iris

commit 9539419a2015c425987e74556e2dbf94e1887af5
parent 9c7e1299c8ab117b928e3b53570b33fcdbd8c735
Author: sin <sin@2f30.org>
Date:   Wed, 14 May 2014 13:46:29 +0100

Parse pairs/lists

Diffstat:
M
lexer.c
 | 
13
+++++++++++++
M
lexer.h
 | 
1
+
M
parser.c
 | 
84
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

3 files changed, 98 insertions(+), 0 deletions(-)
diff --git a/lexer.c b/lexer.c
@@ -30,6 +30,8 @@ static enum state state;
 static char *s;
 static char *e;
 static char buf[MAXTOKSIZE];
+static struct tok lasttok;
+static int pendingtok;
 
 static int
 delim(int c)
@@ -44,6 +46,10 @@ gettok(FILE *in)
 	struct tok tok;
 	int c;
 
+	if (pendingtok == 1) {
+		pendingtok = 0;
+		return lasttok;
+	}
 again:
 	state = SSe;
 	s = e = buf;
@@ -240,3 +246,10 @@ lexeme(struct tok *t)
 		return strdup(t->s);
 	return strndup(t->s, t->e - t->s);
 }
+
+void
+pushbacktok(struct tok t)
+{
+	lasttok = t;
+	pendingtok = 1;
+}
diff --git a/lexer.h b/lexer.h
@@ -21,3 +21,4 @@ struct tok {
 
 struct tok gettok(FILE *fp);
 char *lexeme(struct tok *);
+void pushbacktok(struct tok);
diff --git a/parser.c b/parser.c
@@ -16,6 +16,8 @@ enum objtype {
 	ONumber,
 	OCharacter,
 	OString,
+	OEmptylist,
+	OPair,
 };
 
 struct object {
@@ -49,6 +51,11 @@ struct object {
 		struct {
 			char *s;
 		} s;
+		/* pair */
+		struct {
+			struct object *car;
+			struct object *cdr;
+		} p;
 	} d;
 };
 
@@ -135,6 +142,52 @@ string(char *s)
 	return o;
 }
 
+static struct object *
+emptylist(void)
+{
+	struct object *o;
+
+	o = newobject();
+	o->type = OEmptylist;
+	return o;
+}
+
+static struct object *
+cons(struct object *car, struct object *cdr)
+{
+	struct object *o;
+
+	o = newobject();
+	o->type = OPair;
+	o->d.p.car = car;
+	o->d.p.cdr = cdr;
+	return o;
+}
+
+static struct object *
+pair(FILE *in)
+{
+	struct object *car, *cdr;
+	struct tok t;
+
+	t = gettok(in);
+	if (t.type == TRparen)
+		return emptylist();
+	pushbacktok(t);
+	car = sexpression(in);
+	t = gettok(in);
+	if (t.type == TDot) {
+		cdr = sexpression(in);
+		t = gettok(in);
+		if (t.type != TRparen)
+			return error("missing right parenthesis");
+		return cons(car, cdr);
+	}
+	pushbacktok(t);
+	cdr = pair(in);
+	return cons(car, cdr);
+}
+
 struct object *
 sexpression(FILE *in)
 {
@@ -161,6 +214,8 @@ sexpression(FILE *in)
 		return character(l[2]);
 	case TString:
 		return string(l);
+	case TLparen:
+		return pair(in);
 	default:
 		return error("unhandled token");
 	}
@@ -182,6 +237,27 @@ eval(struct object *o)
 	return o;
 }
 
+static void
+printpair(struct object *o)
+{
+	struct object *car, *cdr;
+
+	car = o->d.p.car;
+	cdr = o->d.p.cdr;
+	print(car);
+	if (cdr->type == OPair) {
+		putchar(' ');
+		printpair(cdr);
+	} else if (cdr->type == OEmptylist) {
+		return;
+	} else {
+		putchar(' ');
+		putchar('.');
+		putchar(' ');
+		print(cdr);
+	}
+}
+
 void
 print(struct object *o)
 {
@@ -204,5 +280,13 @@ print(struct object *o)
 	case OString:
 		printf("%s", o->d.s.s);
 		break;
+	case OEmptylist:
+		printf("()");
+		break;
+	case OPair:
+		putchar('(');
+		printpair(o);
+		putchar(')');
+		break;
 	}
 }