X-Git-Url: https://git.stderr.nl/gitweb?p=matthijs%2Fmaster-project%2Fdsd-paper.git;a=blobdiff_plain;f=c%CE%BBash.lhs;h=eb7d1fff8a11e82981bbb3b68a084b04ac06813a;hp=5668e326ec6b9038eed9796396c118f6883af8cf;hb=0025553cc63de81213b530f9277c617da74d1452;hpb=2e44f3b1a27636bcf3d878359d8cb317b2b57d45 diff --git "a/c\316\273ash.lhs" "b/c\316\273ash.lhs" index 5668e32..eb7d1ff 100644 --- "a/c\316\273ash.lhs" +++ "b/c\316\273ash.lhs" @@ -354,9 +354,10 @@ \newenvironment{xlist}[1][\rule{0em}{0em}]{% \begin{list}{}{% \settowidth{\labelwidth}{#1:} - \setlength{\labelsep}{\parindent} + \setlength{\labelsep}{0.5em} \setlength{\leftmargin}{\labelwidth} \addtolength{\leftmargin}{\labelsep} + \addtolength{\leftmargin}{\parindent} \setlength{\rightmargin}{0pt} \setlength{\listparindent}{\parindent} \setlength{\itemsep}{0 ex plus 0.2ex} @@ -585,15 +586,19 @@ by any (optimizing) \VHDL\ synthesis tool. consisting of: \hs{case} constructs, \hs{if-then-else} constructs, pattern matching, and guards. The easiest of these are the \hs{case} constructs (\hs{if} expressions can be very directly translated to - \hs{case} expressions). % Choice elements are translated to multiplexers + \hs{case} expressions). A \hs{case} construct is translated to a + multiplexer, where the control value is linked to the selection port and + the output of each case is linked to the corresponding input port on the + multiplexer. % A \hs{case} expression can in turn simply be translated to a conditional % assignment in \VHDL, where the conditions use equality comparisons % against the constructors in the \hs{case} expressions. - We can see two versions of a contrived example, the first + We can see two versions of a contrived example below, the first using a \hs{case} construct and the other using a \hs{if-then-else} constructs, in the code below. The example sums two values when they are equal or non-equal (depending on the predicate given) and returns 0 - otherwise. + otherwise. Both versions of the example roughly correspond to the same + netlist, which is depicted in \Cref{img:choice}. \begin{code} sumif pred a b = case pred of @@ -613,9 +618,6 @@ by any (optimizing) \VHDL\ synthesis tool. if a != b then a + b else 0 \end{code} - Both versions of the example correspond to the same netlist, which is - depicted in \Cref{img:choice}. - \begin{figure} \centerline{\includegraphics{choice-case}} \caption{Choice - sumif} @@ -626,22 +628,19 @@ by any (optimizing) \VHDL\ synthesis tool. matching. A function can be defined in multiple clauses, where each clause specifies a pattern. When the arguments match the pattern, the corresponding clause will be used. Expressions can also contain guards, - where the expression is only executed if the guard evaluates to true. A - pattern match (with optional guards) can be to a conditional assignments - in \VHDL, where the conditions are an equality test of the argument and - one of the patterns (combined with the guard if was present). A third - version of the earlier example, using both pattern matching and guards, - can be seen below: + where the expression is only executed if the guard evaluates to true. Like + \hs{if-then-else} constructs, pattern matching and guards have a + (straightforward) translation to \hs{case} constructs and can as such be + mapped to multiplexers. A third version of the earlier example, using both + pattern matching and guards, can be seen below. The version using pattern + matching and guards also has roughly the same netlist representation + (\Cref{img:choice}) as the earlier two versions of the example. \begin{code} sumif Eq a b | a == b = a + b sumif Neq a b | a != b = a + b sumif _ _ _ = 0 \end{code} - - The version using pattern matching and guards has the same netlist - representation (\Cref{img:choice}) as the earlier two versions of the - example. % \begin{figure} % \centerline{\includegraphics{choice-ifthenelse}} @@ -650,14 +649,17 @@ by any (optimizing) \VHDL\ synthesis tool. % \end{figure} \subsection{Types} - Haskell is a strongly-typed language, meaning that the type of a variable - or function is determined at compile-time. Not all of Haskell's typing - constructs have a clear translation to hardware, as such this section will - only deal with the types that do have a clear correspondence to hardware. - The translatable types are divided into two categories: \emph{built-in} - types and \emph{user-defined} types. Built-in types are those types for - which a direct translation is defined within the \CLaSH\ compiler; the - term user-defined types should not require any further elaboration. + Haskell is a statically-typed language, meaning that the type of a + variable or function is determined at compile-time. Not all of Haskell's + typing constructs have a clear translation to hardware, as such this + section will only deal with the types that do have a clear correspondence + to hardware. The translatable types are divided into two categories: + \emph{built-in} types and \emph{user-defined} types. Built-in types are + those types for which a direct translation is defined within the \CLaSH\ + compiler; the term user-defined types should not require any further + elaboration. The translatable types are also inferable by the compiler, + meaning that a developer does not have to annotate every function with a + type signature. % Translation of two most basic functional concepts has been % discussed: function application and choice. Before looking further @@ -675,6 +677,8 @@ by any (optimizing) \VHDL\ synthesis tool. % using translation rules that are discussed later on. \subsubsection{Built-in types} + The following types have direct translation defined within the \CLaSH\ + compiler: \begin{xlist} \item[\bf{Bit}] This is the most basic type available. It can have two values: @@ -709,7 +713,9 @@ by any (optimizing) \VHDL\ synthesis tool. This is a vector type that can contain elements of any other type and has a fixed length. The \hs{Vector} type constructor takes two type arguments: the length of the vector and the type of the elements - contained in it. + contained in it. The short-hand notation used for the vector type in + the rest of paper is: \hs{[a|n]}. Where the \hs{a} is the element + type, and \hs{n} is the length of the vector. % The state type of an 8 element register bank would then for example % be: @@ -723,12 +729,12 @@ by any (optimizing) \VHDL\ synthesis tool. % (The 32 bit word type as defined above). In other words, the % \hs{RegisterState} type is a vector of 8 32-bit words. A fixed size % vector is translated to a \VHDL\ array type. - \item[\bf{RangedWord}] + \item[\bf{Index}] This is another type to describe integers, but unlike the previous two it has no specific bit-width, but an upper bound. This means that its range is not limited to powers of two, but can be any number. - A \hs{RangedWord} only has an upper bound, its lower bound is - implicitly zero. The main purpose of the \hs{RangedWord} type is to be + An \hs{Index} only has an upper bound, its lower bound is + implicitly zero. The main purpose of the \hs{Index} type is to be used as an index to a \hs{Vector}. % \comment{TODO: Perhaps remove this example?} To define an index for @@ -749,36 +755,32 @@ by any (optimizing) \VHDL\ synthesis tool. \subsubsection{User-defined types} There are three ways to define new types in Haskell: algebraic data-types with the \hs{data} keyword, type synonyms with the \hs{type} - keyword and datatype renamings with the \hs{newtype} keyword. \GHC\ - offers a few more advanced ways to introduce types (type families, - existential typing, {\small{GADT}}s, etc.) which are not standard - Haskell. These are not currently supported. + keyword and datatype renaming constructs with the \hs{newtype} keyword. + \GHC\ offers a few more advanced ways to introduce types (type families, + existential typing, {\small{GADT}}s, etc.) which are not standard Haskell. + As it is currently unclear how these advanced type constructs correspond + with hardware, they are for now unsupported by the \CLaSH\ compiler Only an algebraic datatype declaration actually introduces a - completely new type, for which we provide the \VHDL\ translation - below. Type synonyms and renamings only define new names for - existing types, where synonyms are completely interchangeable and - renamings need explicit conversiona. Therefore, these do not need - any particular \VHDL\ translation, a synonym or renamed type will - just use the same representation as the original type. The - distinction between a renaming and a synonym does no longer matter - in hardware and can be disregarded in the generated \VHDL. For algebraic - types, we can make the following distinction: + completely new type. Type synonyms and renaming constructs only define new + names for existing types, where synonyms are completely interchangeable + and renaming constructs need explicit conversions. Therefore, these do not + need any particular translation, a synonym or renamed type will just use + the same representation as the original type. The distinction between a + renaming and a synonym does no longer matter in hardware and can be + disregarded in the translation process. For algebraic types, we can make + the following distinction: \begin{xlist} \item[\bf{Single constructor}] Algebraic datatypes with a single constructor with one or more fields, are essentially a way to pack a few values together in a - record-like structure. An example of such a type is the following pair - of integers: - + record-like structure. Haskell's built-in tuple types are also defined + as single constructor algebraic types An example of a single + constructor type is the following pair of integers: \begin{code} data IntPair = IntPair Int Int \end{code} - - Haskell's builtin tuple types are also defined as single - constructor algebraic types and are translated according to this - rule by the \CLaSH\ compiler. % These types are translated to \VHDL\ record types, with one field % for every field in the constructor. \item[\bf{No fields}] @@ -786,7 +788,11 @@ by any (optimizing) \VHDL\ synthesis tool. fields are essentially a way to get an enumeration-like type containing alternatives. Note that Haskell's \hs{Bool} type is also defined as an enumeration type, but we have a fixed translation for - that. + that. An example of such an enum type is the type that represents the + colors in a traffic light: + \begin{code} + data TrafficLight = Red | Orange | Green + \end{code} % These types are translated to \VHDL\ enumerations, with one % value for each constructor. This allows references to these % constructors to be translated to the corresponding enumeration @@ -810,7 +816,7 @@ by any (optimizing) \VHDL\ synthesis tool. \comment{TODO: Use vectors instead of lists?} \begin{code} - append :: [a] -> a -> [a] + append :: [a|n] -> a -> [a|n + 1] \end{code} This type is parameterized by \hs{a}, which can contain any type at