Script to redeploy testlib.sml to all exercises on changes. (#206)

* Script to redeploy testlib.sml to all exercises on changes.

The directory name `sml-bin` makes the most sense to me for these sml
"scripts".  Adding them to the makefile also makes it even easier to
use these than it is when using "#! /usr/bin/env -S poly --script" as
a shebang line.  Consequently this should be portable to any Windows
system that has GNU make installed, so it is probably better than the
shebang.  In the code I used the path library to help make things OS
portable, but I haven't ever used SML on Windows, so it is untested
for that enironment.

* Change file perms to 664 for sml-bin/redeploy-testlib.sml

I had set it to 775 when it had a shebang and lived in `bin`.  Trying
to execute it will fail, so it shouldn't be executable.

* Make redeploy-testlib phone as well.

* Use qualified names.

I shouldn't have combined to actions but I did.  I removed all
unnecessary semicolons while refactoring to use qualified names.
Sorry.

* Format redeploy-testlib.sml like teslib.sml

I also found and removed two more unnecessary semicolons.

* Include testlib sync policy in the README.

I wrote a brief note about keeping testlib.sml in sync for all
exercises in the track, and I mentioned 'make redeploy-testlib' as the
provided tool for handling this requirement.

I did not elaborate on a policy, because we still don't really have
one.  Further work related to #110 should result in a clear policy,
and at that point the README.md might need some more updating.

* Formatting, names, parentheses.

* Update README.md

Co-authored-by: Victor Goff <keeperotphones@gmail.com>

* Add spaces inside tuples.

* Use scripts directory instead of sml-bin.

* Add a documenting comment to redeploy-testlib.sml.

Initially, I thought it must be clear enough from the title/name of
the script itself, but on further reflection, a documenting comment
might help a non-native english speaker avoid the difficulties of
ambiguity.

Co-authored-by: Victor Goff <keeperotphones@gmail.com>

Makefile

@@ -15,4 +15,7 @@ test-%:
 	@cd ./exercises/practice/$(exercise) && cat test.sml | sed 's/$(exercise).sml/.meta\/example.sml/' | poly -q
 	@echo
 
-.PHONY: test
+redeploy-testlib:
+	poly --script scripts/redeploy-testlib.sml
+
+.PHONY: test redeploy-testlib

README.md

@@ -30,7 +30,11 @@ Every exercise must have at least these files:
 
 ### `testlib.sml`
 
-This helper has this structures:
+The copy of `testlib.sml` for each exercise should be in sync with `lib/testlib.sml`.
+`make redeploy-testlib` is provided for synchronizing all exercises with `lib/testlib.sml`
+when it is updated.
+
+This helper has these structures:
 
 ```sml
 structure Expect:

scripts/redeploy-testlib.sml

@@ -0,0 +1,55 @@
+(* Re-deploy lib/testlib.sml on changes.
+ *
+ * When lib.testlib.sml is changed it should be updated for all exercises.
+ * Use this "script" a la `make redeploy-testlib`.
+ *)
+
+structure Path =  OS.Path
+structure File =  OS.FileSys
+
+fun printLn x = print (x ^ "\n")
+
+fun fileExists x = File.access (x, [])
+
+fun testLibName base slug =
+  Path.joinDirFile
+    {
+      dir = Path.concat (base, slug),
+      file = "testlib.sml"
+    }
+
+fun dirList dirname =
+  let
+    fun go d xs =
+      case File.readDir d of
+          SOME x => go d (x::xs)
+        | NONE   => (File.closeDir d; xs)
+  in
+    go (File.openDir dirname) []
+  end
+
+fun fileBytes path =
+  let
+    val instream = BinIO.openIn path
+    val bytes = BinIO.inputAll instream
+  in
+    BinIO.closeIn instream; bytes
+  end
+
+fun writeFileBytes bytes path =
+  let
+    val out = BinIO.openOut path
+  in
+    BinIO.output (out, bytes);
+    BinIO.closeOut out
+  end
+
+fun relUnixPathToAbs x = Path.concat (File.getDir (), Path.fromUnixPath x)
+
+val _ =
+  let
+    val practice = relUnixPathToAbs "exercises/practice"
+    val testLib = fileBytes "lib/testlib.sml"
+  in
+    List.app (writeFileBytes testLib o testLibName practice) (dirList practice)
+  end