[Haskell-cafe] Indentation problem using Happy

[Amy de Buitléir]

I'm trying to use Happy for the first time, and I'm having trouble with this
very simple example:

===== BEGIN: PolyParser.y =====
{
module Main where

import Char ( isAlpha, isDigit, isSpace )
}
%name calc
%tokentype { Token }
%error { parseError }
%token 
      id              { TokenId $$ }
      ','             { TokenCOMMA }
      wombat          { TokenWombat $$ }
%%
Poly    : id ',' wombat
{
parseError :: [Token] -> a
parseError _ = error "Parse error"

data Poly = Poly Int String deriving Show

data Token
      = TokenId Int
      | TokenCOMMA
      | TokenWombat String deriving Show

lexer :: String -> [Token]
lexer [] = []
lexer (c:cs) 
      | isSpace c = lexer cs
      | isAlpha c = lexVar (c:cs)
      | isDigit c = lexNum (c:cs)
lexer (',':cs) = TokenCOMMA : lexer cs

lexNum cs = TokenInt (read num) : lexer rest
      where (num,rest) = span isDigit cs

lexVar cs =
   case span isAlpha cs of
      (wombat,rest) -> TokenWombat wombat : lexer rest
      (id,rest)   -> TokenId id : lexer rest
      
main = getContents >>= print . calc . lexer
}
===== END: PolyParser.y =====

The resulting PolyParser.hs has an indentation problem (second-to-last line,
below), so it won't compile.

happyReduce_1 = happySpecReduce_3  4 happyReduction_1
happyReduction_1 _
        _
        _
         =  HappyAbsSyn4
                 (parseError :: [Token] -> a
parseError _ = error "Parse error"

Thank you in advance to anyone who can tell me where I've gone wrong.