[THRIFT-728] Make generated Haskell code an instance of Arbitrary

• Type: New Feature
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 0.9.2
• Component/s: Haskell - Compiler, Haskell - Library
• Labels: test

Environment

All

• Patch Info: Patch Available
• Assignee: Roger Meier
• Reporter: Aran Donohue
• Created: 08/Mar/10 00:00
• Updated: 25/Sep/14 03:18
• Resolved: 26/Aug/14 22:10

Description

The patch

• Generates Arbitrary instances for Thrift structs, enums and exceptions
• Provides Arbitrary instances for GHC's Int64, Data.Map.Map and Data.Set.Set
• Makes Thrift enums instances of Bounded and improves the Enum instance declaration

Making a type an instance of Test.QuickCheck.Arbitrary specifies how to generate random instances of the struct. This is useful for testing.

For example, consider the following simple Thrift declaration:

distributed_log.thrift

enum LogLevel { DEBUG, INFO, WARNING, ERROR }                                         
                                                                                      
typedef i32 UnixTimeStamp                                                             
                                                                                      
struct LogEntry {                                                                     
   1: LogLevel level,                                                                 
   2: UnixTimeStamp timestamp,                                                        
   3: string message                                                                  
}                                                                                     
                                                                                      
service Logger {                                                                      
   void log(1: LogEntry entry)                                                        
}

With the patch, the following program (import statements elided) is a fuzzer for the log service.

LogTest.hs

-- ripped from Test.QuickCheck.Gen.sample'                                            
infexamples ∷  Gen a →  IO [a]                                                        
infexamples (MkGen m) =                                                               
  do rnd ←  newStdGen                                                                 
     let rnds rnd = rnd1 : rnds rnd2 where (rnd1, rnd2) = split rnd                   
     return [(m r n) | (r, n) ←  rnds rnd `zip` [0,2..] ]                             
                                                                                      
infentries = infexamples (arbitrary ∷  Gen LogEntry)                                  
                                                                                      
main = do entries ←  infentries                                                       
          forM entries logAnEntry                                                     
                                                                                      
logAnEntry entry = do                                                                 
    transport ←  hOpen ("localhost", PortNumber 9090)                                 
    let binProto = BinaryProtocol transport                                           
    let client = (binProto, binProto)                                                 
    (Client.log client) entry                                                         
    tClose transport                                                                  
    `Control.Exception.catch`                                                         
    (λ(TransportExn s t) →  print s)
--On systems with Haskell we could just generate a fuzzer like this one.

In implementing the Arbitrary instances, it was useful to make Thrift enums instances of Bounded and to improve the Enum instance. Specifically, whereas before,

[DEBUG .. ]

would throw an exception, now it behaves as expected without an exception.

I consider the patch incomplete. It's more of a starting point for a discussion at this point than a serious candidate for inclusion. If it is of interest, I'd appreciate some direction on testing it as well as style, and I'd welcome any other comments or thoughts.

Issue Links

• is part of: THRIFT-2641 Improvements to Haskell Compiler/Libraries
• is superceded by: THRIFT-2641 Improvements to Haskell Compiler/Libraries