* expression is expected, a 'Bad expression' error is signalled. */
static const char s_bad_expression[] = "Bad expression";
+/* Case or cond expressions must have at least one clause. If a case or cond
+ * expression without any clauses is detected, a 'Missing clauses' error is
+ * signalled. */
+static const char s_missing_clauses[] = "Missing clauses";
+
+/* If a case clause is detected that is not in the format
+ * (<label(s)> <expression1> <expression2> ...)
+ * a 'Bad case clause' error is signalled. */
+static const char s_bad_case_clause[] = "Bad case clause";
+
+/* If there is an 'else' clause in a case statement, it must be the last
+ * clause. If after the 'else' case clause further clauses are detected, an
+ * 'Extra case clause' error is signalled. */
+static const char s_extra_case_clause[] = "Extra case clause";
+
+/* If a case clause is detected where the <label(s)> element is neither a
+ * proper list nor (in case of the last clause) the syntactic keyword 'else',
+ * a 'Bad case labels' error is signalled. Note: If you encounter this error
+ * for an else-clause which seems to be syntactically correct, check if 'else'
+ * is really a syntactic keyword in that context. If 'else' is bound in the
+ * local or global environment, it is not considered a syntactic keyword, but
+ * will be treated as any other variable. */
+static const char s_bad_case_labels[] = "Bad case labels";
+
+/* In a case statement all labels have to be distinct. If in a case statement
+ * a label occurs more than once, a 'Duplicate case label' error is
+ * signalled. */
+static const char s_duplicate_case_label[] = "Duplicate case label";
+
/* Signal a syntax error. We distinguish between the form that caused the
* error and the enclosing expression. The error message will print out as
return loc;
}
+/* Return true if the symbol is - from the point of view of a macro
+ * transformer - a literal in the sense specified in chapter "pattern
+ * language" of R5RS. In the code below, however, we don't match the
+ * definition of R5RS exactly: It returns true if the identifier has no
+ * binding or if it is a syntactic keyword. */
+static int
+literal_p (const SCM symbol, const SCM env)
+{
+ const SCM x = scm_cons (symbol, SCM_UNDEFINED);
+ const SCM value = *scm_lookupcar (x, env, 0);
+ if (SCM_UNBNDP (value) || SCM_MACROP (value))
+ return 1;
+ else
+ return 0;
+}
+
#define unmemocar scm_unmemocar
SCM_SYMBOL (sym_three_question_marks, "???");
SCM_GLOBAL_SYMBOL (scm_sym_begin, s_begin);
SCM
-scm_m_begin (SCM xorig, SCM env SCM_UNUSED)
+scm_m_begin (SCM expr, SCM env SCM_UNUSED)
{
- SCM_ASSYNT (scm_ilength (SCM_CDR (xorig)) >= 0, s_expression, s_begin);
- return scm_cons (SCM_IM_BEGIN, SCM_CDR (xorig));
+ const SCM cdr_expr = SCM_CDR (expr);
+
+ ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
+
+ SCM_SETCAR (expr, SCM_IM_BEGIN);
+ return expr;
}
SCM_GLOBAL_SYMBOL (scm_sym_case, s_case);
SCM
-scm_m_case (SCM xorig, SCM env SCM_UNUSED)
+scm_m_case (SCM expr, SCM env)
{
SCM clauses;
- SCM cdrx = SCM_CDR (xorig);
- SCM_ASSYNT (scm_ilength (cdrx) >= 2, s_clauses, s_case);
- clauses = SCM_CDR (cdrx);
+ SCM all_labels = SCM_EOL;
+
+ /* Check, whether 'else is a literal, i. e. not bound to a value. */
+ const int else_literal_p = literal_p (scm_sym_else, env);
+
+ const SCM cdr_expr = SCM_CDR (expr);
+ ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
+ ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 2, s_missing_clauses, expr);
+
+ clauses = SCM_CDR (cdr_expr);
while (!SCM_NULLP (clauses))
{
- SCM clause = SCM_CAR (clauses);
- SCM_ASSYNT (scm_ilength (clause) >= 2, s_clauses, s_case);
- SCM_ASSYNT (scm_ilength (SCM_CAR (clause)) >= 0
- || (SCM_EQ_P (scm_sym_else, SCM_CAR (clause))
- && SCM_NULLP (SCM_CDR (clauses))),
- s_clauses, s_case);
+ SCM labels;
+
+ const SCM clause = SCM_CAR (clauses);
+ ASSERT_SYNTAX_2 (scm_ilength (clause) >= 2,
+ s_bad_case_clause, clause, expr);
+
+ labels = SCM_CAR (clause);
+ if (SCM_CONSP (labels))
+ {
+ ASSERT_SYNTAX_2 (scm_ilength (labels) >= 0,
+ s_bad_case_labels, labels, expr);
+ all_labels = scm_append_x (scm_list_2 (labels, all_labels));
+ }
+ else
+ {
+ ASSERT_SYNTAX_2 (SCM_EQ_P (labels, scm_sym_else) && else_literal_p,
+ s_bad_case_labels, labels, expr);
+ ASSERT_SYNTAX_2 (SCM_NULLP (SCM_CDR (clauses)),
+ s_extra_case_clause, SCM_CDR (clauses), expr);
+ }
+
+ /* build the new clause */
+ if (SCM_EQ_P (labels, scm_sym_else))
+ SCM_SETCAR (clause, SCM_IM_ELSE);
+
clauses = SCM_CDR (clauses);
}
- return scm_cons (SCM_IM_CASE, cdrx);
+
+ /* Check whether all case labels are distinct. */
+ for (; !SCM_NULLP (all_labels); all_labels = SCM_CDR (all_labels))
+ {
+ const SCM label = SCM_CAR (all_labels);
+ SCM label_idx = SCM_CDR (all_labels);
+ for (; !SCM_NULLP (label_idx); label_idx = SCM_CDR (label_idx))
+ {
+ ASSERT_SYNTAX_2 (!SCM_EQ_P (SCM_CAR (label_idx), label),
+ s_duplicate_case_label, label, expr);
+ }
+ }
+
+ SCM_SETCAR (expr, SCM_IM_CASE);
+ return expr;
}
case (SCM_ISYMNUM (SCM_IM_CALL_WITH_VALUES)):
ls = z = scm_cons (scm_sym_at_call_with_values, SCM_UNSPECIFIED);
goto loop;
+ case (SCM_ISYMNUM (SCM_IM_ELSE)):
+ ls = z = scm_cons (scm_sym_else, SCM_UNSPECIFIED);
+ goto loop;
default:
/* appease the Sun compiler god: */ ;
}
{
SCM clause = SCM_CAR (x);
SCM labels = SCM_CAR (clause);
- if (SCM_EQ_P (labels, scm_sym_else))
+ if (SCM_EQ_P (labels, SCM_IM_ELSE))
{
x = SCM_CDR (clause);
PREP_APPLY (SCM_UNDEFINED, SCM_EOL);
HCoop / bpt / guile.git / blobdiff