The input to Happy is a text file containing the grammar of the language you want to parse, together with some annotations that help the parser generator make a legal Haskell module that can be included in your program. This section gives the exact syntax of grammar files.

The overall format of the grammar file is given below:

<optional module header>
<directives>
%%
<grammar>
<optional module trailer>

If the name of the grammar file ends in .ly, then it is assumed to be a literate script. All lines except those beginning with a > will be ignored, and the > will be stripped from the beginning of all the code lines. There must be a blank line between each code section (lines beginning with >) and comment section. Grammars not using the literate notation must be in a file with the .y suffix.

        id      ::= alpha { idchar }
                  | ' { any{^'} | \' } '
                  | " { any{^"} | \" } "

        alpha   ::= A | B | ... | Z
                  | a | b | ... | z

        idchar  ::= alpha
                  | 0 | 1 | ... | 9
                  | _