implement suggestion #199

[pzinn]

Tentative pull. functional, with doc and test.

[DanGrayson]

The usage line here doesn't match the method being documented.

[DanGrayson]

I suggest we remove this line and the similar one in mapkeys now.

[DanGrayson]

It's hard to read with this else clause not indented the same amount as the line with "if ... then" on it.

[DanGrayson]

Let's document the effect of "continue" here.

[pzinn]

I think I got everything covered except the last one. perhaps I'll let you
explain that "continue" statement?

On Fri, Dec 5, 2014 at 1:57 AM, Daniel R. Grayson notifications@github.com
wrote:

In M2/Macaulay2/d/evaluate.d:

+export mapkeysmerge(f:Expr,o:HashTable,g:Expr):Expr := (

• x := newHashTable(o.Class,o.parent);
  

• x.beingInitialized = true;
  

• foreach bucket in o.table do (
  

• p := bucket;
  

• while true do (
  

•      if p == p.next then break;
  

•      newkey := applyEE(f,p.key);
  

•      if newkey == nullE then return buildErrorPacket("null key encountered"); -- remove soon!!!
  

•      when newkey is Error do return newkey else nothing;
  

•      h := hash(newkey);
  

•      val := lookup1(x,newkey,h);
  

•      if val != notfoundE then (
  

•         t := applyEEE(g,val,p.value);
  

•     when t is err:Error do (
  

•                  if err.message != continueMessage then return t else remove(x,newkey);
  

Let's document the effect of "continue" here.

—
Reply to this email directly or view it on GitHub
https://github.com/Macaulay2/M2/pull/200/files#r21348903.

[DanGrayson]

It looks to me like you put that line in there so that if "continue" is
executed in the body of the function
handling the collisions, then the result would be a hash table in which the
key doesn't appear. This could be used,
for example, if we are allowing hash tables to represent tallies where the
values are integers, but the value 0, denoting
absence, when encountered, results in absence.

On Thu Dec 04 2014 at 9:55:04 PM Paul Zinn-Justin notifications@github.com
wrote:

In M2/Macaulay2/d/evaluate.d:

+export mapkeysmerge(f:Expr,o:HashTable,g:Expr):Expr := (

• x := newHashTable(o.Class,o.parent);
  

• x.beingInitialized = true;
  

• foreach bucket in o.table do (
  

• p := bucket;
  

• while true do (
  

•      if p == p.next then break;
  

•      newkey := applyEE(f,p.key);
  

•      if newkey == nullE then return buildErrorPacket("null key encountered"); -- remove soon!!!
  

•      when newkey is Error do return newkey else nothing;
  

•      h := hash(newkey);
  

•      val := lookup1(x,newkey,h);
  

•      if val != notfoundE then (
  

•         t := applyEEE(g,val,p.value);
  

•     when t is err:Error do (
  

•                  if err.message != continueMessage then return t else remove(x,newkey);
  

I think I got everything covered except the last one. perhaps I'll let you
explain that "continue" statement?
… <#msg-f:1486620411913715861_>
On Fri, Dec 5, 2014 at 1:57 AM, Daniel R. Grayson <
notifications@github.com> wrote: In M2/Macaulay2/d/evaluate.d: > +export
mapkeysmerge(f:Expr,o:HashTable,g:Expr):Expr := ( > + x :=
newHashTable(o.Class,o.parent); > + x.beingInitialized = true; > + foreach
bucket in o.table do ( > + p := bucket; > + while true do ( > + if p ==
p.next then break; > + newkey := applyEE(f,p.key); > + if newkey == nullE
then return buildErrorPacket("null key encountered"); -- remove soon!!! > +
when newkey is Error do return newkey else nothing; > + h := hash(newkey);

• val := lookup1(x,newkey,h); > + if val != notfoundE then ( > + t :=
  applyEEE(g,val,p.value); > + when t is err:Error do ( > + if err.message !=
  continueMessage then return t else remove(x,newkey); Let's document the
  effect of "continue" here. — Reply to this email directly or view it on
  GitHub https://github.com/Macaulay2/M2/pull/200/files#r21348903.

—
Reply to this email directly or view it on GitHub
https://github.com/Macaulay2/M2/pull/200/files#r21354285.

[pzinn]

all right, second attempt.

[DanGrayson]

Thanks, Paul, that's a useful change!