Add toExternalString(MutableMatrix)

[d-torrance]

Before

i1 : toExternalString mutableMatrix {{1, 2}, {3, 4}}
stdio:1:1:(3): error: can't convert local symbol or invisible global symbol 'RawMutableMatrix' to external string
null: here is the first use of 'RawMutableMatrix'

After

i1 : toExternalString mutableMatrix {{1, 2}, {3, 4}}

o1 = mutableMatrix(map(ZZ^2,ZZ^2,{{1, 2}, {3, 4}}))

[d-torrance]

I've re-written this so that toExternalString for mutable hash tables, lists, and matrices all call the same function that uses synonym in the error message.

Before

i1 : toExternalString new SelfInitializingType of HashTable
stdio:1:1:(3): error: anonymous type cannot be converted to external string

i2 : toExternalString mutableMatrix {{0}}
stdio:2:1:(3): error: can't convert local symbol or invisible global symbol 'RawMutableMatrix' to external string
null: here is the first use of 'RawMutableMatrix'

After

i1 : toExternalString new SelfInitializingType of HashTable
stdio:1:1:(3): error: anonymous self initializing type cannot be converted to external string

i2 : toExternalString mutableMatrix {{0}}
stdio:2:1:(3): error: anonymous mutable matrix cannot be converted to external string

[mahrud]

Looks good. Mind if I send in a couple of commits, clearing up unnecessary toExternalString methods for different types of rings?

[d-torrance]

Go for it!

[mahrud]

Now we have:

i1 : select(methods toExternalString, m -> ancestor(MutableHashTable, m#1))

o1 = {0 => (toExternalString, Monoid)          }
     {1 => (toExternalString, MutableHashTable)}
     {2 => (toExternalString, Ring)            }
     {3 => (toExternalString, Variety)         }

But among these, the mutable hash table one is just an error:

i3 : code o1#1

o3 = -- code for method: toExternalString(MutableHashTable)
     ../../Macaulay2/m2/nets.m2:73:39-76:43: --source code:
     toExternalString MutableList      := s -> (
         if hasAttribute(s,ReverseDictionary)
         then toString getAttribute(s,ReverseDictionary)
         else error("anonymous ", synonym class s,

And the other three are convenient exceptions because you can make a matrix, list, or hash table immutable, but you can't turn a monoid, ring, or variety immutable.

Tangentially:

1. typing code 1 above gives the code for (toExternalString, BasicList), because select didn't update the cached methods list. Maybe we should have the after print of NumberedVerticalList automatically update a unified variable "lastlist", which can be used by all help, code, etc?
2. the last line of (toExternalString, MutableList) is dropped for some reason.

[mahrud]

I'm happy with this. If the changes I added are okay, feel free to merge!

[mahrud]

Related: have you seen #1026?