Changeset 48786bc8 for doc/papers/general

Timestamp:

Feb 12, 2018, 1:33:42 PM (7 years ago)

Author:

Aaron Moss <a3moss@…>

Branches:

ADT, aaron-thesis, arm-eh, ast-experimental, cleanup-dtors, deferred_resn, demangler, enum, forall-pointer-decay, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, new-env, no_list, persistent-indexer, pthread-emulation, qualifiedEnum, resolv-new, with_gc

Children:

ee2938a

Parents:

43c6dc82

Message:

Added half page on choose and other switch enhancements

File:

• doc/papers/general/Paper.tex (modified) (1 diff)

doc/papers/general/Paper.tex

@@ -1044 +1044 @@
 The implicit targets of the current @continue@ and @break@, \ie the closest enclosing loop or @switch@, change as certain constructs are added or removed.
 
-\TODO{choose and fallthrough here as well?}
-
+\subsection{\texorpdfstring{Enhanced \LstKeywordStyle{switch} Statement}{Enhanced switch Statement}}
+
+\CFA also fixes a number of ergonomic defecits in the @switch@ statements of standard C. 
+C can specify a number of equivalent cases by using the default ``fall-through'' semantics of @case@ clauses, \eg @case 1: case 2: case 3:@ -- this syntax is cluttered, however, so \CFA includes a more concise list syntax, @case 1, 2, 3:@. 
+For contiguous ranges, \CFA provides an even more concise range syntax as well, @case 1~3:@; lists of ranges are also allowed in case selectors. 
+
+Forgotten @break@ statements at the end of @switch@ cases are a persistent sort of programmer error in C, and the @break@ statements themselves introduce visual clutter and an un-C-like keyword-based block delimiter. 
+\CFA addresses this error by introducing a @choose@ statement, which works identically to a @switch@ except that its default end-of-case behaviour is to break rather than to fall through for all non-empty cases. 
+Since empty cases like @case 7:@ in @case 7: case 11:@ still have fall-through semantics and explicit @break@ is still allowed at the end of a @choose@ case, many idiomatic uses of @switch@ in standard C can be converted to @choose@ statements by simply changing the keyword. 
+Where fall-through is desired for a non-empty case, it can be specified with the new @fallthrough@ statement, making @choose@ equivalently powerful to @switch@, but more concise in the common case where most non-empty cases end with a @break@ statement, as in the example below:
+
+\begin{cfa}
+choose( i ) {
+        case 2:
+                printf("even ");
+                fallthrough;
+        case 3: case 5: case 7:
+                printf("small prime\n");
+        case 4,6,8,9:
+                printf("small composite\n");
+        case 13~19:
+                printf("teen\n");
+        default:
+                printf("something else\n");
+}
+\end{cfa}
 
 \subsection{\texorpdfstring{\LstKeywordStyle{with} Clause / Statement}{with Clause / Statement}}