Change log

Unreleased

gopter.GenParameters now has a CloneWithSeed(seed int64) function to temparary copies to create rerunable sections of code.
Added gopter.Gen.MapResult for power-user mappings
Added gopter.DeriveGen to derive a generator and it's shrinker from a bi-directional mapping (gopter.BiMapper)

Refactored commands package under the hood to allow the use of mutable state. Re-runability of commands is provided by invoking the commands.GenInitialState generator with the same gopter.GenParameters. Of course commands.GenInitialState is supposed to create the same state for the same parameters every time.
Fixed a bug in commands that might lead to shrinked command sequences not satisfying the precondtions.
commands.Command.PostCondition was called with the state before running the command. It makes much more sense to first do commands.Command.NextState and then commands.Command.PostCondition
commands.Commands.NewSystemUnderTest now takes has an argument initialState commands.State to allow implementators to create/bootstrap a system under test based on an arbitrary initial state. So far examples were just using a constant initial state ... which is a bit boring.
Fixed: Actually use commands.Commands.InitialPreCondition as sieve for commands.Commands.GenInitialState

Gen.Map and Shrink.Map now accept interface{} instead of func (interface{}) interface{}

This allows cleaner mapping functions without type conversion. E.g. instead of

gen.AnyString().Map(function (v interface{}) interface{} {
   return strings.ToUpper(v.(string))
})

you can (and should) now write

gen.AnyString().Map(function (v string) string {
   return strings.ToUpper(v)
})

Correspondingly Gen.SuchThat now also ccept interface{} instead of func (interface{}) bool

This allows cleaner sieve functions without type conversion. E.g. instead of

gen.AnyString().SuchThat(function (v interface{}) bool {
   return HasPrefix(v.(string), "P")
})

you can (and should) now write

gen.AnyString().SuchThat(function (v string) bool {
   return HasPrefix(v, "P")
})

Gen.FlatMap now has a second parameter resultType reflect.Type defining the result type of the mapped generator
Reason for these changes: The original Map and FlatMap had a recurring issue with empty results. If the original generator created an empty result there was no clean way to determine the result type of the mapped generator. The new version fixes this by extracting the return type of the mapping functions.