3182 - primitives for manipulating the file system

I don't know why this took so long to gel. I just needed to copy my
approach to screen management:

1. primitives layer (C++): simple, non-testable, non-safe operations.
2. wrappers layer (Mu): wrap operations with dependency-injected
versions that can take a fake file system.
3. scenario layer (C++): implement assume-filesystem that constructs a
fake file system.
4. scenario test layer (Mu): test out assume-filesystem in a test.

This commit implements step 1.

1 files changed, 16 insertions, 0 deletions

diff --git a/real-file.mu b/real-file.mu
new file mode 100644
index 00000000..07390696
--- /dev/null
+++ b/real-file.mu
@@ -0,0 +1,16 @@
+# example program: read a character from one file and write it to another
+# before running it, put a character into /tmp/mu-x
+
+def main [
+  local-scope
+  f:number/file <- real-open-file-for-reading [/tmp/mu-x]
+  $print [file to read from: ], f, 10/newline
+  c:character <- real-read-from-file f
+  $print [copying ], c, 10/newline
+  f <- real-close-file f
+  $print [file after closing: ], f, 10/newline
+  f <- real-open-file-for-writing [/tmp/mu-y]
+  $print [file to write to: ], f, 10/newline
+  real-write-to-file f, c
+  f <- real-close-file f
+]