Changes in / [89e1b16:1e4f05e]

File:

• doc/generic_types/generic_types.tex (modified) (2 diffs)

doc/generic_types/generic_types.tex

@@ -139 +139 @@
 \begin{lstlisting}
 forall(otype T)
-T identity(T x) {
+T identity(T x) {is_
     return x;
 }
@@ -294 +294 @@
 Since @pair(T*, T*)@ is a concrete type, there are no added implicit parameters to @lexcmp@, so the code generated by \CFA{} will be effectively identical to a version of this written in standard C using @void*@, yet the \CFA{} version will be type-checked to ensure that the fields of both pairs and the arguments to the comparison function match in type.
 
-Another useful pattern enabled by re-used dtype-static type instantiations is zero-cost ``tag'' structs. Sometimes a particular bit of information is only useful for type-checking, and can be omitted at runtime. Tag structs can be used to provide this information to the compiler without further runtime overhead, as in the following example:
-\begin{lstlisting}
-forall(dtype Unit) struct scalar { unsigned long value; };
-
-struct metres {};
-struct litres {};
-
-forall(dtype U)
-scalar(U) ?+?(scalar(U) a, scalar(U) b) {
-        return (scalar(U)){ a.value + b.value };
-}
-
-scalar(metres) half_marathon = { 21093 };
-scalar(litres) swimming_pool = { 2500000 };
-
-scalar(metres) marathon = half_marathon + half_marathon;
-scalar(litres) two_pools = swimming_pool + swimming_pool;
-marathon + swimming_pool; // ERRORv -- caught by compiler
-\end{lstlisting}
-@scalar@ is a dtype-static type, so all uses of it will use a single struct definition, containing only a single @unsigned long@, and can share the same implementations of common routines like @?+?@ -- these implementations may even be separately compiled, unlike \CC{} template functions. However, the \CFA{} type-checker will ensure that matching types are used by all calls to @?+?@, preventing nonsensical computations like adding the length of a marathon to the volume of an olympic pool.
+\TODO{} The second is zero-cost ``tag'' structs.
 
 \section{Tuples}