Changeset 4136ae4

Timestamp:

Feb 22, 2018, 2:25:22 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:

d2887f7

Parents:

4ada74e

Message:

Minor cleanup on _Generic, zero_t

File:

• doc/papers/general/Paper.tex (modified) (4 diffs)

doc/papers/general/Paper.tex

@@ -41 +41 @@
 
 \newcommand{\Textbf}[2][red]{{\color{#1}{\textbf{#2}}}}
-\newcommand{\TODO}[1]{\textbf{TODO}: {\itshape #1}} % TODO included
-%\newcommand{\TODO}[1]{} % TODO elided
+%\newcommand{\TODO}[1]{\textbf{TODO}: {\itshape #1}} % TODO included
+\newcommand{\TODO}[1]{} % TODO elided
 
 % Default underscore is too low and wide. Cannot use lstlisting "literate" as replacing underscore
@@ -260 +260 @@
 \Celeven did add @_Generic@ expressions, which can be used in preprocessor macros to provide a form of ad-hoc polymorphism; however, this polymorphism is both functionally and ergonomically inferior to \CFA name overloading. 
 The macro wrapping the generic expression imposes some limitations; as an example, it could not implement the example above, because the variables @max@ would collide with the functions @max@. 
-Ergonomic limitations of @_Generic@ include the necessity to put a fixed list of supported types in a single place and manually dispatch to appropriate overloads, as well as possible namespace pollution from the functions dispatched to, which must all have distinct names.
+Ergonomic limitations of @_Generic@ include the necessity to put a fixed list of supported types in a single place and manually dispatch to appropriate overloads, as well as possible namespace pollution from the functions dispatched to, which must all have distinct names. 
+Though name-overloading removes a major use-case for @_Generic@ expressions, \CFA does implement @_Generic@ for backwards-compatibility purposes. \TODO{actually implement that}
 
 % http://fanf.livejournal.com/144696.html
@@ -1984 +1985 @@
 
 In C, @0@ has the special property that it is the only ``false'' value; by the standard, any value which compares equal to @0@ is false, while any value that compares unequal to @0@ is true. 
-As such, an expression @x@ in any boolean context (such as the condition of an @if@ or @while@ statement, or the arguments to an @&&@, @||@, or ternary operator) can be rewritten as @x != 0@ without changing its semantics.
+As such, an expression @x@ in any boolean context (such as the condition of an @if@ or @while@ statement, or the arguments to @&&@, @||@, or @?:@) can be rewritten as @x != 0@ without changing its semantics.
 The operator overloading feature of \CFA provides a natural means to implement this truth value comparison for arbitrary types, but the C type system is not precise enough to distinguish an equality comparison with @0@ from an equality comparison with an arbitrary integer or pointer. 
-To provide this precision, \CFA introduces a new type @zero_t@ as type type of literal @0@ (somewhat analagous to @nullptr_t@ and @nullptr@ in \CCeleven); @zero_t@ can only take the value @0@, but has implicit conversions to the integer and pointer types so that standard C code involving @0@ continues to work properly. 
+To provide this precision, \CFA introduces a new type @zero_t@ as type type of literal @0@ (somewhat analagous to @nullptr_t@ and @nullptr@ in \CCeleven); @zero_t@ can only take the value @0@, but has implicit conversions to the integer and pointer types so that C code involving @0@ continues to work properly. 
 With this addition, the \CFA compiler rewrites @if (x)@ and similar expressions to @if ((x) != 0)@ or the appropriate analogue, and any type @T@ can be made ``truthy'' by defining an operator overload @int ?!=?(T, zero_t)@.
 \CC makes types truthy by adding a conversion to @bool@; prior to the addition of explicit cast operators in \CCeleven this approach had the pitfall of making truthy types transitively convertable to any numeric type; our design for \CFA avoids this issue.
@@ -1993 +1994 @@
 The addition of @one_t@ allows generic algorithms to handle the unit value uniformly for types where that is meaningful. 
 \TODO{Make this sentence true} In particular, polymorphic functions in the \CFA prelude define @++x@ and @x++@ in terms of @x += 1@, allowing users to idiomatically define all forms of increment for a type @T@ by defining the single function @T & ?+=(T &, one_t)@; analogous overloads for the decrement operators are present as well.
-
 
 \subsection{Integral Suffixes}