cs={Repeat fun {$} {MakeTuple '#' N+1} end}
Ss={Repeat fun {$} {MakeTuple '#' N+1} end}
{Browse cs#Cs}
{Browse ss#Ss}
{Bit 1 Cs}=Zeros
for I in 1..N do
{FullAdder {Bit I Xs} {Bit I Ys} {Bit I Cs} {Bit I+1 Cs} {Bit I
Ss}}
end
{FullAdder Zeros Zeros {Bit N+1 Cs} _ {Bit N+1 Ss}}
end
end
declare
X=(0#1#1)|_
Y=(1#0#1)|_
S
{ChainedAdder X Y S}
{Browse inp(X Y)#sum(S)}
% END OF FILE
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