When day is specified as 0 the quasiquoter returns a pure parser function. Otherwise day uses command line arguments to find the input file and parses it as an IO action.

A format string can optionally be specified across multiple lines. In this case the day number goes on the first line and the pattern starts on the second line. All common leading white space from all the remaining lines is trimmed off and newlines are discarded (use %n for matching newlines)

The following are identical:

example1 = [format|2021 1
    %s%n
    %s%n|]

example2 = [format|2021 1 %s%n%s%n|]

Patterns:

• %u unsigned integer as Int
• %d signed integer as Int
• %lu unsigned integer as Integer
• %ld signed integer as Integer
• %s non-empty list of non-space characters as String
• %c single, non-newline character as Char
• %a single ASCII letter as Char
• %n single newline character
• other characters match literally
• use % to escape literal matches of special characters
• @A matches the names of the constructors of type A as an A

Structures:

• p|q combine alternatives p and q
• (pq) group subpattern pq
• p* zero-to-many repititions of p as a '[]'
• p+ one-to-many repititions of p as a '[]'
• p&q zero-to-many repititions of p separated by q as a '[]'
• p! returns the characters that matched pattern p as a String