Allow variable declaration in run result

[schorg]

I would like to write this:

let summary = run Controller()

But the compiler wants me to separate this like that:

var summary: Summary 
summary = run Controller()

Any chance to align this with function invocations?

This feature request was originally proposed by @frameworklabs

[schorg]

run is a statement and and cannot occur in a right-hand-side expression.

To emphasize the statement character we propose to use

run let summary = Controller()

This will also break the old syntax, which changes to:

var summary: Summary
run summary = Controller()

This proposal is the result of a discussion on slack: https://blech-lang.slack.com/archives/CE0K9FFB6/p1588692639029400

[schorg]

Some remarks: We would allow:

run let s = Ctrl()
run var s = Ctrl()

These are fresh memory locations which act as local variables. They also occur in the following statements

for let i: nat8 = 1, 10 do ... end
if let payload = anEvent then ... end // event presence test and unpacking
await let payload = anEvent // await event presence and unpack payload
emit let evt = payload //  one-shot event
emit let evt: event // one-shot event without payload

Everywhere var is also possible.

We do not allow the combination of run and emit statement.

run emit let evt = CtrlReturnsPayload()

In this rare case you need two statements

run let payload = CtrlReturnsPayload()
emit let evt = payload 

For the fresh location we do not allow extern locations and references.

extern var, extern let
let ref, var ref
extern let ref, extern var ref

All of this will be encoded into the grammar.

[schorg]

One more thing: Blech should allow to directly return with the result of a sub-activity. To combine the run and return statement, we will write:

return run Ctrl()

Instead of

run let summary = Ctrl()
return summary

In puts the emphasis on return and not the other way round run return Ctrl().

[FriedrichGretz]

I believe both the in-place declaration of the receiver as well as the return of a run result are completed on the develop branch. Provided we document this feature properly, it can be released into master.

[FriedrichGretz]

Fixed with Release 0.6.0