feat: Allow expressions to be terminated/sequenced by ;

Note that ultimately a terminated sequence may have
   a slightly different semantics (applying streams
   to `_|_`, most likely) but for now they don't.

tests/basic.spt

@@ -14,8 +14,8 @@ that writes the sum of the ASCII codes for 'H', 'W', and '!' to standard output:
 
 /** md */ test emit_sum [[
 stream << 72 + 87 + 33
-]]/* **/ parse to TopLevel(Gets(Stream(),
-                                Sum(Sum(Int("72"), Int("87")), Int("33"))))
+]] /* **/
+parse to TopLevel(Gets(Stream(), Sum(Sum(Int("72"), Int("87")), Int("33"))))
 /** writes
 192**/
 
@@ -59,7 +59,8 @@ is also left-associative, so that way we can chain insertions into a stream:
 
 /** md */ test emit_twice [[
 stream << 72 + 87 + 33 << 291
-]]/* **/ parse to TopLevel(
+]] /* **/
+parse to TopLevel(
   Gets(Gets(Stream(), Sum(Sum(Int("72"), Int("87")), Int("33"))), Int("291")))
 /** writes
 192291**/
@@ -76,7 +77,8 @@ with `>>`; both forms return the first argument, so the following writes "824":
 
 /** md */ test enters_twice [[
 (7 + 8 >> stream + 9) >> stream
-]]/* **/ parse to TopLevel(
+]] /* **/
+parse to TopLevel(
   To(Sum(Sum(Int("7"), To(Int("8"), Stream())), Int("9")), Stream()))
 /** writes
 824**/
@@ -96,7 +98,8 @@ stream <<
   7
   + 8 >> stream
   + 9
-]]/* **/ parse to TopLevel(
+]] /* **/
+parse to TopLevel(
   Gets(Stream(), Sum(Sum(Int("7"), To(Int("8"), Stream())), Int("9"))))
 /** writes
 824**/
@@ -107,15 +110,17 @@ stream <<
 ```fostr
 **/
 
-/** md */ test enter_receive_bad_break [[
+/** md */ test enter_receive_bad_continuation [[
 (7 + 8 >> stream + 9)
 >> (stream << 9 + 2)
-]] /* **/ parse fails
+]] /* **/
+parse fails
 
 /* Extra tests not in the tour */
 test enter_receive [[
 (7 + 8 >> stream + 9) >> (stream << 9 + 2)
-]]/* **/ parse to TopLevel(
+]] /* **/
+parse to TopLevel(
   To(Sum(Sum(Int("7"),To(Int("8"),Stream())),Int("9")),
      Gets(Stream(),Sum(Int("9"),Int("2")))))
 /** writes
@@ -135,18 +140,20 @@ lines are evaluated in sequence. For example, the program
     + 96
   99 + 12 >>
           stream
-]] /* **/ parse to TopLevel( Sequence(
-    [ Gets(Stream(), Sum(Int("72"), Int("87")))
-    , Gets(Stream(), Sum(Int("88"), Int("96")))
-    , Sum(Int("99"), To(Int("12"), Stream()))]))
+]] /* **/
+parse to TopLevel(Sequence([
+  Gets(Stream(), Sum(Int("72"), Int("87"))),
+  Gets(Stream(), Sum(Int("88"), Int("96"))),
+  Sum(Int("99"), To(Int("12"), Stream()))
+]))
 /** writes
 15918412**/
 
 /** md
 ```
 
-will write 15918412. fostr enforces that successive expressions in sequence
-must line up at the left, i.e., the following will not parse:
+will write 15918412. The fostr parser enforces that successive expressions
+in sequence align at the left; e.g., the following fails to parse:
 
 ```fostr
 **/
@@ -156,8 +163,61 @@ must line up at the left, i.e., the following will not parse:
 stream << 88
     + 96
   99 + 12 >> stream
-]] /* **/ parse fails
+]] /* **/
+parse fails
+
+/** md
+```
+
+Note you can optionally terminate an expression in a sequence with a semicolon,
+and you may place multiple expressions on a single line if the earlier one(s)
+are so terminated. So the following is OK:
+
+```fostr
+**/
+
+/** md */ test emit_several [[
+  stream << 1 + 2; 3 >> stream
+  (4 + 5) >> stream; stream << 6;
+  stream << 7
+  stream << 8
+    + (9+10);
+  11 + 12 >> stream; 13 >> stream
+                        >> stream
+]] /* **/
+parse to TopLevel(Sequence([
+  ISequence(Prior([Terminate(Gets(Stream(), Sum(Int("1"), Int("2"))))]),
+            To(Int("3"), Stream())),
+  ISequence(Prior([Terminate(To(Sum(Int("4"), Int("5")), Stream()))]),
+            Terminate(Gets(Stream(), Int("6")))),
+  Gets(Stream(), Int("7")),
+  Terminate(Gets(Stream(), Sum(Int("8"), Sum(Int("9"), Int("10"))))),
+  ISequence(Prior([Terminate(Sum(Int("11"), To(Int("12"), Stream())))]),
+            To(To(Int("13"), Stream()), Stream()))
+]))
+/** writes
+3396727121313**/
 
 /** md
 ```
 **/
+
+test emit_several_desugar [[
+  stream << 1 + 2; 3 >> stream
+  (4 + 5) >> stream; stream << 6;
+  stream << 7
+  stream << 8
+    + (9+10);
+  11 + 12 >> stream; 13 >> stream
+                        >> stream
+]] /* don't test */
+run desugar-fostr to TopLevel(Sequence([
+  Terminate(Gets(Stream(), Sum(Int("1"), Int("2")))),
+  To(Int("3"), Stream()),
+  Terminate(To(Sum(Int("4"), Int("5")), Stream())),
+  Terminate(Gets(Stream(), Int("6"))),
+  Gets(Stream(), Int("7")),
+  Terminate(Gets(Stream(), Sum(Int("8"), Sum(Int("9"), Int("10"))))),
+  Terminate(Sum(Int("11"), To(Int("12"), Stream()))),
+  To(To(Int("13"), Stream()), Stream())
+]))

tests/emit_several.fos

@@ -0,0 +1,7 @@
+stream << 1 + 2; 3 >> stream
+(4 + 5) >> stream; stream << 6;
+stream << 7 
+stream << 8
+  + (9+10);
+11 + 12 >> stream; 13 >> stream
+                      >> stream