3 files changed, 68 insertions(+), 0 deletions(-)

M include/expr.h
M src/env.c
M src/expr.c

@@ 13,6 13,7 @@ enum expression_kind {
 
 	/* Special forms */
 	EXPR_LAMBDA,
+	EXPR_PAIR,
 	EXPR_QUOTE,
 	EXPR_UNQUOTE,
 };


@@ 35,6 36,7 @@ struct expression {
 		char *symbol;
 
 		struct expression *quoted;
+		struct expression *pair[2];
 	};
 };
 

@@ 303,6 303,53 @@ env_if(struct location loc, struct list_expression *list,
 }
 
 static struct expression *
+env_cons(struct location loc, struct list_expression *list,
+	struct binding **bindings)
+{
+	if (!list || !list->next) {
+		error(loc, "Not enough arguments");
+	}
+
+	struct expression *new = mkexpression();
+	new->kind = EXPR_PAIR;
+	new->pair[0] = eval(list->expr, bindings);
+	new->pair[1] = eval(list->next->expr, bindings);
+	return new;
+}
+
+static struct expression *
+env_car(struct location loc, struct list_expression *list,
+	struct binding **bindings)
+{
+	if (!list) {
+		error(loc, "Not enough arguments");
+	}
+
+	struct expression *pair = eval(list->expr, bindings);
+	if (pair->kind != EXPR_PAIR) {
+		error(loc, "car must be used on a pair");
+	}
+
+	return expression_dup(pair->pair[0]);
+}
+
+static struct expression *
+env_cdr(struct location loc, struct list_expression *list,
+	struct binding **bindings)
+{
+	if (!list) {
+		error(loc, "Not enough arguments");
+	}
+
+	struct expression *pair = eval(list->expr, bindings);
+	if (pair->kind != EXPR_PAIR) {
+		error(loc, "cdr must be used on a pair");
+	}
+
+	return expression_dup(pair->pair[1]);
+}
+
+static struct expression *
 env_display(struct location loc, struct list_expression *list,
 	struct binding **bindings)
 {


@@ 348,6 395,10 @@ environment[] = {
 	{ .name = "define", .func = &env_define },
 	{ .name = "if",     .func = &env_if },
 
+	{ .name = "cons", .func = &env_cons },
+	{ .name = "car",  .func = &env_car },
+	{ .name = "cdr",  .func = &env_cdr },
+
 	{ .name = "display", .func = &env_display },
 	{ .name = "newline", .func = &env_newline },
 

@@ 40,6 40,10 @@ expression_dup(struct expression *expr)
 			newl = &(*newl)->next;
 		}
 		break;
+	case EXPR_PAIR:
+		new->pair[0] = expression_dup(expr->pair[0]);
+		new->pair[1] = expression_dup(expr->pair[1]);
+		break;
 	case EXPR_STRING:
 		new->string = xstrdup(expr->string);
 		break;


@@ 74,6 78,10 @@ expression_free(struct expression *expr)
 	case EXPR_UNQUOTE:
 		expression_free(expr->quoted);
 		break;
+	case EXPR_PAIR:
+		expression_free(expr->pair[0]);
+		expression_free(expr->pair[1]);
+		break;
 	case EXPR_STRING:
 		free(expr->string);
 		break;


@@ 110,6 118,13 @@ expression_print(FILE *out, struct expression *expr)
 		fputs(",", out);
 		expression_print(out, expr->quoted);
 		break;
+	case EXPR_PAIR:
+		fputs("(", out);
+		expression_print(out, expr->pair[0]);
+		fputs(" . ", out);
+		expression_print(out, expr->pair[1]);
+		fputs(")", out);
+		break;
 	case EXPR_STRING:
 		fputs("\"", out);
 		for (size_t i = 0; expr->string[i] != '\0'; i++) {