enso.nim: Added file operations

tests/test.nim

@@ -1,5 +1,5 @@
 import enso
-import std/[os, strformat, sugar]
+import std/[options, strformat, sugar]
 
 proc unsafe_void(str: string) =
   echo str
@@ -8,13 +8,6 @@ proc unsafe_int(str: string): int =
   echo str
   result = 1
 
-func check_file(name: string): IO[string] =
-  proc(): string =
-    if fileExists(name):
-      result = readFile(name)
-    else:
-      result = "Not found"
-
 func main() =
   run strput("Hello from Enso!")
 
@@ -32,13 +25,29 @@ func main() =
       name()
 
   let
-    nested: IO[IO[string]] = get_filename.map(check_file)
-    joined: IO[string]     = nested.join
+    nested:   IO[IO[Option[string]]] = get_filename.map(fileread)
+    joined:   IO[Option[string]]     = nested.join
+    join_opt: Option[string]         = joined()
 
-  run strput(joined())
+  if join_opt.isSome:
+    run strput(join_opt.get)
+  else:
+    run strput("joined had no data")
 
-  let flat: IO[string] = get_filename.flatmap(check_file)
-  run strput(flat())
+  let
+    flat:     IO[Option[string]] = get_filename.flatmap(fileread)
+    flat_opt: Option[string]     = flat()
+
+  if flat_opt.isSome:
+    run strput(flat_opt.get)
+  else:
+    run strput("flat had no data")
+
+  let writer: Error = run filewrite("Hello world!\n", "test.txt")
+  if writer == OK:
+    run strput("Successfully wrote test.txt!")
+  else:
+    run strput("Could not write test.txt!")
 
 when isMainModule:
   main()