Reconfigurable pretty-printing in GHCi

Phil Wadler wants to control the pretty-printer used to display output in GHCi. Something: adding a flag

  -pretty <function-name>

The supplied function will typically have type (C a => a -> String) for some class C. Using Razvan's libary, he could declare

  :set -pretty GenericPretty.pretty

for example.

Since this is GHCi-specific, one could use a new GHCi command instead:

:pretty GenericPretty.pretty

The latter design would presumably look up GenericPretty.pretty in the current context, and bleat if not found. The version with a flag might do that each time the pretty printer was used, which is arguably less efficient and (more important) more confusing. Personally I think I prefer the :pretty command best. (I'm not fussy about the name.)

Trac metadata

Trac field	Value
Version	7.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	wadler@inf.ed.ac.uk
Operating system
Architecture