feat: Add OCaml code generation

Also start using nailgun to speed up code generation.

  Resolves #6.

trans/fostr.str

@@ -6,6 +6,7 @@ imports
   pp
   outline
   analysis
+  ocaml
   haskell
   javascript
   python

trans/haskell.str

@@ -10,7 +10,7 @@ rules
         rule.
      C) We will use bottomup-para to traverse the full AST with the
         transformation from A so that we have access to the original expression
-        (and get get the Statix-associated type when we need to).
+        (and can get the Statix-associated type when we need to).
         Hence the transformation in (A) must actually take a pair of
         an (original) term and a term with value strings at each child,
         and be certain to return a value string.

trans/ocaml.str

@@ -0,0 +1,61 @@
+module ocaml
+imports libstrategolib signatures/- util signature/TYPE analysis
+
+/* Note will use bottomup-para to traverse the full AST so that
+   we have access to the original expression (and can get the
+   Statix-associated type when we need to).
+   
+   This means that every one of our local rules must take a pair
+   of an original term and a term with every child replaced by
+   its generated code.
+ */
+
+rules
+  ml: (_, TopLevel(x)) -> $[(* fostr preamble *)
+  type stream = { getS: string -> stream }
+  let rec stdio = {
+    getS = (fun s -> print_string s; stdio)
+  };;
+  (* End of preamble *)
+
+  [x]]
+
+  ml: (_, Stream())     -> $[stdio]
+  ml: (_, Int(x))       -> x
+  ml: (_, LitString(x)) -> $[{|[<un-single-quote>x]|}]
+  ml: (_, EscString(x)) -> x
+  ml: (_, Sum(x,y))     -> $[[x] + [y]]
+  ml: (Gets(_,yn), Gets(x, y))
+    -> $[([x]).getS ([<ml_str>(yn,y)])]
+  ml: (To(xn,_),   To(x, y))
+    -> $[let _fto = ([x]) in (ignore (([y]).getS ([<ml_str>(xn,"_fto")])); _fto)]
+  ml: (_, Terminate(x)) -> x
+  ml: (_, Sequence(l))  -> <ml_seq>l
+  
+  ml_seq: [x] -> x
+  ml_seq: [x | xs ] -> $[ignore ([x]);
+[<ml_seq>xs]]
+
+  /* One drawback of using paramorphism is we have to handle lists
+     explicitly:
+   */
+  ml: (_, []) -> []
+  ml: (_, [x | xs]) -> [x | xs]
+
+  /* Another drawback of using paramorphism is at the very leaves we have
+     to undouble the tuple:
+   */
+  ml: (x, x) -> x where <is-string>x
+
+  ml_str: (node, code) -> $[[<ml_string_cast>node]([code])]
+
+strategies
+
+  ml_string_cast = get-type; (?INT() < !"string_of_int" + !"")
+
+  ocaml = bottomup-para(try(ml))
+
+  // Interface ocaml code generation with editor services and file system
+  to-ocaml: (selected, _, _, path, project-path) -> (filename, result)
+    with filename := <guarantee-extension(|"ml")> path
+       ; result   := <ocaml> selected