1 files changed, 134 insertions, 0 deletions
diff --git a/s2/rhoc.y b/s2/rhoc.y
new file mode 100644
index 0000000..63f0b9c
--- /dev/null
+++ b/s2/rhoc.y
@@ -0,0 +1,134 @@
+%{
+double mem[26];
+%}
+%union {
+	double val;
+	int idx;
+}
+%token	<val> NUMBER
+%token	<idx> VAR
+%type	<val> expr
+%right	'='
+%left	'+' '-'
+%left	'*' '/'
+%left	UNMIN
+%%
+list:	/* ε */
+	| list '\n'
+	| list expr '\n'	{ print("\t%.8g\n", $2); }
+	| list expr ';'		{ print("\t%.8g\n", $2); }
+	| list error '\n'	{ yyerrok; }
+	;
+expr:	  NUMBER
+	| VAR			{ $$ = mem[$1]; }
+	| VAR '=' expr		{ $$ = mem[$1] = $3; }
+	| '-' expr	%prec UNMIN { $$ = -$2; }
+	| expr '+' expr		{ $$ = $1 + $3; }
+	| expr '-' expr 	{ $$ = $1 - $3; }
+	| expr '*' expr 	{ $$ = $1 * $3; }
+	| expr '/' expr
+	{
+		if($3 == 0)
+			rterror("division by zero");
+		$$ = $1 / $3;
+	}
+	| expr '%' expr 	{ $$ = fmod($1, $3); }
+	| expr '(' expr ')'	{ $$ = $1 * $3; }
+	| '(' expr ')'		{ $$ = $2; }
+	;
+%%
+#include <u.h>
+#include <libc.h>
+#include <ctype.h>
+#include <bio.h>
+
+Biobuf *bin;
+jmp_buf begin;
+int lineno;
+int prompt;
+
+int yyparse(void);
+
+void
+error(char *msg, int ln)
+{
+	fprint(2, "%s at line %d\n", msg, ln);
+}
+
+void
+yyerror(char *msg)
+{
+	error(msg, lineno);
+}
+
+int
+yylex(void)
+{
+	int c;
+
+	if(prompt){
+		print("%d: ", lineno);
+		prompt--;
+	}
+	while((c = Bgetc(bin)) == ' ' || c == '\t')
+		;
+	if(c == '.' || isdigit(c)){
+		Bungetc(bin);
+		Bgetd(bin, &yylval.val);
+		return NUMBER;
+	}
+	if(islower(c)){
+		yylval.idx = c - 'a';
+		return VAR;
+	}
+	if(c == '\n'){
+		lineno++;
+		prompt++;
+	}
+	return c;
+}
+
+void
+rterror(char *msg)
+{
+	error(msg, lineno-1);
+	longjmp(begin, 0);
+}
+
+int
+catch(void *ureg, char *msg)
+{
+	if(strncmp(msg, "sys: fp", 7) == 0){
+		error("floating point exception", lineno-1);
+		notejmp(ureg, begin, 0);
+	}
+	return 0;
+}
+
+void
+usage(void)
+{
+	fprint(2, "usage: %s\n", argv0);
+	exits("usage");
+}
+
+void
+main(int argc, char *argv[])
+{
+	ARGBEGIN{
+	default: usage();
+	}ARGEND;
+
+	if(argc > 0)
+		usage();
+	bin = Bfdopen(0, OREAD);
+	if(bin == nil)
+		sysfatal("Bfdopen: %r");
+	lineno++;
+	prompt++;
+	setjmp(begin);
+	atnotify(catch, 1);
+	yyparse();
+	Bterm(bin);
+	exits(0);
+}