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<H1>Tutorial on Name Analysis</H1>
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<H1><A NAME="SEC2" HREF="nametutorial_toc.html#SEC2">Basic Scope Rules</A></H1>
<P>
In many cases of name analysis the language distinguishes between
defining occurrences of identifiers in declaration and applied
occurrences in expressions (an example with only one kind of identifier
occurrence is shown below).
Hence, we extend our kernel grammar by <CODE>DefIdent</CODE> for
defining occurrences of identifiers and <CODE>UseIdent</CODE>
for applied occurrences, and by <CODE>Declarations</CODE>
that introduce names for values.
An <CODE>Expression</CODE> can be an applied identifier occurrence.
<P>
Furthermore we introduce nested <CODE>Block</CODE>s by deriving them from
<CODE>Expressions</CODE>, and hence also from <CODE>Statements</CODE>.
<P>
<B>CoreScope.con</B>[5]==
<PRE>
<TT>
Declaration: 'val' ValDecls ';'.
ValDecls: ValDecl // ','.
ValDecl: DefIdent '=' Expression.
Expression: Block.
Operand: UseIdent.
DefIdent: Ident.
UseIdent: Ident.
</TT>
</PRE>
<FONT SIZE=1>
<PRE>
This macro is attached to a product file.
</PRE>
</FONT>
<P>
The basic task of name analysis is consistent renaming.
For each identifier occurrence a <CODE>Key</CODE> attribute is computed such
that identifier occurrences that refer to the same object in the program have
the same <CODE>Key</CODE> attribute value. Hence <CODE>Key</CODE>s identify
program objects uniquely. <CODE>Key</CODE>s are used to associate properties
with program objects and to retrieve those properties in different
contexts.
<P>
The scope rules of a language determine how identifier occurrences
are bound to program objects.
<P>
The basic Algol-like scope rule reads:
<P>
<BLOCKQUOTE>
A definition of an identifier <CODE>a</CODE> is valid in the whole smallest
range that encloses that definition, except inner ranges that
contain another definition of <CODE>a</CODE>.
</BLOCKQUOTE>
<P>
Hence, a definition in an outer range is hidden by a definition
of the same identifier in an inner range for the whole inner range.
Identifiers may be applied before they are defined.
<P>
We instantiate a library module that provides computations
according to this scope rule:
<P>
<B>CoreScope.specs</B>[6]==
<PRE>
<TT>
$/Name/AlgScope.gnrc:inst
</TT>
</PRE>
<FONT SIZE=1>
<PRE>
This macro is attached to a product file.
</PRE>
</FONT>
<P>
The computational roles <CODE>RangeScope</CODE>,
<CODE>IdDefScope</CODE>, and <CODE>IdUseEnv</CODE> are associated with the corresponding
symbols of our grammar.
<P>
<B>CoreScope.lido</B>[7]==
<PRE>
<TT>
SYMBOL Block INHERITS RangeScope END;
SYMBOL DefIdent INHERITS IdDefScope, IdentOcc END;
SYMBOL UseIdent INHERITS IdUseEnv, IdentOcc END;
</TT>
</PRE>
<FONT SIZE=1>
<PRE>
This macro is attached to a product file.
</PRE>
</FONT>
<P>
As a result attributes <CODE>DefIdent.Key</CODE> and <CODE>UseIdent.Key</CODE>
are computed according to the scope rules.
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