Parser (version 2)
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program = succeed Program `ap` definitions 
                          `ap` expression 
                          `chk` eof 

definitions = many definition 

definition = succeed Definition `ap` identifier 
                                `ap` identifiers 
                                `chk` literal "=" 
                                `ap` expression 
                                `chk` literal ";" 

identifiers = many identifier

expression = 
  succeed Application `ap` identifier 
                      `ap` atomicExpression s 
  `alt` 
  atomicExpression 

atomicExpressions = many atomicExpression

atomicExpression = 
    succeed Number `ap` number 
    `alt` succeed id `chk` literal "(" 
                     `ap` expression 
                     `chk` literal ")" 

identifier = satisfy (all isAlpha) 

number = succeed read `ap` satisfy (all isDigit)