| 1 | % ======================================================================
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| 2 | % ======================================================================
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| 3 | \chapter{Introduction to \CFA}\label{s:cfa}
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| 4 | % ======================================================================
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| 5 | % ======================================================================
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| 6 |
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| 7 | \section{Overview}
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| 8 | The following serves as an introduction to \CFA.
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| 9 | \CFA is a layer over C, is transpiled\footnote{Source to source translator.} to C, and is largely considered to be an extension of C.
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| 10 | Beyond C, it adds productivity features, extended libraries, an advanced type-system, and many control-flow/concurrency constructions.
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| 11 | However, \CFA stays true to the C programming style, with most code revolving around @struct@'s and routines, and respects the same rules as C.
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| 12 | \CFA is not object oriented as it has no notion of @this@ (receiver) and no structures with methods, but supports some object oriented ideas including constructors, destructors, and limited nominal inheritance.
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| 13 | While \CFA is rich with interesting features, only the subset pertinent to this work is discussed.
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| 14 |
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| 15 | \section{References}
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| 16 | References in \CFA are similar to references in \CC; however \CFA references are \emph{rebindable}, and support multi-level referencing.
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| 17 | References in \CFA are a layer of syntactic sugar over pointers to reduce the number of ref/deref operations needed with pointer usage.
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| 18 | Another difference is the use of @0p@ instead of C's @NULL@ or \CC's @nullptr@.
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| 19 | Examples of references are shown in \VRef[Listing]{l:cfa_ref}.
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| 20 |
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| 21 | \begin{cfa}[caption={Example of \CFA references},label={l:cfa_ref}]
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| 22 | int i = 2;
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| 23 | int & ref_i = i; $\C{// declare ref to i}$
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| 24 | int * ptr_i = &i; $\C{// ptr to i}$
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| 25 |
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| 26 | // address of ref_i is the same as address of i
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| 27 | assert( &ref_i == ptr_i );
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| 28 |
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| 29 | int && ref_ref_i = ref_i; $\C{// can have a ref to a ref}$
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| 30 | ref_i = 3; $\C{// set i to 3}$
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| 31 | int new_i = 4;
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| 32 |
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| 33 | // syntax to rebind ref_i (must cancel implicit deref)
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| 34 | &ref_i = &new_i; $\C{// (\&*)ref\_i = \&new\_i; (sets underlying ptr)}$
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| 35 | \end{cfa}
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| 36 |
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| 37 |
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| 38 | \section{Overloading}\label{s:Overloading}
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| 39 | \CFA routines can be overloaded on parameter type, number of parameters, and \emph{return type}.
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| 40 | Variables can also be overloaded on type, meaning that two variables can have the same name so long as they have different types.
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| 41 | A routine or variable is disambiguated at each usage site via its type and surrounding expression context.
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| 42 | A cast is used to disambiguate any conflicting usage.
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| 43 | Examples of overloading are shown in \VRef[Listing]{l:cfa_overload}.
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| 44 |
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| 45 | \begin{cfa}[caption={Example of \CFA overloading},label={l:cfa_overload}]
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| 46 | int foo() { sout | "A"; return 0;}
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| 47 | int foo( int bar ) { sout | "B"; return 1; }
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| 48 | int foo( double bar ) { sout | "C"; return 2; }
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| 49 | double foo( double bar ) { sout | "D"; return 3; }
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| 50 | void foo( double bar ) { sout | bar; }
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| 51 |
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| 52 | int main() {
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| 53 | foo(); $\C{// prints A}$
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| 54 | foo( 0 ); $\C{// prints B}$
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| 55 | int foo = foo( 0.0 ); $\C{// prints C}$
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| 56 | double foo = foo( 0.0 ); $\C{// prints D}$
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| 57 | foo( foo ); $\C{// prints 3., where left-hand side of expression is void}$
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| 58 | }
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| 59 | \end{cfa}
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| 60 |
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| 61 |
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| 62 | \section{\lstinline{with} Statement}\label{s:with}
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| 63 | The \CFA @with@ statement is for exposing fields of an aggregate type within a scope, allowing field names without qualification.
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| 64 | This feature is also implemented in Pascal~\cite{Pascal}.
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| 65 | It can exist as a stand-alone statement or wrap a routine body to expose aggregate fields.
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| 66 | Examples of the @with@ statement are shown in \VRef[Listing]{l:cfa_with}.
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| 67 |
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| 68 | \begin{cfa}[caption={Example of \CFA \lstinline{with} statement},label={l:cfa_with}]
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| 69 | struct pair { double x, y; };
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| 70 | struct triple { int a, b, c; };
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| 71 | pair p;
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| 72 |
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| 73 | @with( p )@ { $\C{// stand-alone with}$
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| 74 | p.x = 6.28; p.y = 1.73; $\C{// long form}$
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| 75 | x = 6.28; y = 1.73; $\C{// short form}$
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| 76 | }
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| 77 | void foo( triple t, pair p ) @with( t, p )@ { $\C{// routine with}$
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| 78 | t.a = 1; t.b = 2; t.c = 3; p.x = 3.14; p.y = 2.71; $\C{// long form}$
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| 79 | a = 1; b = 2; c = 3; x = 3.14; y = 2.71; $\C{// short form}$
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| 80 | }
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| 81 | \end{cfa}
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| 82 |
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| 83 |
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| 84 | \section{Operators}\label{s:Operators}
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| 85 | Operators can be overloaded in \CFA with operator routines.
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| 86 | Operators in \CFA are named using an operator symbol and '@?@' to represent operands.
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| 87 | Examples of \CFA operators are shown in \VRef[Listing]{l:cfa_operate}.
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| 88 |
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| 89 | \begin{cfa}[caption={Example of \CFA operators},label={l:cfa_operate}]
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| 90 | struct coord {
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| 91 | double x, y, z;
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| 92 | };
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| 93 | coord ++@?@( coord & c ) with( c ) { $\C{// post increment}$
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| 94 | x++; y++; z++;
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| 95 | return c;
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| 96 | }
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| 97 | coord @?@<=@?@( coord op1, coord op2 ) with( op1 ) { $\C{// ambiguous with both parameters}$
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| 98 | return (x * x + y * y + z * z) <= (op2.x * op2.x + op2.y * op2.y + op2.z * op2.z);
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| 99 | }
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| 100 | \end{cfa}
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| 101 |
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| 102 |
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| 103 | \section{Constructors and Destructors}
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| 104 | Constructors and destructors in \CFA are special operator routines used for creation and destruction of objects.
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| 105 | The default constructor and destructor for a type are called implicitly upon creation and deletion, respectively.
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| 106 | Examples of \CFA constructors and destructors are shown in \VRef[Listing]{l:cfa_ctor}.
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| 107 |
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| 108 | \begin{cfa}[caption={Example of \CFA constructors and destructors},label={l:cfa_ctor}]
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| 109 | struct discrete_point {
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| 110 | int x, y;
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| 111 | };
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| 112 | void ?{}( discrete_point & this ) with(this) { $\C{// default constructor}$
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| 113 | [x, y] = 0;
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| 114 | }
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| 115 | void ?{}( discrete_point & this, int x, int y ) { $\C{// explicit constructor}$
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| 116 | this.[x, y] = [x, y];
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| 117 | }
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| 118 | void ^?{}( discrete_point & this ) with(this) { $\C{// destructor}$
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| 119 | ?{}( this ); $\C{// reset by calling default constructor}$
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| 120 | }
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| 121 | int main() {
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| 122 | discrete_point x, y{}; $\C{// implicit call to default ctor, ?\{\}}$
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| 123 | discrete_point s = { 2, -4 }, t{ 4, 2 }; $\C{// explicit call to specialized ctor}$
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| 124 | } // ^t{}, ^s{}, ^y{}, ^x{} implicit calls in reverse allocation order
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| 125 | \end{cfa}
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| 126 |
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| 127 |
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| 128 | \section{Polymorphism}\label{s:poly}
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| 129 | C supports limited polymorphism, often requiring users to implement polymorphism using a @void *@ (type erasure) approach.
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| 130 | \CFA extends C with generalized overloading polymorphism (see \VRef{s:Overloading}), as well as, parametric polymorphism and limited nominal inheritance.
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| 131 |
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| 132 | \subsection{Parametric Polymorphism}
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| 133 | \CFA provides parametric polymorphism in the form of @forall@, and @trait@s.
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| 134 | A @forall@ takes in a set of types and a list of constraints.
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| 135 | The declarations that follow the @forall@ are parameterized over the types listed that satisfy the constraints.
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| 136 | A list of @forall@ constraints can be refactored into a named @trait@ and reused in @forall@s.
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| 137 | Examples of \CFA parametric polymorphism are shown in \VRef[Listing]{l:cfa_poly}.
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| 138 |
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| 139 | \begin{cfa}[caption={Example of \CFA parametric polymorphism},label={l:cfa_poly}]
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| 140 | // sized() is a trait that means the type has a size
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| 141 | forall( V & | sized(V) ) $\C{// type params for trait}$
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| 142 | trait vector_space {
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| 143 | // dtor and copy ctor needed in constraints to pass by copy
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| 144 | void ?{}( V &, V & ); $\C{// copy ctor for return}$
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| 145 | void ^?{}( V & ); $\C{// dtor}$
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| 146 | V ?+?( V, V ); $\C{// vector addition}$
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| 147 | V ?*?( int, V ); $\C{// scalar multiplication}$
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| 148 | };
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| 149 |
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| 150 | forall( V & | vector_space( V ) ) {
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| 151 | V get_inverse( V v1 ) {
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| 152 | return -1 * v1; $\C{// can use ?*? routine defined in trait}$
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| 153 | }
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| 154 | V add_and_invert( V v1, V v2 ) {
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| 155 | return get_inverse( v1 + v2 ); $\C{// can use ?+? routine defined in trait}$
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| 156 | }
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| 157 | }
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| 158 | struct Vec1 { int x; };
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| 159 | void ?{}( Vec1 & this, Vec1 & other ) { this.x = other.x; }
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| 160 | void ?{}( Vec1 & this, int x ) { this.x = x; }
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| 161 | void ^?{}( Vec1 & this ) {}
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| 162 | Vec1 ?+?( Vec1 v1, Vec1 v2 ) { v1.x += v2.x; return v1; }
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| 163 | Vec1 ?*?( int c, Vec1 v1 ) { v1.x = v1.x * c; return v1; }
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| 164 |
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| 165 | struct Vec2 { int x; int y; };
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| 166 | void ?{}( Vec2 & this, Vec2 & other ) { this.x = other.x; this.y = other.y; }
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| 167 | void ?{}( Vec2 & this, int x ) { this.x = x; this.y = x; }
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| 168 | void ^?{}( Vec2 & this ) {}
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| 169 | Vec2 ?+?( Vec2 v1, Vec2 v2 ) { v1.x += v2.x; v1.y += v2.y; return v1; }
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| 170 | Vec2 ?*?( int c, Vec2 v1 ) { v1.x = v1.x * c; v1.y = v1.y * c; return v1; }
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| 171 |
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| 172 | int main() {
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| 173 | Vec1 v1{ 1 }; $\C{// create Vec1 and call ctor}$
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| 174 | Vec2 v2{ 2 }; $\C{// create Vec2 and call ctor}$
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| 175 | // can use forall defined routines since types satisfy trait
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| 176 | add_and_invert( get_inverse( v1 ), v1 );
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| 177 | add_and_invert( get_inverse( v2 ), v2 );
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| 178 | }
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| 179 | \end{cfa}
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| 180 |
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| 181 | \subsection{Inheritance}\label{s:Inheritance}
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| 182 | Inheritance in \CFA is taken from Plan-9 C's nominal inheritance.
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| 183 | In \CFA, @struct@s can @inline@ another struct type to gain its fields and masquerade as that type.
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| 184 | Examples of \CFA nominal inheritance are shown in \VRef[Listing]{l:cfa_inherit}.
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| 185 |
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| 186 | \begin{cfa}[caption={Example of \CFA nominal inheritance},label={l:cfa_inherit}]
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| 187 | struct one_d { double x; };
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| 188 | struct two_d {
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| 189 | @inline@ one_d;
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| 190 | double y;
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| 191 | };
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| 192 | struct three_d {
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| 193 | @inline@ two_d;
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| 194 | double z;
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| 195 | };
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| 196 | double get_x( one_d & d ){ return d.x; }
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| 197 |
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| 198 | struct dog {};
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| 199 | struct dog_food {
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| 200 | int count;
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| 201 | };
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| 202 | struct pet {
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| 203 | @inline@ dog;
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| 204 | @inline@ dog_food;
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| 205 | };
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| 206 | void pet_dog( dog & d ) { sout | "woof"; }
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| 207 | void print_food( dog_food & f ) { sout | f.count; }
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| 208 |
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| 209 | int main() {
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| 210 | one_d x;
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| 211 | two_d y;
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| 212 | three_d z;
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| 213 | x.x = 1;
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| 214 | y.x = 2;
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| 215 | z.x = 3;
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| 216 | get_x( x ); $\C{// returns 1;}$
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| 217 | get_x( y ); $\C{// returns 2;}$
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| 218 | get_x( z ); $\C{// returns 3;}$
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| 219 | pet p;
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| 220 | p.count = 5;
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| 221 | pet_dog( p ); $\C{// prints woof}$
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| 222 | print_food( p ); $\C{// prints 5}$
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| 223 | }
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| 224 | \end{cfa}
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| 225 |
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| 226 | % Local Variables: %
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| 227 | % tab-width: 4 %
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| 228 | % End: %
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