add support for writing the 'and!' expressions and patterns (#693)

* add support for writing the 'and!' expressions and patterns

* add more tests

src/Fantomas.Tests/ComputationExpressionTests.fs

@@ -125,4 +125,58 @@ let y = async {
     |> should equal """
 let x = { 3 .. 7 }
 let y = async { return { 0 .. 1 } }
-"""
+"""
+
+[<Test>]
+let ``and! is supported`` () =
+    formatSourceString false """
+async {
+    let! x = Async.Sleep 1.
+    and! y = Async.Sleep 2.
+    return 10
+}
+"""  config
+   |> prepend newline
+   |> should equal """
+async {
+    let! x = Async.Sleep 1.
+    and! y = Async.Sleep 2.
+    return 10 }
+"""
+[<Test>]
+let ``multiple and! is supported`` () =
+    formatSourceString false """
+// Reads the values of x, y and z concurrently, then applies f to them
+parallel {
+    let! x = slowRequestX()
+    and! y = slowRequestY()
+    and! z = slowRequestZ()
+    return f x y z
+}
+"""  config
+   |> prepend newline
+   |> should equal """
+// Reads the values of x, y and z concurrently, then applies f to them
+``parallel`` {
+    let! x = slowRequestX()
+    and! y = slowRequestY()
+    and! z = slowRequestZ()
+    return f x y z }
+"""
+
+[<Test>]
+let ``and! sample number 3`` () =
+    formatSourceString false """
+observable {
+    let! a = foo
+    and! b = bar
+    return a + b
+}
+"""  config
+   |> prepend newline
+   |> should equal """
+observable {
+    let! a = foo
+    and! b = bar
+    return a + b }
+"""

src/Fantomas/CodePrinter.fs

@@ -1439,9 +1439,15 @@ and genExpr astContext synExpr =
         addParenIfAutoNln e1 (genExpr astContext) -- sprintf " <- " +> genExpr astContext e2
 
     | LetOrUseBang(isUse, p, e1, ands, e2) ->
+
+        let genAndList astContext (ands: list<SequencePointInfoForBinding * bool * bool * SynPat * SynExpr * range>) =
+            colPost sepNln sepNln
+                ands
+                (fun (_,_,_,pat,expr,_) -> !- "and! " +> genPat astContext pat -- " = " +> genExpr astContext expr)
+
         atCurrentColumn (ifElse isUse (!- "use! ") (!- "let! ")
             +> genPat astContext p -- " = " +> genExpr astContext e1 +> sepNln
-            // TODO: use ands here
+            +> genAndList astContext ands
             +> genExpr astContext e2
         )