[s|Hello, %s! (%d people greeted)|] :: ... -> String

This formatter follows the guidelines listed here, with some caveats:

• Hexadecimal floating point isn't supported. I'm not convinced anyone actually uses this and there doesn't appear to be anything in base to produce it.
• %p (pointer) and %n (store number of printed characters) are not supported for obvious reasons.
• %.0e shows at least one decimal place despite this special case not appearing anywhere in the spec. This is a bug in formatRealFloat. As a result, %e and %#e have identical behavior.

%c     :: Char
%s     :: String

%?     :: Show a => a

%u     :: Natural

%d, %i :: Integral i => i
%o     :: Integral i => i
%x, %X :: Integral i => i

%e, %E :: RealFloat f => f
%f, %F :: RealFloat f => f
%g, %G :: RealFloat f => f

[st|Hello, %s! (%d people greeted)|] :: ... -> Text

[sb|Hello, %s! (%d people greeted)|] :: ... -> ByteString

The resulting string is UTF8-encoded.

[hp|Hello, %s! (%d people greeted)|] :: MonadIO m => Handle -> ... -> m ()

Prints the produced string to the provided Handle. Like C printf, newline is not appended.

[p|Hello, %s! (%d people greeted)|] :: MonadIO m => ... -> m ()

[p|...|] arg1 arg2...

is equivalent to

[hp|...|] stdout arg1 arg2...