Where does "templates/wrappers.hs" live, in a Happy project?

Question

I'm trying to make a parser using Alex with Happy. I'm following the instructions from this post, but having trouble. I'm trying to track down the source of the following type error:

templates/wrappers.hs:234:9:
    Couldn't match type ‘Token’ with ‘Int -> Alex Token’
    Expected type: AlexInput -> Int -> Alex Token
      Actual type: String -> Token
    In a stmt of a 'do' block: action (ignorePendingBytes inp) len
    In the expression:
      do { alexSetInput inp';
           action (ignorePendingBytes inp) len }
    In a case alternative:
        AlexToken inp' len action
          -> do { alexSetInput inp';
                  action (ignorePendingBytes inp) len }

My lexer is in src/AnsiParser/FrontEnd/Lex.x. So I took a look in dist/build/AnsiParser/FrontEnd/Lex.hs, and all I can find is:

{-# LINE 1 "templates/wrappers.hs" #-}
{-# LINE 1 "templates/wrappers.hs" #-}

But I can't find any files named "wrapper.hs" on my system. How can I track down the cause of this error?

In case it's useful, here's a reduced version of my Parse.y:

{
module AnsiParser.FrontEnd.Parse where
import AnsiParser.FrontEnd.Lex
}

%name parseTokens
%tokentype { Token }
%lexer { lexWrap } { alexEOF }
%monad { Alex }
%error { parseError }

%token
  -- tokens

%%
-- rules

{
parseError :: Token -> Alex a
parseError tokens = error ("Error!" ++ show tokens)
}

And Lex.x:

{
module AnsiParser.FrontEnd.Lex where
}

%wrapper "monad"

tokens :-
  -- tokens

{
data Token
  = -- token types
  | TokenEOF
  deriving (Show)

scanTokens = alexMonadScan

lexWrap :: (Token -> Alex a) -> Alex a
lexWrap = (alexMonadScan >>=)

alexEOF :: Alex Token
alexEOF = return TokenEOF
}

Answer 1

You can find the source for template/wrappers.hs in the alex repo:

https://github.com/simonmar/alex/tree/master/templates

Running alex on your provided Lex.x gave me this error:

alex: (Array.!): undefined array element

If you give me a working example I can track down your problem.