Filter: The for loop uses the method system for type dispatch

filter/config.Y

@@ -1000,8 +1000,7 @@ cmd:
    { new_config->current_scope->active = 0; } term { new_config->current_scope->active = 1; }
    DO cmd {
      cf_pop_block_scope(new_config);
-     $$ = f_new_inst(FI_FOR_INIT, $6, $3);
-     $$->next = f_new_inst(FI_FOR_NEXT, $3, $9);
+     $$ = f_for_cycle($3, $6, $9);
    }
  | symbol_known '=' term ';' {
      switch ($1->class) {

filter/decl.m4

@@ -130,7 +130,7 @@ m4_ifelse($1,1,,[[FID_NEW_METHOD()m4_dnl
   struct f_inst *arg$1 = args;
   if (args == NULL) cf_error("Not enough arguments"); /* INST_NAME */
   args = args->next;
-  FID_METHOD_CALL()    , arg$1]])
+FID_METHOD_CALL()    , arg$1]])
 FID_LINEARIZE_BODY()m4_dnl
 pos = linearize(dest, whati->f$1, pos);
 FID_INTERPRET_BODY()')
@@ -230,6 +230,12 @@ FID_NEW_ARGS()m4_dnl
   , struct f_inst * f$1
 FID_NEW_BODY()m4_dnl
 whati->f$1 = f$1;
+m4_define([[INST_METHOD_NUM_ARGS]],m4_eval($1-1))m4_dnl
+FID_NEW_METHOD()m4_dnl
+  struct f_inst *arg$1 = args;
+  if (args == NULL) cf_error("Not enough arguments"); /* INST_NAME */
+  args = NULL; /* The rest is the line itself */
+FID_METHOD_CALL()    , arg$1
 FID_DUMP_BODY()m4_dnl
 f_dump_line(item->fl$1, indent + 1);
 FID_LINEARIZE_BODY()m4_dnl

filter/f-inst.c

@@ -569,92 +569,63 @@
     RESULT(T_LCLIST, ad, &null_adata);
   }
 
-  INST(FI_FOR_INIT, 1, 0) {
+  /* Common loop begin instruction, always created by f_for_cycle() */
+  INST(FI_FOR_LOOP_START, 0, 3) {
     NEVER_CONSTANT;
-    ARG_ANY(1);
     SYMBOL;
 
-    FID_NEW_BODY()
-    ASSERT((sym->class & ~0xff) == SYM_VARIABLE);
+    /* Repeat the instruction which called us */
+    ASSERT_DIE(fstk->ecnt > 1);
+    prevline.pos--;
 
-    /* Static type check */
-    if (f1->type)
-    {
-      enum f_type t_var = (sym->class & 0xff);
-      enum f_type t_arg = f_type_element_type(f1->type);
-      if (!t_arg)
-        cf_error("Value of expression in FOR must be iterable, got %s",
-		 f_type_name(f1->type));
-      if (t_var != t_arg)
-	cf_error("Loop variable '%s' in FOR must be %s, is %s",
-		 sym->name, f_type_name(t_arg), f_type_name(t_var));
-    }
+    /* There should be exactly three items on the value stack to be taken care of */
+    fstk->vcnt += 3;
 
-    FID_INTERPRET_BODY()
+    /* And these should also stay there after we finish for the caller instruction */
+    curline.ventry += 3;
 
-    /* Dynamic type check */
-    if ((sym->class & 0xff) != f_type_element_type(v1.type))
-      runtime("Mismatched argument and variable type");
+    /* Assert the iterator variable positioning */
+    ASSERT_DIE(curline.vbase + sym->offset == fstk->vcnt - 1);
 
-    /* Setup the index */
-    v2 = (struct f_val) { .type = T_INT, .val.i = 0 };
-
-    /* Keep v1 and v2 on the stack */
-    fstk->vcnt += 2;
+    /* The result type declaration makes no sense here but is needed */
+    RESULT_TYPE(T_VOID);
   }
 
-  INST(FI_FOR_NEXT, 2, 0) {
+  /* Type-specific for_next iterators */
+  INST(FI_PATH_FOR_NEXT, 3, 0) {
     NEVER_CONSTANT;
-    SYMBOL;
+    ARG(1, T_PATH);
+    if (as_path_walk(v1.val.ad, &v2.val.i, &v3.val.i))
+      LINE(2,0);
 
-    /* Type checks are done in FI_FOR_INIT */
+    METHOD_CONSTRUCTOR("!for_next");
+  }
 
-    /* Loop variable */
-    struct f_val *var = &fstk->vstk[curline.vbase + sym->offset];
-    int step = 0;
+  INST(FI_CLIST_FOR_NEXT, 3, 0) {
+    NEVER_CONSTANT;
+    ARG(1, T_CLIST);
+    if (int_set_walk(v1.val.ad, &v2.val.i, &v3.val.i))
+      LINE(2,0);
 
-    switch(v1.type)
-    {
-    case T_PATH:
-      var->type = T_INT;
-      step = as_path_walk(v1.val.ad, &v2.val.i, &var->val.i);
-      break;
+    METHOD_CONSTRUCTOR("!for_next");
+  }
 
-    case T_CLIST:
-      var->type = T_PAIR;
-      step = int_set_walk(v1.val.ad, &v2.val.i, &var->val.i);
-      break;
+  INST(FI_ECLIST_FOR_NEXT, 3, 0) {
+    NEVER_CONSTANT;
+    ARG(1, T_ECLIST);
+    if (ec_set_walk(v1.val.ad, &v2.val.i, &v3.val.ec))
+      LINE(2,0);
 
-    case T_ECLIST:
-      var->type = T_EC;
-      step = ec_set_walk(v1.val.ad, &v2.val.i, &var->val.ec);
-      break;
+    METHOD_CONSTRUCTOR("!for_next");
+  }
 
-    case T_LCLIST:
-      var->type = T_LC;
-      step = lc_set_walk(v1.val.ad, &v2.val.i, &var->val.lc);
-      break;
+  INST(FI_LCLIST_FOR_NEXT, 3, 0) {
+    NEVER_CONSTANT;
+    ARG(1, T_LCLIST);
+    if (lc_set_walk(v1.val.ad, &v2.val.i, &v3.val.lc))
+      LINE(2,0);
 
-    default:
-      runtime( "Clist or lclist expected" );
-    }
-
-    if (step)
-    {
-      /* Keep v1 and v2 on the stack */
-      fstk->vcnt += 2;
-
-      /* Repeat this instruction */
-      curline.pos--;
-
-      /* Execute the loop body */
-      LINE(1, 0);
-
-      /* Space for loop variable, may be unused */
-      fstk->vcnt += 1;
-    }
-    else
-      var->type = T_VOID;
+    METHOD_CONSTRUCTOR("!for_next");
   }
 
   INST(FI_CONDITION, 1, 0) {

filter/f-inst.h

@@ -95,6 +95,8 @@ void f_add_lines(const struct f_line_item *what, struct filter_iterator *fit);
 
 
 struct filter *f_new_where(struct f_inst *);
+struct f_inst *f_for_cycle(struct symbol *var, struct f_inst *term, struct f_inst *block);
+
 static inline struct f_dynamic_attr f_new_dynamic_attr(u8 type, enum f_type f_type, uint code) /* Type as core knows it, type as filters know it, and code of dynamic attribute */
 { return (struct f_dynamic_attr) { .type = type, .f_type = f_type, .ea_code = code }; }   /* f_type currently unused; will be handy for static type checking */
 static inline struct f_dynamic_attr f_new_dynamic_attr_bit(u8 bit, enum f_type f_type, uint code) /* Type as core knows it, type as filters know it, and code of dynamic attribute */

filter/f-util.c

@@ -41,6 +41,40 @@ struct filter *f_new_where(struct f_inst *where)
   return f;
 }
 
+struct f_inst *
+f_for_cycle(struct symbol *var, struct f_inst *term, struct f_inst *block)
+{
+  ASSERT((var->class & ~0xff) == SYM_VARIABLE);
+  ASSERT(term->next == NULL);
+
+  /* Static type check */
+  if (term->type == T_VOID)
+    cf_error("Couldn't infer the type of FOR expression, please assign it to a variable.");
+
+  enum f_type el_type = f_type_element_type(term->type);
+  struct sym_scope *scope = el_type ? f_type_method_scope(term->type) : NULL;
+  struct symbol *ms = scope ? cf_find_symbol_scope(scope, "!for_next") : NULL;
+
+  if (!ms)
+    cf_error("Type %s is not iterable, can't be used in FOR", f_type_name(term->type));
+
+  if (var->class != (SYM_VARIABLE | el_type))
+    cf_error("Loop variable '%s' in FOR must be of type %s, got %s",
+	var->name, f_type_name(el_type), f_type_name(var->class & 0xff));
+
+  /* Push the iterator auxiliary value onto stack */
+  struct f_inst *iter = term->next = f_new_inst(FI_CONSTANT, (struct f_val) {});
+
+  /* Initialize the iterator variable */
+  iter->next = f_new_inst(FI_CONSTANT, (struct f_val) { .type = el_type });
+
+  /* Prepend the loop block with loop beginning instruction */
+  struct f_inst *loop_start = f_new_inst(FI_FOR_LOOP_START, var);
+  loop_start->next = block;
+
+  return ms->method->new_inst(term, loop_start);
+}
+
 #define CA_KEY(n)	n->name, n->fda.type
 #define CA_NEXT(n)	n->next
 #define CA_EQ(na,ta,nb,tb)	(!strcmp(na,nb) && (ta == tb))

filter/filter.c

@@ -174,6 +174,7 @@ interpret(struct filter_state *fs, const struct f_line *line, struct f_val *val)
   fstk->estk[0].pos = 0;
 
 #define curline fstk->estk[fstk->ecnt-1]
+#define prevline fstk->estk[fstk->ecnt-2]
 
 #ifdef LOCAL_DEBUG
   debug("Interpreting line.");