Generating template with some logic via HStringTemplate

Question

Here is some invalid HStringTemplate syntax:

option_a = $options.a$
option_b = $options.b$
$if options.option_c_is_needed$
option_c = $option.c$
$end$

In other words, part of template file should be created only if specific predicate is true. How can it be achieved via HStringTemplate? If there is no way to do that in it, what libraries could be helpful here?

May be there is some analog of erubis mechanism with ability to use haskell code inside template files?

Answer 1

Hammar's comment is correct. See below:

*Main Text.StringTemplate> render $ setAttribute "optSet" False $ (newSTMP "OptSet: $if(optSet)$Option Is Set$else$Option Isn't Set$endif$" :: StringTemplate String)
"OptSet: Option Isn't Set"
*Main Text.StringTemplate> render $ setAttribute "optSet" True  $ (newSTMP "OptSet: $if(optSet)$Option Is Set$else$Option Isn't Set$endif$" :: StringTemplate String)
"OptSet: Option Is Set"