From 7a643120366f1ea24eac5ccb759d4df616e7789b Mon Sep 17 00:00:00 2001
From: Toby Goodwin <toby@paccrat.org>
Date: Mon, 19 Mar 2018 20:55:56 +0000
Subject: implement desugaring version (again, lost due to git problem)

---
 tree.c | 47 ++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 40 insertions(+), 7 deletions(-)

(limited to 'tree.c')

diff --git a/tree.c b/tree.c
index 6a79bbc..d167a7c 100644
--- a/tree.c
+++ b/tree.c
@@ -2,9 +2,47 @@
 
 #include "rc.h"
 
+/* convert if followed by ifnot to else */
+static Node *desugar_ifnot(Node *n) {
+	if (n->type == nBody && n->u[1].p && n->u[1].p->type == nIfnot) {
+		/* (body (if c x) (if-not y)) => (body (if c (else x y))) */
+		if (n->u[0].p->type == nIf) {
+			Node *yes = n->u[0].p;
+			Node *no = n->u[1].p;
+			Node *els = nalloc(offsetof(Node, u[2]));
+			els->type = nElse;
+			els->u[1].p = no->u[0].p;
+			els->u[0].p = yes->u[1].p;
+			yes->u[1].p = els;
+			n->u[1].p = NULL;
+		} else goto fail;
+	} else if (n->type == nBody &&
+			n->u[1].p && n->u[1].p->type == nBody &&
+			n->u[1].p->u[0].p &&
+				n->u[1].p->u[0].p->type == nIfnot) {
+		/* (body (if c x) (body (if-not y) z)) =>
+			(body (if c (else x y)) z) */
+		if (n->u[0].p->type == nIf) {
+			Node *yes = n->u[0].p;
+			Node *no = n->u[1].p->u[0].p;
+			Node *els = nalloc(offsetof(Node, u[2]));
+			els->type = nElse;
+                        els->u[1].p = no->u[0].p;
+                        els->u[0].p = yes->u[1].p;
+                        yes->u[1].p = els;
+                        n->u[1].p = n->u[1].p->u[1].p;
+		} else goto fail;
+	}
+
+	return n;
+fail:
+	rc_error("`if not' must follow `if'");
+	return NULL;
+}
+
 /* make a new node, pass it back to yyparse. Used to generate the parsetree. */
 
-extern Node *mk(int /*nodetype*/ t,...) {
+extern Node *mk(enum nodetype t,...) {
 	va_list ap;
 	Node *n;
 	va_start(ap, t);
@@ -60,13 +98,8 @@ extern Node *mk(int /*nodetype*/ t,...) {
 		break;
  	}
 	n->type = t;
-        if (t == nBody && n->u[1].p && n->u[1].p->type == nIfnot) {
-                if (n->u[0].p->type == nIf) {
-                        fprint(2, "here i am!\n");
-                } else
-                        rc_error("`if not' must follow `if'");
 
-        }
+	n = desugar_ifnot(n);
 	va_end(ap);
 	return n;
 }
-- 
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