Add proposed fluid syntax for select statement in Fluid's implementation of CSP

doc/design/csp.md

@@ -89,6 +89,55 @@ The point here is that we need a consistent way to compose types, like in C++ we
 
 ### Select
 
+In Go, the `select` statement lets a goroutine wait on multiple communication operations. A `select` blocks untill one of its cases can run, then it executes that case. It chooses one at random if multiple are ready.
+
+```go
+
+ch1 := make(chan int) 
+ch2 := make(chan int, 100)
+
+x := 0
+
+for {
+ select {
+ case ch1 <- x:
+ x := x + 1
+ case y <- ch2:
+ fmt.Println("Received on channel")
+ default:
+ fmt.Println("Default")
+ }
+ }
+
+```
+
+In Fluid, we should be able to do the same:
+
+```python
+ch1 = fluid.make_chan(dtype=INT)
+ch2 = fluid.make_chan(dtype=INT, 100)
+
+sel = fluid.select()
+
+with sel.case(ch1, 'w', X):
+ fluid.layers.increment(X)
+
+with sel.case(ch2, 'r', Y):
+ fluid.print("Received on Channel")
+
+with sel.default():
+ fluid.print("Default")
+
+```
+
+In the above code snippet, `X` and `Y` are variables. Now let us look at each of these statements one by one.
+
+- `sel.case(ch1, 'w', X)` : This specifies that we are writing to `ch1` and we want to write the integer in variable `X` to the channel. The character `w` is used here to make the syntax familar to write syntax in Python I/O.
+
+- `sel.case(ch2, 'r', Y)` : This specifies that we would like to read the result from `ch2` into variable `Y`. The character `r` is used here to make the syntax familar to read syntax in Python I/O.
+
+- `sel.default()` : This is equivalent to the default in Go `select`. If none of the channels are ready for read or write, then the fluid code in the default block will be executed.
+
 ## Example Programs
 
 ### 1. RPC between Trainers and Parameter Servers