What would be the Hardy-Weinberg equilibrium condition for a population of haploid organism?
What is HW rule?

HW rule is a rule allowing one to compute genotype frequencies from allele frequencies and vice-versa. See Solving Hardy Weinberg problems and eventually Assumptions of Hardy-Weinberg rule for more information.

HWr in haploid organisms

In haploid individuals, the genotype frequencies and the allele (or haplotype) frequencies is the exact same thing! This is because the genotype is a simple haplotype. In other words, once you have the allele frequency, you necessarily have the genotype frequencies without need for any calculation. We can consider the haploid organism would display a special case of HW rule, where there is no assumption and where 

$$p = f_{A}$$

$$q = f_{B} = 1 - f_{A}$$

, where $f_{A}$ is the frequency of the genotype carrying the allele A and $p$ is the frequency of the allele A. $f_{B}$ is the frequency of the genotype carrying the allele B and $q$ is the frequency of the allele B.