many updates

[phd-thesis.git] / appendix / clean_for_haskell_programmers.tex

diff --git a/appendix/clean_for_haskell_programmers.tex b/appendix/clean_for_haskell_programmers.tex
index 715964c..65dfb87 100644 (file)
--- a/appendix/clean_for_haskell_programmers.tex
+++ b/appendix/clean_for_haskell_programmers.tex
@@ -1,5 +1,25 @@
+\documentclass[../thesis.tex]{subfiles}
+
+\begin{document}
+
+\ifSubfilesClassLoaded{
+       \pagenumbering{arabic}
+}{
+}
+
+\chapter{\texorpdfstring{\glsentrytext{CLEAN}}{Clean} for \texorpdfstring{\glsentrytext{HASKELL}}{Haskell} Programmers}%
+\label{chp:clean_for_haskell_programmers}
+
+This note is meant to give people who are familiar with the functional programming language \gls{HASKELL} a consise overview of \gls{CLEAN} language elements and how they differ from \gls{HASKELL}.
+The goal is to support the reader when reading \gls{CLEAN} code.
+Table~\ref{tbl:syn_clean_haskell} shows frequently occuring \gls{CLEAN} language elements on the left side and their \gls{HASKELL} equivalent on the right side.
+Obviously, this summary is not exhaustive.
+Some \gls{CLEAN} language elements that are not easily translatable to \gls{HASKELL} and thus do not occur in the summary following below.
+We hope you enjoy these notes and that it aids you in reading \gls{CLEAN} programs.
+

 While \gls{CLEAN} and \gls{HASKELL} were both conceived around 1987 and have similar syntax, there are some subtle differences in syntax and functionality.
 While \gls{CLEAN} and \gls{HASKELL} were both conceived around 1987 and have similar syntax, there are some subtle differences in syntax and functionality.

-This section describes some of the history of \gls{CLEAN} and provides a crash course in \gls{CLEAN} pecularities writen for \gls{HASKELL} programmers.
+This section describes some of the history of \gls{CLEAN} and provides a crash course in \gls{CLEAN} pecularities written for \gls{HASKELL} programmers.
+It is based on the 

 
 \Gls{CLEAN}---acronym for Clean \acrlong{LEAN}~\cite{barendregt_towards_1987}---, was originally designed as a \gls{GRS} core language but quickly served as an intermediate language for other functional languages~\cite{brus_clean_1987}.
 In the early days it has also been called \emph{Concurrent} \gls{CLEAN}~\cite{nocker_concurrent_1991} but these days the language has no support for this anymore.
 
 \Gls{CLEAN}---acronym for Clean \acrlong{LEAN}~\cite{barendregt_towards_1987}---, was originally designed as a \gls{GRS} core language but quickly served as an intermediate language for other functional languages~\cite{brus_clean_1987}.
 In the early days it has also been called \emph{Concurrent} \gls{CLEAN}~\cite{nocker_concurrent_1991} but these days the language has no support for this anymore.


@@ -10,7 +30,7 @@ However, over the years, the syntax got friendlier and it currently it looks a l
 In the past, a \emph{double-edged} fronted even existed that allowed \gls{CLEAN} to be extended with \gls{HASKELL98} syntax and vice versa, however this frontend is no longer maintained~\cite{groningen_exchanging_2010}.
 This chapter therefore gives a brief syntactical and functional comparison, a complete specification of the \gls{CLEAN} language can be found in the latest language report~\cite{plasmeijer_clean_2021}.
 Many of this is based on work by Achten although that was based on \gls{CLEAN} 2.1 and \gls{HASKELL98}~\cite{achten_clean_2007}.
 In the past, a \emph{double-edged} fronted even existed that allowed \gls{CLEAN} to be extended with \gls{HASKELL98} syntax and vice versa, however this frontend is no longer maintained~\cite{groningen_exchanging_2010}.
 This chapter therefore gives a brief syntactical and functional comparison, a complete specification of the \gls{CLEAN} language can be found in the latest language report~\cite{plasmeijer_clean_2021}.
 Many of this is based on work by Achten although that was based on \gls{CLEAN} 2.1 and \gls{HASKELL98}~\cite{achten_clean_2007}.

-When \gls{HASKELL} is mentioned I actually mean \gls{GHC}'s \gls{HASKELL} and by \gls{CLEAN} I mean \gls{CLEAN} 3.1's \gls{ITASK} compiler.
+When \gls{HASKELL} is mentioned we actually mean \gls{GHC}'s \gls{HASKELL}\footnote{If an extension is enabled, a footnote is added stating that \GHCmod{SomeExtension} is required.} this is denoted and by \gls{CLEAN} we mean \gls{CLEAN} 3.1's compiler with the \gls{ITASK} extensions.

 
 \section{Features}
 \subsection{Modules}
 
 \section{Features}
 \subsection{Modules}


@@ -23,17 +43,17 @@ Choosing what is exported in \gls{HASKELL} is done using the \haskellinline{modu
 
 \subsection{Strictness}
 In \gls{CLEAN}, by default, all expressions are evaluated lazily.
 
 \subsection{Strictness}
 In \gls{CLEAN}, by default, all expressions are evaluated lazily.

-Types can be annotated with a strictness attribute (\cleaninline{!}), resulting in the values being evaluated to head-normal form before the function is entered.
+Types can be annotated with a strictness attributes (\cleaninline{!}), resulting in the values being evaluated to head-normal form before the function is entered.

 In \gls{HASKELL}, in patterns, strictness can be enforced using \haskellinline{!}\requiresGHCmod{BangPatterns}.
 Within functions the strict let (\cleaninline{#!}) can be used to force evaluate an expression, in \gls{HASKELL} \haskellinline{seq} or \haskellinline{\$!} is used for this.
 
 \subsection{Uniqueness typing}
 In \gls{HASKELL}, in patterns, strictness can be enforced using \haskellinline{!}\requiresGHCmod{BangPatterns}.
 Within functions the strict let (\cleaninline{#!}) can be used to force evaluate an expression, in \gls{HASKELL} \haskellinline{seq} or \haskellinline{\$!} is used for this.
 
 \subsection{Uniqueness typing}

-Types in \gls{CLEAN} may be \emph{unique}, which means that they may not be shared\todo{cite}.
+Types in \gls{CLEAN} may be \emph{unique}, which means that they may not be shared~\cite{barendsen_uniqueness_1996}.

 The uniqueness type system allows the compiler to generate efficient code because unique data structures can be destructively updated.
 The uniqueness type system allows the compiler to generate efficient code because unique data structures can be destructively updated.

-Furthermore, uniqueness typing serves as a model for side effects as well.
-\Gls{CLEAN} uses the \emph{world-as-value} paradigm where \cleaninline{World} represents the external environment and is always unique.
+Furthermore, uniqueness typing serves as a model for side effects as well~\cite{achten_high_1993,achten_ins_1995}.
+\Gls{CLEAN} uses the \emph{world-as-value} paradigm where \cleaninline{World} represents the external environment and is always unique~\cite{backus_introduction_1990}.

 A program with side effects is characterised by a \cleaninline{Start :: *World -> *World} start function.
 A program with side effects is characterised by a \cleaninline{Start :: *World -> *World} start function.

-In \gls{HASKELL}, interaction with the world is done using the \haskellinline{IO} monad.
+In \gls{HASKELL}, interaction with the world is done using the \haskellinline{IO} monad~\cite{peyton_jones_imperative_1993}.

 The \haskellinline{IO} monad could very well be---and actually is---implemented in \gls{CLEAN} using a state monad with the \cleaninline{World} as a state.
 Besides marking types as unique, it is also possible to mark them with uniqueness attributes variables \cleaninline{u:} and define constraints on them.
 For example, to make sure that an argument of a function is at least as unique as another argument.
 The \haskellinline{IO} monad could very well be---and actually is---implemented in \gls{CLEAN} using a state monad with the \cleaninline{World} as a state.
 Besides marking types as unique, it is also possible to mark them with uniqueness attributes variables \cleaninline{u:} and define constraints on them.
 For example, to make sure that an argument of a function is at least as unique as another argument.


@@ -41,7 +61,7 @@ Finally, using \cleaninline{.} (a dot), it is possible to state that several var
 Uniqueness is propagated automatically in function types but must be marked manually in data types.
 Examples can be seen in \cref{lst:unique_examples}.
 
 Uniqueness is propagated automatically in function types but must be marked manually in data types.
 Examples can be seen in \cref{lst:unique_examples}.
 

-\begin{lstClean}[label={lst:unique_examples},caption={Examples of uniqueness annotations}]
+\begin{lstClean}[label={lst:unique_examples},caption={Examples of uniqueness annotations.}]

 f :: *a -> *a                // f works on unique values only
 f :: .a -> .a                // f works on unique and non-unique values
 f :: v:a u:b -> u:b, [v<=u]  // f works when a is less unique than b
 f :: *a -> *a                // f works on unique values only
 f :: .a -> .a                // f works on unique and non-unique values
 f :: v:a u:b -> u:b, [v<=u]  // f works when a is less unique than b


@@ -51,22 +71,46 @@ f :: v:a u:b -> u:b, [v<=u]  // f works when a is less unique than b
 %:: T = T (Int -> *(*World -> *World)) // Writing :: T = T (Int *World -> *World) won't work
 
 \subsection{Expressions}
 %:: T = T (Int -> *(*World -> *World)) // Writing :: T = T (Int *World -> *World) won't work
 
 \subsection{Expressions}

-\todo[inline]{Matches pattern expression \texttt{=:}}
+Patterns in \gls{CLEAN} can be used as predicates as well~\cite[Chp.~3.4.3]{plasmeijer_clean_2021}.
+Using the \cleaninline{=:} operator, a value can be tested against a pattern.
+Variable names are not allowed but wildcard patterns \cleaninline{\_} are.
+
+\begin{lstClean}[label={lst:matches_pattern_expression},caption={Examples of \emph{matches pattern} expressions.}]
+isNil :: [a] -> Bool
+isNil l = l=:[]

 
 

-\todo[inline]{Let before}
+:: T = A Int | B Bool
+
+ifAB :: T a a -> a
+ifAB x ifa ifb = if (x =: (A _)) ifa ifb
+\end{lstClean}
+
+Due to the nature of uniqueness typing, many functions in \gls{CLEAN} are state transition functions with possibly unique states.
+The \emph{let before} construct allows the programmer to specify sequential actions without having to invent unique names for the different versions of the state.
+\Cref{lst:let_before} shows an example of the usage of the \emph{let before} construct (adapted from~\cite[Chp.~3.5.4]{plasmeijer_clean_2021}).
+
+\begin{lstClean}[label={lst:let_before},caption={Let before expression example.}]
+readChars :: *File -> ([Char], *File)
+readChars file
+# (ok, char, file) = freadc file
+| not ok           = ([], file)
+# (chars, file)    = readChars file
+= ([char:chars], file)
+\end{lstClean}

 
 \subsection{Generics}
 Polytypic functions~\cite{jeuring_polytypic_1996}---also known as generic or kind-indexed fuctions---are built into \gls{CLEAN}~\cite[Chp.~7.1]{plasmeijer_clean_2021}\cite{alimarine_generic_2005} whereas in \gls{HASKELL} they are implemented as a library~\cite[Chp.~6.19.1]{ghc_team_ghc_2021}.
 
 \subsection{Generics}
 Polytypic functions~\cite{jeuring_polytypic_1996}---also known as generic or kind-indexed fuctions---are built into \gls{CLEAN}~\cite[Chp.~7.1]{plasmeijer_clean_2021}\cite{alimarine_generic_2005} whereas in \gls{HASKELL} they are implemented as a library~\cite[Chp.~6.19.1]{ghc_team_ghc_2021}.

+The implementation of generics in \gls{CLEAN} is very similar to that of Generic H$\forall$skell~\cite{hinze_generic_2003}.

 %When calling a generic function, the kind must always be specified and depending on the kind, the function may require more arguments.
 
 For example, defining a generic equality is done as in \cref{lst:generic_eq}.
 \lstinputlisting[language=Clean,firstline=4,label={lst:generic_eq},caption={Generic equality function in \gls{CLEAN}.}.]{lst/generic_eq.icl}
 
 %When calling a generic function, the kind must always be specified and depending on the kind, the function may require more arguments.
 
 For example, defining a generic equality is done as in \cref{lst:generic_eq}.
 \lstinputlisting[language=Clean,firstline=4,label={lst:generic_eq},caption={Generic equality function in \gls{CLEAN}.}.]{lst/generic_eq.icl}
 

-Metadata about the types is available using the \cleaninline{of} syntax that gives the function access to metadata records, as can be seen in \cref{lst:generic_print} showing a generic print function. This abundance of metadata allows for very complex generic functions that near the expression level of template metaprogramming\todo[inline]{crossref chapter c-code generation}.
+Metadata about the types is available using the \cleaninline{of} syntax that gives the function access to metadata records, as can be seen in \cref{lst:generic_print} showing a generic print function. This abundance of metadata allows for very complex generic functions that near the expression level of template metaprogramming\ifSubfilesClassLoaded{}{ (See \cref{chp:first-class_datatypes})}.

 \lstinputlisting[language=Clean,firstline=4,label={lst:generic_print},caption={Generic print function in \gls{CLEAN}.}]{lst/generic_print.icl}
 
 \lstinputlisting[language=Clean,firstline=4,label={lst:generic_print},caption={Generic print function in \gls{CLEAN}.}]{lst/generic_print.icl}
 

-\subsection{\glsentrytext{GADT}s}
-GADTs are enriched data types that allow the type instantiation of the constructor to be explicitly defined~\cite{cheney_first-class_2003,hinze_fun_2003}.
+\subsection{\texorpdfstring{\glsentrytext{GADT}}{GADT}s}
+\Glspl{GADT} are enriched data types that allow the type instantiation of the constructor to be explicitly defined~\cite{cheney_first-class_2003,hinze_fun_2003}.

 While \glspl{GADT} are not natively supported in \gls{CLEAN}, they can be simulated using embedding-projection pairs or equivalence types~\cite[Sec.~2.2]{cheney_lightweight_2002}.
 To illustrate this, \cref{lst:gadt_clean} shows an example \gls{GADT} that would be implemented in \gls{HASKELL} as done in \cref{lst:gadt_haskell}\requiresGHCmod{GADTs}.
 
 While \glspl{GADT} are not natively supported in \gls{CLEAN}, they can be simulated using embedding-projection pairs or equivalence types~\cite[Sec.~2.2]{cheney_lightweight_2002}.
 To illustrate this, \cref{lst:gadt_clean} shows an example \gls{GADT} that would be implemented in \gls{HASKELL} as done in \cref{lst:gadt_haskell}\requiresGHCmod{GADTs}.
 


@@ -107,9 +151,9 @@ To illustrate this, \cref{lst:gadt_clean} shows an example \gls{GADT} that would
        \cleaninline{True :: Bool} & \haskellinline{True :: Bool}\\
        \cleaninline{toInteger 42 :: Integer} & \haskellinline{42 :: Integer}\\
        \cleaninline{38.0 :: Real} & \haskellinline{38.0 :: Float -- or Double}\\
        \cleaninline{True :: Bool} & \haskellinline{True :: Bool}\\
        \cleaninline{toInteger 42 :: Integer} & \haskellinline{42 :: Integer}\\
        \cleaninline{38.0 :: Real} & \haskellinline{38.0 :: Float -- or Double}\\

-       \cleaninline{"Hello" +++ "World" :: String}\footnote{Strings are represented as unboxed character arrays.}
-               & \haskellinline{"Hello" ++ "World" :: String}\footnote{Strings are represented as lists of characters by default but may be overloaded as well if \GHCmod{OverloadedStrings} is enabled.}\\
-       \cleaninline{['Hello'] :: [Char]} & \haskellinline{"Hello" :: String}\\
+       \cleaninline{\"Hello\" +++ \"World\" :: String}\footnote{Strings are represented as unboxed character arrays.}
+               & \haskellinline{\"Hello\" ++ \"World\" :: String}\footnote{Strings are represented as lists of characters by default but may be overloaded as well if \GHCmod{OverloadedStrings} is enabled.}\\
+       \cleaninline{['Hello'] :: [Char]} & \haskellinline{\"Hello\" :: String}\\

        \cleaninline{?t} & \haskellinline{Maybe t}\\
        \cleaninline{(?None, ?Just e)} & \haskellinline{(Nothing, Just e)}\\
 
        \cleaninline{?t} & \haskellinline{Maybe t}\\
        \cleaninline{(?None, ?Just e)} & \haskellinline{(Nothing, Just e)}\\
 


@@ -122,7 +166,7 @@ To illustrate this, \cref{lst:gadt_clean} shows an example \gls{GADT} that would
        \cleaninline{:: T a0 ...} & \haskellinline{data T a0 ...}\\
        \quad\cleaninline{= \{ f0 :: t0, ..., fn :: tn \} } & \quad\haskellinline{= T \{ f0 :: t0, ..., fn :: tn \} }\\
        \cleaninline{:: T a0 ... =: t} & \haskellinline{newtype T a0 ... = t}\\
        \cleaninline{:: T a0 ...} & \haskellinline{data T a0 ...}\\
        \quad\cleaninline{= \{ f0 :: t0, ..., fn :: tn \} } & \quad\haskellinline{= T \{ f0 :: t0, ..., fn :: tn \} }\\
        \cleaninline{:: T a0 ... =: t} & \haskellinline{newtype T a0 ... = t}\\

-       \cleaninline{:: T = E.t Box t \& C t} & \haskellinline{data T = forall t.C t => Box t}\requiresGHCmod{ExistentialQuantification}\\
+       \cleaninline{:: T = E.t: Box t \& C t} & \haskellinline{data T = forall t.C t => Box t}\requiresGHCmod{ExistentialQuantification}\\

 
        \midrule
        \multicolumn{2}{c}{Function types}\\
 
        \midrule
        \multicolumn{2}{c}{Function types}\\


@@ -220,3 +264,5 @@ To illustrate this, \cref{lst:gadt_clean} shows an example \gls{GADT} that would
        \bottomrule
 \end{longtable}
 
        \bottomrule
 \end{longtable}
 

+\input{subfilepostamble}
+\end{document}