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: glen/fostr#8
Co-Authored-By: Glen Whitney <glen@nobody@nowhere.net>
Co-Committed-By: Glen Whitney <glen@nobody@nowhere.net>

.gitignore

@@ -10,9 +10,12 @@
 
 /.polyglot.metaborg.yaml
 
+.pydevproject
+
 *.aterm
 /site
 tests/extracted/*
 tests/*.js
 tests/*.py
 tests/*.hs
+adhoc*

syntax/fostr.sdf3

@@ -18,10 +18,13 @@ context-free syntax
   Ex.Stdio    = <stdio>
   Ex.Sum      = {Ex "+"}+
   Ex.Receives = [[Ex] << [Ex]] {left}
+  Ex.Enters   = [[Ex] >> [Ex]] {left}
+  Ex          = <(<Ex>)> {bracket}
 
 context-free priorities
 
-  Ex.Sum
+  Ex.Enters
+  > Ex.Sum
   > Ex.Receives,
 
   // prevent cycle: no singletons

tests/basic.spt

@@ -71,4 +71,37 @@ stdio << 72 + 87 + 33 << 291
 /** md
 ```
 Running this program produces a nice palindromic output: "192291".
+
+And because sometimes you want to emphasize the value and propagate that
+instead of the stream, you can also write these expressions "the other way"
+with `>>`; both forms return the first argument:
+```fostr
+**/
+
+/** md */ test enters_twice [[
+(7 + 8 >> stdio + 9) >> stdio
+]]/* **/ parse to
+  Enters(Sum([Int("7"), Enters(Int("8"), Stdio()), Int("9")]), Stdio())
+/** writes
+824**/
+
+/* Extra tests not in the tour */
+
+test receive_enter [[
+stdio << (7 + 8 >> stdio + 9)
+]]/* **/ parse to
+  Receives(Stdio(), Sum([Int("7"), Enters(Int("8"), Stdio()), Int("9")]))
+/** writes
+824**/
+
+test enter_receive [[
+(7 + 8 >> stdio + 9) >> (stdio << 9 + 2)
+]]/* **/ parse to
+  Enters(Sum([Int("7"),Enters(Int("8"),Stdio()),Int("9")]),
+         Receives(Stdio(),Sum([Int("9"),Int("2")])))
+/** writes
+81124**/
+
+/** md
+```
 **/

trans/haskell.str

@@ -1,12 +1,20 @@
 module haskell
-imports libstrategolib signatures/-
+imports libstrategolib signatures/- util
 
 signature
   constructors
     TopLevel: Ex -> Ex
 
 rules
-  hs: TopLevel(x) -> $[import System.IO
+  /* Approach: Generate code from the bottom up.
+     At every node, we create a pair of the implementation and
+     necessary preamble of IO actions.
+     We concatenate preambles as we go up.
+     Finally, at the toplevel we emit the preamble before returning the
+     final value.
+   */
+
+  hs: TopLevel((c,p)) -> $[import System.IO
   data IOStream = StdIO
 
   stdio :: IO IOStream
@@ -19,21 +27,23 @@ rules
     return temp
 
   main = do
-    [<hs>x]]
+    [p]return [c]]
 
-  hs: Stdio() -> $[stdio]
+  hs: Stdio() -> ("stdio", "")
-  hs: Int(x) -> x
+  hs: Int(x) -> (x, "")
-  hs: Sum(x) -> $[sum [<hs>x]]
+  hs: Sum((c,p)) -> ($[sum [c]], p)
-  hs: Receives(x, y) -> $[[<hs>x] `receives` [<hs>y]]
+  hs: Receives((c, p), (d, s)) -> ($[[c] `receives` [d]], <conc-strings>(p,s))
-  hs: [] -> $<[]>
+  hs: Enters((c, p), (d, s)) -> <hsenter>(c,d,<conc-strings>(p,s),<newname>"fos")
-  hs: [x | xs] -> $<[<<hs>x><<hstail>xs>]>
+
+  hsenter: (x, s, p, v) -> (v, <concat-strings>[$[[p]let [v] = [x]], "\n",
+                               $[[s] `receives` [v]], "\n"])
+
+  hslist: x -> (<map(Fst); join(|", "); brack>x, <map(Snd); concat-strings>x)
+  brack: x -> $<[<x>]>
 
 strategies
   // wrap expression in a toplevel and then apply code generation
-  haskell = !TopLevel(<id>); hs
+  haskell = !TopLevel(<id>); bottomup(try(hs <+ hslist))
-
-  // translate each element of a list, prepending each with ',', and concatenate
-  hstail = foldr(!"", \ (x,y) -> $<, <<hs>x><y>> \)
 
   // Interface haskell code generation with editor services and file system
   to-haskell: (selected, _, _, path, project-path) -> (filename, result)

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: Sum(x) -> $[[x].reduce((v,w) => v+w)]
-  js: Receives(x, y) -> $[[<js>x].receives([<js>y])]
+  js: Receives(x, y) -> $[[x].receives([y])]
-  js: [] -> $<[]>
+  js: Enters(x, y) -> $[forwards([x],[y])]
-  js: [x | xs] -> $<[<<js>x><<jstail>xs>]>
+
+  jslist: x -> $<[<<join(|", ")>x>]>
 
 strategies
-  // wrap expression in a toplevel and then apply code generation
+  // wrap expression in a toplevel, then generate code from bottom up
-  javascript = !TopLevel(<id>); js
+  javascript = !TopLevel(<id>); bottomup(try(js <+ jslist))
-
-  // translate each element of a list, prepending each with ',', and concatenate
-  jstail = foldr(!"", \ (x,y) -> $<, <<js>x><y>> \)
 
   // Interface javascript code generation with editor services and file system
   to-javascript: (selected, _, _, path, project-path) -> (filename, result)

trans/python.str

@@ -1,32 +1,35 @@
 module python
-imports libstrategolib signatures/-
+imports libstrategolib signatures/- util
 
 signature
   constructors
     TopLevel: Ex -> Ex
 
 rules
+
   py: TopLevel(x) -> $[import sys
   class StdioC:
     def receives(self, v):
       print(v, file=sys.stdout, end='')
       return self
+  def forwards(data,strm):
+    strm.receives(data)
+    return data
   Stdio = StdioC()
-  [<py>x]]
+  [x]]
 
   py: Stdio() -> $[Stdio]
   py: Int(x) -> x
-  py: Sum(x) -> $[sum([<py>x])]
+  py: Sum(x) -> $[sum([x])]
-  py: Receives(x, y) -> $[[<py>x].receives([<py>y])]
+  py: Receives(x, y) -> $[[x].receives([y])]
-  py: [] -> $<[]>
+  py: Enters(x, y) -> $[forwards([x],[y])]
-  py: [x | xs] -> $<[<<py>x><<pytail>xs>]>
+
+  pylist: x -> $<[<<join(|", ")>x>]>
 
 strategies
-  // wrap expression in a toplevel and then apply code generation
-  python = !TopLevel(<id>); py
 
-  // translate each element of a list, prepending each with ',', and concatenate
+  // wrap with a toplevel, then generate code from the bottom up
-  pytail = foldr(!"", \ (x,y) -> $[, [<py>x][y]] \)
+  python = !TopLevel(<id>); bottomup(try(py <+ pylist))
 
   // Interface python code generation with editor services and file system
   to-python: (selected, _, _, path, project-path) -> (filename, result)

trans/statics.stx

@@ -10,6 +10,7 @@ rules // single-file entry point
 
   programOk(Sum(_)).
   programOk(Receives(_,_)).
+  programOk(Enters(_,_)).
 
 rules // multi-file entry point
 

trans/util.str

@@ -0,0 +1,9 @@
+module util
+imports libstrategolib
+
+rules
+  join(|infix) : [] -> ""
+  join(|infix) : [x | xs] -> $[[x][<prejoin(|infix)>xs]]
+
+  prejoin(|infix) : [] -> ""
+  prejoin(|infix) : [x | xs] -> $[[infix][x][<prejoin(|infix)>xs]]