Why does Text.Regex.Posix = ~ match characters with \ d?

Question

Can someone explain how this interaction in ghci is possible?

*Main Text.Regex.Posix> "d1" =~ "\\d" :: String
"d"
*Main Text.Regex.Posix> "d1" =~ "\\d" :: Int
1

I thought it \dcorresponded to a number, so I do not understand how it can correspond to a character d, but not to the character 1present in the string.

Note. Using ghci 7.10.3

Answer 1

Text.Regex.Posix c posix regex api. regex POSIX \d , [:digit:] POSIX, , . [[:digit:]]. [0-9] ASCII .

\d , Text.Regex.PCRE.