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 97fa31173ea8e55cda1d852f667237723fa81cff..9e1ce020eb7ff0b265938b5f76b525244131128c 100644 (file)
--- 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.