• David Himmelstrup's avatar
    Add several new record features · 2eb04ca0
    David Himmelstrup authored
    1. Record disambiguation (-fdisambiguate-record-fields)
    
    In record construction and pattern matching (although not
    in record updates) it is clear which field name is intended
    even if there are several in scope.  This extension uses
    the constructor to disambiguate.  Thus
    	C { x=3 }
    uses the 'x' field from constructor C (assuming there is one)
    even if there are many x's in scope.
    
    
    2. Record punning (-frecord-puns)
    
    In a record construction or pattern match or update you can 
    omit the "=" part, thus
    	C { x, y }
    This is just syntactic sugar for
    	C { x=x, y=y }
    
    
    3.  Dot-dot notation for records (-frecord-dot-dot)
    
    In record construction or pattern match (but not update) 
    you can use ".." to mean "all the remaining fields".  So
    
    	C { x=v, .. }
    
    means to fill in the remaining fields to give
    
    	C { x=v, y=y }
    
    (assuming C has fields x and y).  This might reasonably
    considered very dodgy stuff.  For pattern-matching it brings
    into scope a bunch of things that are not explictly mentioned;
    and in record construction it just picks whatver 'y' is in
    scope for the 'y' field.   Still, Lennart Augustsson really
    wants it, and it's a feature that is extremely easy to explain.
    
    
    Implementation
    ~~~~~~~~~~~~~~
    I thought of using the "parent" field in the GlobalRdrEnv, but
    that's really used for import/export and just isn't right for this.
    For example, for import/export a field is a subordinate of the *type
    constructor* whereas here we need to know what fields belong to a
    particular *data* constructor.
    
    The main thing is that we need to map a data constructor to its
    fields, and we need to do so in the renamer.   For imported modules
    it's easy: just look in the imported TypeEnv.  For the module being
    compiled, we make a new field tcg_field_env in the TcGblEnv.
    The important functions are
    	RnEnv.lookupRecordBndr
    	RnEnv.lookupConstructorFields
    
    There is still a significant infelicity in the way the renamer
    works on patterns, which I'll tackle next.
    
    
    I also did quite a bit of refactoring in the representation of
    record fields (mainly in HsPat).***END OF DESCRIPTION***
    
    Place the long patch description above the ***END OF DESCRIPTION*** marker.
    The first line of this file will be the patch name.
    
    
    This patch contains the following changes:
    
    M ./compiler/deSugar/Check.lhs -3 +5
    M ./compiler/deSugar/Coverage.lhs -6 +7
    M ./compiler/deSugar/DsExpr.lhs -6 +13
    M ./compiler/deSugar/DsMeta.hs -8 +8
    M ./compiler/deSugar/DsUtils.lhs -1 +1
    M ./compiler/deSugar/MatchCon.lhs -2 +2
    M ./compiler/hsSyn/Convert.lhs -3 +3
    M ./compiler/hsSyn/HsDecls.lhs -9 +25
    M ./compiler/hsSyn/HsExpr.lhs -13 +3
    M ./compiler/hsSyn/HsPat.lhs -25 +63
    M ./compiler/hsSyn/HsUtils.lhs -3 +3
    M ./compiler/main/DynFlags.hs +6
    M ./compiler/parser/Parser.y.pp -13 +17
    M ./compiler/parser/RdrHsSyn.lhs -16 +18
    M ./compiler/rename/RnBinds.lhs -2 +2
    M ./compiler/rename/RnEnv.lhs -22 +82
    M ./compiler/rename/RnExpr.lhs -34 +12
    M ./compiler/rename/RnHsSyn.lhs -3 +2
    M ./compiler/rename/RnSource.lhs -50 +78
    M ./compiler/rename/RnTypes.lhs -50 +84
    M ./compiler/typecheck/TcExpr.lhs -18 +18
    M ./compiler/typecheck/TcHsSyn.lhs -20 +21
    M ./compiler/typecheck/TcPat.lhs -8 +6
    M ./compiler/typecheck/TcRnMonad.lhs -6 +15
    M ./compiler/typecheck/TcRnTypes.lhs -2 +11
    M ./compiler/typecheck/TcTyClsDecls.lhs -3 +4
    M ./docs/users_guide/flags.xml +7
    M ./docs/users_guide/glasgow_exts.xml +42
    2eb04ca0
DsMeta.hs 64.2 KB