r - `bquote` is not interpreting the styling elements within a variable

Question

I asked this question here, only to discover that it is actually not quite my problem.

The problem seems to be, that I need the variable ab and hello interpreted by bquote, but it doesn't work. How can I make bquote to interprete the variable content?

a <- "alpha"
b <- "beta"
ab <- "alpha[beta]"
hello <- "hello[hello]"
ggplot(data.frame(x=c(1), y=c(1)), aes(x, y)) + 
  geom_point() +
  labs(x = bquote(.(sym(a))[.(sym(b))]~.(sym(ab))~.(hello))) + ## will output the greek letters by "name"
  labs(y = bquote(alpha[beta]~hello[hello]))  ## the greek letter-names are replaces by the symbols

Edit:

With dipetkov's answer I did the following to define my label, which can then be simply used in ggplot's labs function. Note that the whole thing is wrapped in bquote while the the variable which needs styling is additional wrapped in .(parse_expr(paste(...)).

  ylab <- bquote(.(data$y_name[1])
                 ~.(parse_expr(paste(f(data$y_symbol[1]))))
                 ~"="~
                   "["*
                   .(data$y_unit[1])
                 *"]")
ggplot(...) + ... +
labs(y = ylab)

Edit 2: actually, the paste is unnecessary in my case.

Answer 1

Almost there... The tilde symbol, ~, doesn't print with either bquote or parse_expr (because in R it signifies a formula?). So I've substituted it with a dash, -.

library("rlang")
library("tidyverse")

ab <- "alpha[beta]"
hello <- "hello[hello]"

ggplot(data.frame(x = c(1), y = c(1)), aes(x, y)) +
  geom_point() +
  labs(x = parse_expr(paste(ab, "-", hello))) +
  labs(y = bquote(alpha[beta] ~ hello[hello]))

^{Created on 2019-11-04 by the reprex package (v0.3.0)}