Some changes, and some examples to start with for error propagation

1 files changed, 31 insertions, 2 deletions

diff --git a/language_description.md b/language_description.md
index 1a50c37..fd54e50 100644
--- a/language_description.md
+++ b/language_description.md
@@ -49,7 +49,7 @@ If something causes `malloc` to be uncallable, e.g. if there is insufficient
 stack space to hold its local variables, it simply returns a meaningless
 pointer and a non-nil error value. Note that although we return "`0`" in the
 example code above, the zero pointer is not guaranteed to be an invalid pointer
-in $e^2$.
+in `e²`.
 
 Other functions may have different methods of failure. Some might return an
 error, so it might be natural to set their error return value to something like
@@ -129,6 +129,35 @@ try {
 The overflow is caught if and only if it is not handled at the point of the
 operation and has not been handled at an inner `on_overflow`.
 
+## Error propagation
+
+```e2
+(int x, char y) do_stuff() {
+	...
+	return 0, 1; // Not an error
+	...
+	return var, 2; // Also not an error
+	...
+	return 0, 5; // Some error
+	...
+	return -5, 3; // Some other error
+} on_fail {
+	return 0, 9; // Another error
+} error {
+	// Consider it an error if (and only if) the 2nd return value is >= 3
+	return y >= 3;
+}
+```
+
+```e2
+int f() {
+	// If do_stuff() errored, return ENOCONN
+	int a, char b = do_stuff()!(ENOTCONN);
+
+	return a - b;
+}
+```
+
 ## Other non-trivial differences from C
 
 1.  Instead of `errno`, we use multiple return values to indicate errors where
@@ -144,6 +173,6 @@ operation and has not been handled at an inner `on_overflow`.
 7.  There is no special null pointer.
 8.  No implicit integer promotion.
 9.  Void pointers of varying depth (such as `void **`) can be implicitly casted
-    to pointers of the same or deeper depth (such as `void **` -> `int ***`,
+    to or from pointers of the same or deeper depth (such as `void **` -> `int ***`,
     but not `void **` -> `int *`).
 10. There is language-level support for tagged unions.