+## ------------------------ ##
+## Pure/impure interfaces. ##
+## ------------------------ ##
+
+
+# b4_lex_param
+# ------------
+# Accumule in b4_lex_param all the yylex arguments.
+# Yes, this is quite ugly...
+m4_define([b4_lex_param],
+m4_dquote(b4_pure_if([[[[YYSTYPE *]], [[yylvalp]]][]dnl
+b4_location_if([, [[YYLTYPE *], [yyllocp]]])])dnl
+m4_ifdef([b4_lex_param], [, ]b4_lex_param)))
+
+
+# b4_user_formals
+# ---------------
+m4_define([b4_user_formals],
+[m4_ifset([b4_parse_param], [, b4_c_ansi_formals(b4_parse_param)])])
+
+
+# b4_yyerror_args
+# ---------------
+# Arguments passed to yyerror: user args plus yylloc.
+m4_define([b4_yyerror_args],
+[b4_pure_if([b4_location_if([yylocp, ])])dnl
+m4_ifset([b4_parse_param], [b4_c_args(b4_parse_param), ])])
+
+
+# b4_lyyerror_args
+# ----------------
+# Same as above, but on the lookahead, hence yyllocp instead of yylocp.
+m4_define([b4_lyyerror_args],
+[b4_pure_if([b4_location_if([yyllocp, ])])dnl
+m4_ifset([b4_parse_param], [b4_c_args(b4_parse_param), ])])
+
+
+# b4_pure_args
+# ------------
+# Arguments needed by yyerror: user args plus yylloc.
+m4_define([b4_pure_args],
+[b4_pure_if([b4_location_if([, yylocp])])[]b4_user_args])
+
+
+# b4_pure_formals
+# ---------------
+# Arguments passed to yyerror: user formals plus yyllocp.
+m4_define([b4_pure_formals],
+[b4_pure_if([b4_location_if([, YYLTYPE *yylocp])])[]b4_user_formals])
+
+
+# b4_lpure_args
+# -------------
+# Same as above, but on the lookahead, hence yyllocp instead of yylocp.
+m4_define([b4_lpure_args],
+[b4_pure_if([b4_location_if([, yyllocp])])[]b4_user_args])
+
+
+# b4_lpure_formals
+# ----------------
+# Same as above, but on the lookahead, hence yyllocp instead of yylocp.
+m4_define([b4_lpure_formals],
+[b4_pure_if([b4_location_if([YYLTYPE *yyllocp])])[]b4_user_formals])
+
+