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Quick start
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<H1 CLASS="chapter"><A NAME="htoc6">Chapter 2</A> Quick start</H1>
First install <FONT COLOR=purple>Frown</FONT> as described in Sec. <A HREF="Manual002.html#sec:install">1.1</A>. Then enter
the directory <TT>QuickStart</TT>.
<TABLE border=0 cellspacing=0 cellpadding=0>
<TR><TD ALIGN=left NOWRAP><TT> ralf/Frown> cd QuickStart
</TT></TD>
</TR></TABLE>
The file <TT>Tiger.lg</TT>, listed in Fig. <A HREF="#fig:tiger">2.1</A>, contains a
medium-sized grammar for an imperative language.
<BLOCKQUOTE CLASS="figure"><DIV CLASS="center"><HR WIDTH="80%" SIZE=2></DIV>
<FONT SIZE=2>A grammar file consists of two parts: the specification of the
grammar, enclosed in special curly braces, and Haskell source code.
The source file typically starts with a Haskell module header.
<TABLE BORDER="2" BGCOLOR="#E0E0E0" WIDTH="100%"><TR><TD>
</FONT><TABLE border=0 cellspacing=0 cellpadding=0>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> <B>module</B> <I>Tiger</I></TT></FONT><FONT SIZE=2><TT> <B>where</B></TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> <B>import</B> <I>Lexer</I></TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> <B>import</B> <I>Syntax</I></TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> <B>import</B> <I>Prelude</I></TT></FONT><FONT SIZE=2><TT> hiding (exp)</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> </TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> %{</TT></FONT></TD>
</TR></TABLE><FONT SIZE=2>
</TD></TR></TABLE><P>
The grammar part begins here. A context-free grammar consists of sets
of terminal and nonterminal symbols, a set of start symbols, and set
of productions or grammar rules. The declaration below introduces the
terminal symbols. Each terminal is given by a Haskell pattern of type
<TT><I>Terminal</I></TT></FONT><FONT SIZE=2>.
<TABLE BORDER="2" BGCOLOR="#E0E0E0" WIDTH="100%"><TR><TD>
</FONT><TABLE border=0 cellspacing=0 cellpadding=0>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> <I>Terminal</I></TT></FONT><FONT SIZE=2><TT> = <I>DO</I></TT></FONT><FONT SIZE=2><TT> | <I>ELSE</I></TT></FONT><FONT SIZE=2><TT> | <I>END</I></TT></FONT><FONT SIZE=2><TT> | <I>FUNCTION</I></TT></FONT><FONT SIZE=2><TT> | <I>IF</I></TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> | <I>IN</I></TT></FONT><FONT SIZE=2><TT> | <I>LET</I></TT></FONT><FONT SIZE=2><TT> | <I>THEN</I></TT></FONT><FONT SIZE=2><TT> | <I>VAR</I></TT></FONT><FONT SIZE=2><TT> | <I>WHILE</I></TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> | <I>ASSIGN</I></TT></FONT><FONT SIZE=2><TT> as ":=" | <I>COLON</I></TT></FONT><FONT SIZE=2><TT> as ":" | <I>COMMA</I></TT></FONT><FONT SIZE=2><TT> as "," | <I>CPAREN</I></TT></FONT><FONT SIZE=2><TT> as ")"</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> | <I>DIV</I></TT></FONT><FONT SIZE=2><TT> as "/" | <I>EQU</I></TT></FONT><FONT SIZE=2><TT> as "=" | <I>LST</I></TT></FONT><FONT SIZE=2><TT> as "<=" | <I>MINUS</I></TT></FONT><FONT SIZE=2><TT> as "-"</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> | <I>NEG</I></TT></FONT><FONT SIZE=2><TT> as "~" | <I>OPAREN</I></TT></FONT><FONT SIZE=2><TT> as "(" | <I>PLUS</I></TT></FONT><FONT SIZE=2><TT> as "+" | <I>SEMI</I></TT></FONT><FONT SIZE=2><TT> as ";"</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> | <I>TIMES</I></TT></FONT><FONT SIZE=2><TT> as "*"</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> | <I>ID</I></TT></FONT><FONT SIZE=2><TT> {<I>String</I></TT></FONT><FONT SIZE=2><TT>} | <I>INT</I></TT></FONT><FONT SIZE=2><TT> {<I>String</I></TT></FONT><FONT SIZE=2><TT>};
</TT></FONT></TD>
</TR></TABLE><FONT SIZE=2>
</TD></TR></TABLE><P>
A terminal symbol may carry a semantic value or attribute. The Haskell
type of the semantic value is given in curly braces. As a rule,
Haskell source code is always enclosed in curly braces within the
grammar part. The as-clauses define shortcuts for terminals, which may
then be used in the productions.<BR>
<BR>
The declaration below introduces a nonterminal symbol called <TT>exp</TT>
followed by sixteen productions for that symbol. The asterix marks
<TT>exp</TT> as a start symbol; <TT>exp</TT> has a single attribute of type <TT><I>Expr</I></TT></FONT><FONT SIZE=2>.
<TABLE BORDER="2" BGCOLOR="#E0E0E0" WIDTH="100%"><TR><TD>
</FONT><TABLE border=0 cellspacing=0 cellpadding=0>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> *exp {<I>Expr</I></TT></FONT><FONT SIZE=2><TT>};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> exp {<I>Var</I></TT></FONT><FONT SIZE=2><TT> v} : <I>ID</I></TT></FONT><FONT SIZE=2><TT> {v};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Block</I></TT></FONT><FONT SIZE=2><TT> es} | "(", sepBy exp ";" {es}, ")";</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Int</I></TT></FONT><FONT SIZE=2><TT> i } | <I>INT</I></TT></FONT><FONT SIZE=2><TT> {i};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Un</I></TT></FONT><FONT SIZE=2><TT> <I>Neg</I></TT></FONT><FONT SIZE=2><TT> e} | "-", exp {e}, prec "~";</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Call</I></TT></FONT><FONT SIZE=2><TT> f es} | <I>ID</I></TT></FONT><FONT SIZE=2><TT> {f}, "(", sepBy exp "," {es}, ")";</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Bin</I></TT></FONT><FONT SIZE=2><TT> e1 <I>Eq</I></TT></FONT><FONT SIZE=2><TT> e2} | exp {e1}, "=", exp {e2};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Bin</I></TT></FONT><FONT SIZE=2><TT> e1 <I>Leq</I></TT></FONT><FONT SIZE=2><TT> e2} | exp {e1}, "<=", exp {e2};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Bin</I></TT></FONT><FONT SIZE=2><TT> e1 <I>Add</I></TT></FONT><FONT SIZE=2><TT> e2} | exp {e1}, "+", exp {e2};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Bin</I></TT></FONT><FONT SIZE=2><TT> e1 <I>Sub</I></TT></FONT><FONT SIZE=2><TT> e2} | exp {e1}, "-", exp {e2};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Bin</I></TT></FONT><FONT SIZE=2><TT> e1 <I>Mul</I></TT></FONT><FONT SIZE=2><TT> e2} | exp {e1}, "*", exp {e2};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Bin</I></TT></FONT><FONT SIZE=2><TT> e1 <I>Div</I></TT></FONT><FONT SIZE=2><TT> e2} | exp {e1}, "/", exp {e2};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Assign</I></TT></FONT><FONT SIZE=2><TT> v e} | <I>ID</I></TT></FONT><FONT SIZE=2><TT> {v}, ":=", exp {e};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>IfThen</I></TT></FONT><FONT SIZE=2><TT> e e1} | <I>IF</I></TT></FONT><FONT SIZE=2><TT>, exp {e}, <I>THEN</I></TT></FONT><FONT SIZE=2><TT>, exp {e1};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>IfElse</I></TT></FONT><FONT SIZE=2><TT> e e1 e2} | <I>IF</I></TT></FONT><FONT SIZE=2><TT>, exp {e}, <I>THEN</I></TT></FONT><FONT SIZE=2><TT>, exp {e1}, <I>ELSE</I></TT></FONT><FONT SIZE=2><TT>, exp {e2};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>While</I></TT></FONT><FONT SIZE=2><TT> e e1} | <I>WHILE</I></TT></FONT><FONT SIZE=2><TT>, exp {e}, <I>DO</I></TT></FONT><FONT SIZE=2><TT>, exp {e1};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {<I>Let</I></TT></FONT><FONT SIZE=2><TT> ds es} | <I>LET</I></TT></FONT><FONT SIZE=2><TT>, many dec {ds}, <I>IN</I></TT></FONT><FONT SIZE=2><TT>, sepBy exp ";" {es}, <I>END</I></TT></FONT><FONT SIZE=2><TT>;
</TT></FONT></TD>
</TR></TABLE><FONT SIZE=2>
</TD></TR></TABLE><P>
Left-hand and right-hand side of a production are separated by a
colon; symbols on the right are separated by commas and terminated by
a semicolon. Alternative right-hand sides are separated by a vertical
bar. <BR>
<BR>
The pieces in curly braces constitute Haskell source code. Each rule
can be seen as a function from the right-hand to the left-hand
side. On the right-hand side, Haskell variables are used to name the
values of attributes. The values of the attributes on the left-hand
side are given by Haskell expressions, in which the variables of the
right-hand side occur free.<BR>
<BR>
The last production makes use of two (predefined) rule schemes: <TT>many x</TT>
implements the repetition of the symbol <TT>x</TT>, and <TT>sepBy x sep</TT>
denotes a repetition of <TT>x</TT> symbols separated by <TT>sep</TT> symbols.<BR>
<BR>
The above productions are ambiguous as, for instance, <TT>1 + 2 * 3</TT> has
two derivations. The ambiguity can be resolved by assigning
precedences to terminal symbols.
<TABLE BORDER="2" BGCOLOR="#E0E0E0" WIDTH="100%"><TR><TD>
</FONT><TABLE border=0 cellspacing=0 cellpadding=0>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> left 7 "~"; left 6 "*"; left 6 "/"; left 5 "+"; left 5 "-";</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> right 0 <I>THEN</I></TT></FONT><FONT SIZE=2><TT>; right 0 <I>ELSE</I></TT></FONT><FONT SIZE=2><TT>; </TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> nonassoc 4 "<="; nonassoc 4 "="; nonassoc 0 <I>DO</I></TT></FONT><FONT SIZE=2><TT>; nonassoc 0 ":=";
</TT></FONT></TD>
</TR></TABLE><FONT SIZE=2>
</TD></TR></TABLE><P>
The following declarations define the nonterminal <TT>dec</TT> and three
further nonterminals.
<TABLE BORDER="2" BGCOLOR="#E0E0E0" WIDTH="100%"><TR><TD>
</FONT><TABLE border=0 cellspacing=0 cellpadding=0>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> dec {<I>Decl</I></TT></FONT><FONT SIZE=2><TT>};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> dec {d} : vardec {d};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> {d} | fundec {d};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> </TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> vardec {<I>Decl</I></TT></FONT><FONT SIZE=2><TT>};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> vardec {<I>Variable</I></TT></FONT><FONT SIZE=2><TT> v e} : <I>VAR</I></TT></FONT><FONT SIZE=2><TT>, <I>ID</I></TT></FONT><FONT SIZE=2><TT> {v}, ":=", exp {e};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> </TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> fundec {<I>Decl</I></TT></FONT><FONT SIZE=2><TT>};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> fundec {<I>Function</I></TT></FONT><FONT SIZE=2><TT> f xs e} : <I>FUNCTION</I></TT></FONT><FONT SIZE=2><TT>, <I>ID</I></TT></FONT><FONT SIZE=2><TT> {f}, "(", sepBy (<I>ID</I></TT></FONT><FONT SIZE=2><TT> {}) "," {xs}, ")", "=", exp {e};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> </TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> formal {(<I>Ident</I></TT></FONT><FONT SIZE=2><TT>, <I>TyIdent</I></TT></FONT><FONT SIZE=2><TT>)};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> formal {(v, t)} : <I>ID</I></TT></FONT><FONT SIZE=2><TT> {v}, ":", <I>ID</I></TT></FONT><FONT SIZE=2><TT> {t};</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> </TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> }%
</TT></FONT></TD>
</TR></TABLE><FONT SIZE=2>
</TD></TR></TABLE><P>
The grammar part ends here. The source file typically includes a
couple of Haskell declarations. The user-defined function <TT>frown</TT> is
the error routine invoked by the parser in case of a syntax error; its
definition is mandatory.
<TABLE BORDER="2" BGCOLOR="#E0E0E0" WIDTH="100%"><TR><TD>
</FONT><TABLE border=0 cellspacing=0 cellpadding=0>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> frown _ = error "syntax error"</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> </TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> tc f = <B>do</B> { putStrLn "*** reading ..."; s <- readFile f; print s;</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> putStrLn "*** lexing ..."; <B>let</B> {ts = lexer s}; print ts;</TT></FONT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><FONT SIZE=2><TT>> putStrLn "*** parsing ..."; e <- exp ts; print e }</TT></FONT></TD>
</TR></TABLE><FONT SIZE=2>
</TD></TR></TABLE><P>
<BR>
<BR>
</FONT><DIV CLASS="center"><FONT SIZE=2>Figure 2.1: </FONT><A NAME="fig:tiger"></A><FONT SIZE=2>A sample <FONT COLOR=purple>Frown</FONT></FONT><FONT SIZE=2> grammar file.</FONT></DIV><BR>
<BR>
<FONT SIZE=2>
</FONT><DIV CLASS="center"><HR WIDTH="80%" SIZE=2></DIV></BLOCKQUOTE>
Now, type
<TABLE border=0 cellspacing=0 cellpadding=0>
<TR><TD ALIGN=left NOWRAP><TT> ralf/Frown/QuickStart> frown -v Tiger.lg</TT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><TT> ralf/Frown/QuickStart> hugs Tiger.hs</TT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><TT> ...</TT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><TT> Tiger> exp [ID "a", PLUS, ID "b", TIMES, INT "2"] >>= print</TT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><TT> Bin (Var "a") Add (Bin (Var "b") Mul (Int "2"))</TT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><TT> Tiger> tc "fib.tig"</TT></TD>
</TR>
<TR><TD ALIGN=left NOWRAP><TT> ...
</TT></TD>
</TR></TABLE>
The call <TT>frown -v Tiger.lg</TT> generates a Haskell parser which can then
be loaded into <TT>hugs</TT> (or <TT>ghci</TT>). The parser has type <TT>exp :: (<I>Monad</I></TT><TT> m) => [<I>Terminal</I></TT><TT>] -> m <I>Expr</I></TT>, that is, the parser is a computation that
takes a list of terminals as input and returns an expression.<BR>
<BR>
<BR>
More examples can be found in the directory <TT>Manual/Examples</TT>:
<DL CLASS="description" COMPACT=compact><DT CLASS="dt-description">
<B><TT>Paren1.lg</TT></B><DD CLASS="dd-description"><BR>
well-balanced parentheses: a pure grammar (see Sec. <A HREF="Manual004.html#sec:pure">3.2.1</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Paren2.lg</TT></B><DD CLASS="dd-description"><BR>
an extension of <TT>Paren1.lg</TT> illustrating the definition of attributes
(see Sec. <A HREF="Manual004.html#sec:attributes">3.2.2</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Calc.lg</TT></B><DD CLASS="dd-description"><BR>
a simple evaluator for arithmetic expressions: a parser that
interfaces with a separate lexer (see Sec. <A HREF="Manual004.html#sec:lexer">3.2.3</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>MCalc.lg</TT></B><DD CLASS="dd-description"><BR>
a variant of the desktop calculator (<TT>Calc.lg</TT>) that prints all
intermediate results: illustrates monadic actions (see
Sec. <A HREF="Manual004.html#sec:monadicactions">3.2.4</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Let1.lg</TT></B><DD CLASS="dd-description"><BR>
an ambiguous expression grammar: illustrates backtracking parsers (see
Sec. <A HREF="Manual004.html#sec:backtracking">3.2.5</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Let2.lg</TT></B><DD CLASS="dd-description"><BR>
an expression grammar: illustrates the use of precedences and
associativity (see Sec. <A HREF="Manual004.html#sec:prec">3.2.6</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Let3.lg</TT></B><DD CLASS="dd-description"><BR>
a variant of the expression grammar: shows how to simulate inherited
attributes using a reader monad (see Sec. <A HREF="Manual004.html#sec:reader">3.2.8</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Let4.lg</TT></B><DD CLASS="dd-description"><BR>
an expression grammar: illustrates a parser
that interfaces with a monadic lexer (see Sec. <A HREF="Manual004.html#sec:mlexer">3.3.1</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Let5.lg</TT></B><DD CLASS="dd-description"><BR>
a variant of <TT>Let4.lg</TT> with better error reporting (see
Sec. <A HREF="Manual004.html#sec:reporting">3.3.2</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Let6.lg</TT></B><DD CLASS="dd-description"><BR>
a variant of <TT>Let5.lg</TT> with even better error reporting: prints a
list of expected tokens upon error (see Sec. <A HREF="Manual004.html#sec:expected">3.3.3</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Let7.lg</TT></B><DD CLASS="dd-description"><BR>
yet another variant of the expression grammar: illustrates a simple
form of error correction (see Sec. <A HREF="Manual004.html#sec:errorcorrection">3.3.4</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Let8.lg</TT></B><DD CLASS="dd-description"><BR>
variant of <TT>Let7.lg</TT> that notifies the user of corrections (see
Sec. <A HREF="Manual004.html#sec:errorcorrection">3.3.4</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>VarCalc.lg</TT></B><DD CLASS="dd-description"><BR>
a variant of the desktop calculator (<TT>Calc.lg</TT>) that works without a
separate lexer: illustrates guards (see Sec. <A HREF="Manual004.html#sec:terminal2">3.4.2</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>Paren3.lg</TT></B><DD CLASS="dd-description"><BR>
illustrates the tracing facilities (see Sec. <A HREF="Manual004.html#sec:tracing">3.4.4</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>VarParen.lg</TT></B><DD CLASS="dd-description"><BR>
illustrates irrefutable patterns on the right-hand side of productions
(see Sec. <A HREF="Manual005.html#sec:irrefutable">4.1</A>);<BR>
<BR>
<DT CLASS="dt-description"><B><TT>RepMin.lg</TT></B><DD CLASS="dd-description"><BR>
a solution to the rep-min problem: illustrates how to simulate
inherited attributes using functional attributes (see
Sec. <A HREF="Manual005.html#sec:inherited">4.2</A>).
</DL>
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