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doc/pascal/hints.doc

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+.sp 1.5i
+.nr H1 7
+.NH
+Hints to change the standard
+.nh
+.sp
+.LP
+We encoutered some difficulties when the compiler was developed. In this
+chapter some hints are presented to change the standard, which would make
+the implementation of the compiler less difficult. The semantics of Pascal
+would not be altered by these adaptions.
+.sp 2
+.LP
+\- Some minor changes in the grammar of Pascal from the user's point of view,
+but which make the writing of an LL(1) parser considerably easier, could be:
+.in +3m
+.nf
+field-list   : [ ( fixed-part [ variant-part ] | variant-part ) ] .
+fixed-part   : record-section \fB;\fR { record-section \fB;\fR } .
+variant-part : \fBcase\fR variant-selector \fBof\fR variant \fB;\fR { variant \fB;\fR } .
+
+case-statement : \fBcase\fR case-index \fBof\fR case-list-element \fB;\fR { case-list-element \fB;\fR } \fBend\fR .
+.fi
+.in -3m
+
+
+.LP
+\- To ease the semantic checking on sets, the principle of qualified sets could
+be used, every set-constructor must be preceeded by its type-identifier:
+.nf
+.ti +3m
+set-constructor : type-identifier \fB[\fR [ member-designator { \fB,\fR member-designator } ] \fB]\fR .
+
+Example:
+	t1 = set of 1..5;
+	t2 = set of integer;
+
+The type of [3, 5] would be ambiguous, but the type of t1[3, 5] not.
+.fi
+
+
+.LP
+\- Another problem arises from the fact that a function name can appear in
+three distinct 'use' contexts: function call, assignment of function
+result and as function parameter.
+.br
+Example:
+.in +5m
+.nf
+\fBprogram\fR function_name;
+
+\fBfunction\fR p(x : integer; function y : integer) : integer;
+\fBbegin\fR .. \fBend\fR;
+
+\fBfunction\fR f : integer;
+\fBbegin\fR
+        f := p(f, f);     (*)
+\fBend\fR;
+
+\fBbegin\fR .. \fBend\fR.
+.fi
+.in -5m
+
+A possible solution in case of a call (also a procedure call) would be to
+make the (possibly empty) actual-parameter-list mandatory. The assignment
+of the function result could be changed in a \fIreturn\fR statement.
+Though this would change the semantics of the program slightly.
+.br
+The above statement (*) would look like this: return p(f(), f);
+
+
+.LP
+\- Another extension to the standard could be the implementation of an
+\fIotherwise\fR clause in a case-statement. This would behave exactly like
+the \fIdefault\fR clause in a switch-statement in C.
+.bp