feat: Implement enters operator >> (#8)

Also adds parenthesization of fostr expressions.
  Recasts code generation in terms of bottomup processing
  of a local strategy.

  Resolves #1.

Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: #8
Co-Authored-By: Glen Whitney <glen@nobody@nowhere.net>
Co-Committed-By: Glen Whitney <glen@nobody@nowhere.net>

trans/javascript.str

@@ -1,5 +1,5 @@
 module javascript
-imports libstrategolib signatures/-
+imports libstrategolib signatures/- util
 
 signature
   constructors
@@ -7,23 +7,25 @@ signature
 
 rules
   js: TopLevel(x) -> $[const Stdio = {
-    receives: v => { process.stdout.write(String(v)); return Stdio; }
+    receives: v => { process.stdout.write(String(v)); return Stdio; },
   }
-  [<js>x]]
+  function forwards(data, strm) {
+    strm.receives(data);
+    return data;
+  }
+  [x]]
 
   js: Stdio() -> $[Stdio]
   js: Int(x) -> x
-  js: Sum(x) -> $[[<js>x].reduce((v,w) => v+w)]
-  js: Receives(x, y) -> $[[<js>x].receives([<js>y])]
-  js: [] -> $<[]>
-  js: [x | xs] -> $<[<<js>x><<jstail>xs>]>
+  js: Sum(x) -> $[[x].reduce((v,w) => v+w)]
+  js: Receives(x, y) -> $[[x].receives([y])]
+  js: Enters(x, y) -> $[forwards([x],[y])]
+
+  jslist: x -> $<[<<join(|", ")>x>]>
 
 strategies
-  // wrap expression in a toplevel and then apply code generation
-  javascript = !TopLevel(<id>); js
-
-  // translate each element of a list, prepending each with ',', and concatenate
-  jstail = foldr(!"", \ (x,y) -> $<, <<js>x><y>> \)
+  // wrap expression in a toplevel, then generate code from bottom up
+  javascript = !TopLevel(<id>); bottomup(try(js <+ jslist))
 
   // Interface javascript code generation with editor services and file system
   to-javascript: (selected, _, _, path, project-path) -> (filename, result)