4 ms·

I'd never seen UpSetDelayed used before (I've always used the longer /: notation), that's interesting. A silly idea I was thinking about is supporting With[

by kmill 6y ago

I'd never seen UpSetDelayed used before (I've always used the longer /: notation), that's interesting. A silly idea I was thinking about is supporting With[{x = 2}]; With[{y = 3}]; x + y for With[{x = 2}, With[{y = 3}, x + y]] to reduce nesting.

kmill 6y ago
I'm sure there are subtle bugs, but it seems to work in a simple case: SetAttributes[Have, HoldAll]; Have /: HoldPattern[CompoundExpression[x___, Have[s_Set], y__]] := CompoundExpression[x, With[{s}, CompoundExpression[y]]]; In[698]:= (Have[x = 2]; Print[x]; Have[y = 3]; Print[y]; x + y) During evaluation of In[698]:= 2 During evaluation of In[698]:= 3 Out[698]= 5
brenton_wri 6y ago
Note that you can nest within a single With: With[ {x = 2}, {y = 3}, x + y ] Though this form is not (yet) documented. Crucially, y could refer to x here. It can really help with the indentation.
- kmill 6y ago
  I use notebooks primarily -- it would be nice if syntax highlighting didn't put x+y in scary red :-) Something I've wondered: would it be possible to support With[x = 2, x + x] when there's just a single variable? It's certainly very low-priority, but it saves a few keystrokes when doing quick calculations.
  - brenton_wri 6y ago
    Yep, the proper syntax highlighting will follow when documented. There was actually a massive internal discussion in 2015 re: With[x = 2, x + x]. And With[x = 2, x + x] actually did work for a time. Unfortunately, several other ideas like With[x, x+x] and Module[x, x+x] (which was unintuitively NOT implemented as Module[{x}, x+x]) also got thrown into the conversation and things became confused, these uses were seen to be problematic, and soon the baby was thrown out with the bath water. So technically yes, With[x = 2, x + x] could work, but it is unlikely that it will ever be implemented in product.

by kmill 6y ago

kmill 6y ago

I'm sure there are subtle bugs, but it seems to work in a simple case: SetAttributes[Have, HoldAll]; Have /: HoldPattern[CompoundExpression[x___, Have[s_Set], y__]] := CompoundExpression[x, With[{s}, CompoundExpression[y]]]; In[698]:= (Have[x = 2]; Print[x]; Have[y = 3]; Print[y]; x + y) During evaluation of In[698]:= 2 During evaluation of In[698]:= 3 Out[698]= 5

brenton_wri 6y ago

Note that you can nest within a single With: With[ {x = 2}, {y = 3}, x + y ] Though this form is not (yet) documented. Crucially, y could refer to x here. It can really help with the indentation.

kmill 6y ago
I use notebooks primarily -- it would be nice if syntax highlighting didn't put x+y in scary red :-) Something I've wondered: would it be possible to support With[x = 2, x + x] when there's just a single variable? It's certainly very low-priority, but it saves a few keystrokes when doing quick calculations.
- brenton_wri 6y ago
  Yep, the proper syntax highlighting will follow when documented. There was actually a massive internal discussion in 2015 re: With[x = 2, x + x]. And With[x = 2, x + x] actually did work for a time. Unfortunately, several other ideas like With[x, x+x] and Module[x, x+x] (which was unintuitively NOT implemented as Module[{x}, x+x]) also got thrown into the conversation and things became confused, these uses were seen to be problematic, and soon the baby was thrown out with the bath water. So technically yes, With[x = 2, x + x] could work, but it is unlikely that it will ever be implemented in product.