From: NeilBrown <neil@brown.name>
Date: Tue, 30 Apr 2019 06:24:09 +0000 (+1000)
Subject: oceani: add some support for lvalues.
X-Git-Tag: JamisonCreek-3~31
X-Git-Url: https://ocean-lang.org/code/?p=ocean;a=commitdiff_plain;h=f4b24ac2cd27f5ee0e370063509f154f1e5646bf

oceani: add some support for lvalues.

New linterp_exec() returns an lvalue, (pointer to value)
and individual cases can provide either an lvalue or an rvalue.

This means the RHS of assignment might not be a simple variable,
so we leave the "v = v->merged" part to the "interp exec" for Xvar.
Also, linterp_exec() might return NULL, so be careful.
This might happen, e.g., when an array index is out of bounds.

Signed-off-by: NeilBrown <neil@brown.name>
---

diff --git a/csrc/oceani.mdc b/csrc/oceani.mdc
index 97fa311..9e1ce02 100644
--- a/csrc/oceani.mdc
+++ b/csrc/oceani.mdc
@@ -1459,18 +1459,45 @@ Each `exec` can return a value, which may be `Tnone` but must be non-NULL;
 
 ###### core functions
 
+	struct lrval {
+		struct value val, *lval;
+	};
+
+	static struct lrval _interp_exec(struct exec *e);
+
 	static struct value interp_exec(struct exec *e)
 	{
-		struct value rv;
+		struct lrval ret = _interp_exec(e);
+
+		if (ret.lval)
+			return dup_value(*ret.lval);
+		else
+			return ret.val;
+	}
+
+	static struct value *linterp_exec(struct exec *e)
+	{
+		struct lrval ret = _interp_exec(e);
+
+		return ret.lval;
+	}
+
+	static struct lrval _interp_exec(struct exec *e)
+	{
+		struct lrval ret;
+		struct value rv, *lrv = NULL;
 		rv.type = Tnone;
-		if (!e)
-			return rv;
+		if (!e) {
+			ret.lval = lrv;
+			ret.val = rv;
+			return ret;
+		}
 
 		switch(e->type) {
 		case Xbinode:
 		{
 			struct binode *b = cast(binode, e);
-			struct value left, right;
+			struct value left, right, *lleft;
 			left.type = right.type = Tnone;
 			switch (b->op) {
 			## interp binode cases
@@ -1480,7 +1507,9 @@ Each `exec` can return a value, which may be `Tnone` but must be non-NULL;
 		}
 		## interp exec cases
 		}
-		return rv;
+		ret.lval = lrv;
+		ret.val = rv;
+		return ret;
 	}
 
 ## Language elements
@@ -1579,7 +1608,8 @@ an executable.
 
 ###### interp exec cases
 	case Xval:
-		return dup_value(cast(val, e)->val);
+		rv = dup_value(cast(val, e)->val);
+		break;
 
 ###### ast functions
 	static void free_val(struct val *v)
@@ -1801,7 +1831,8 @@ link to find the primary instance.
 
 		if (v->merged)
 			v = v->merged;
-		return dup_value(v->val);
+		lrv = &v->val;
+		break;
 	}
 
 ###### ast functions
@@ -2597,16 +2628,15 @@ it is declared, and error will be raised as the name is created as
 ###### interp binode cases
 
 	case Assign:
-	{
-		struct variable *v = cast(var, b->left)->var;
-		if (v->merged)
-			v = v->merged;
+		lleft = linterp_exec(b->left);
 		right = interp_exec(b->right);
-		free_value(v->val);
-		v->val = right;
+		if (lleft) {
+			free_value(*lleft);
+			*lleft = right;
+		} else
+			free_value(right);
 		right.type = NULL;
 		break;
-	}
 
 	case Declare:
 	{
@@ -3113,10 +3143,10 @@ defined.
 				interp_exec(c->dopart);
 
 			if (c->thenpart) {
-				v = interp_exec(c->thenpart);
-				if (v.type != Tnone || !c->dopart)
-					return v;
-				free_value(v);
+				rv = interp_exec(c->thenpart);
+				if (rv.type != Tnone || !c->dopart)
+					goto Xcond_done;
+				free_value(rv);
 			}
 		} while (c->dopart);
 
@@ -3125,15 +3155,18 @@ defined.
 			if (value_cmp(v, cnd) == 0) {
 				free_value(v);
 				free_value(cnd);
-				return interp_exec(cp->action);
+				rv = interp_exec(cp->action);
+				goto Xcond_done;
 			}
 			free_value(v);
 		}
 		free_value(cnd);
 		if (c->elsepart)
-			return interp_exec(c->elsepart);
-		v.type = Tnone;
-		return v;
+			rv = interp_exec(c->elsepart);
+		else
+			rv.type = Tnone;
+	Xcond_done:
+		break;
 	}
 
 ### Finally the whole program.