Changes between Version 31 and Version 32 of PrimBool


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Timestamp:
Aug 27, 2013 9:58:22 AM (18 months ago)
Author:
simonpj
Comment:

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  • PrimBool

    v31 v32  
    8989Below is a summary of implementation details and decisions: 
    9090 
    91   * the new comparison primops return a value of type `Int#`: `1#` represents `True` and `0#` represents `False`. The `Int#` type was chosen because on Haskell it is more common to use signed Int type insetad of unsigned Word. By using `Int#` the users can easily convert unboxed result into a boxed value, without need to use `word2Int#` and `int2word#` primops. 
    92   * as a small side-task, four new logical bitwise primops have been implemented: `andI#`, `orI#`, `xorI#` and `negI#` (#7689). These operate on values of type `Int#`. Earlier we had only bitwise logical primops operating on values of type `Word#`. 
    93   * names of the existing comparison primops were changed. Operators had `$` added before `#`, others had `I` added before the `#` (this is a mnemonic denoting that this primop returns and `Int#`). Examples: 
     91  * The new comparison primops return a value of type `Int#`: `1#` represents `True` and `0#` represents `False`. The `Int#` type was chosen because on Haskell it is more common to use signed Int type insetad of unsigned Word. By using `Int#` the users can easily convert unboxed result into a boxed value, without need to use `word2Int#` and `int2word#` primops. 
     92 
     93  * Unlike C, `2#` or `-3#` don't represent a Boolean value.  More concretely, you can use `tagToEnum#` to convert one of these `Int#` values to a `Bool`, but `tagToEnum#` does no error checking, so it would be Very Very Bad to call it on `2#`. 
     94 
     95  * As a small side-task, four new logical bitwise primops have been implemented: `andI#`, `orI#`, `xorI#` and `negI#` (#7689). These operate on values of type `Int#`. Earlier we had only bitwise logical primops operating on values of type `Word#`. 
     96 
     97  * Names of the existing comparison primops were changed. Operators had `$` added before `#`, others had `I` added before the `#` (this is a mnemonic denoting that this primop returns and `Int#`). Examples: 
    9498 
    9599{{{ 
     
    102106}}} 
    103107 
    104   * a new module `GHC.PrimWrappers` was added to ghc-prim library. This module contains wrappers for comparison primops. These wrappers have names identical to removed primops and return a `Bool`. Examples: 
     108  * A new module `GHC.PrimWrappers` was added to ghc-prim library. This module contains wrappers for comparison primops. These wrappers have names identical to removed primops and return a `Bool`. Examples: 
    105109 
    106110{{{ 
     
    126130Thanks to these wrappers the change is almost backwards compatible. '''The only thing primop users need to change in their existing code to make it work again is adding import of GHC.!PrimWrappers module.''' 
    127131 
    128   * functions for comparing `Integer` type, implemented in integer-gmp and integer-simple libraries, received a similar treatment. Technically they are not primops, because they are implemented in Haskell (in case of integer-gmp also with FFI), but they pretend to be ones. There are six primops for comparing `Integer` values: 
     132  * Functions for comparing `Integer` type, implemented in integer-gmp and integer-simple libraries, received a similar treatment. Technically they are not primops, because they are implemented in Haskell (in case of integer-gmp also with FFI), but they pretend to be ones. There are six primops for comparing `Integer` values: 
    129133{{{ 
    130134eqInteger#  :: Integer -> Integer -> Int#