I've been struggling with this little issue for a while. I am trying to create my own implementation of an internal JSON structure. The challenge is that with Ada I have to use an access type to make it recursive and access types have the risk of leaking if I don't have it tightly controlled. In order to make it controlled, I kept all the real activity private I provided Get (Source:...) and Set (Target:...; Value:...) functions/procedures for the Node type that will attempt to verify and handle any existing Vector (json-array) or Map (json-object) elements. In order to further ensure that I was using stable features of Ada 2012 and catching contents as they go out of scope, I tried to use a Protected_Controlled type and "managing" Ada libraries, but found that the container libraries couldn't handle protected types, so I used simply Controlled. The Finalize (...) procedure is for any Vector or Map types and recursively frees the Node_Value.Reference.
My question is if I am applying Ada 2012 correctly, or else how do I create a memory managed recursion of a type that could be either a vector/map or a string/number?
private
...
type Node_Access is access Node;
type Node_Value is new Ada.Finalization.Controlled with record
Reference : Node_Access;
end record;
overriding procedure Initialize (Item : in out Node_Value);
overriding procedure Adjust (Item : in out Node_Value);
overriding procedure Finalize (Item : in out Node_Value);
...
package Of_Array is new Ada.Containers.Indefinite_Vectors (Natural, Node_Value);
package Of_Object is new Ada.Containers.Indefinite_Ordered_Maps (Wide_String, Node_Value);
type Node is record
...
Vector : aliased Of_Array.Vector;
Object : aliased Of_Object.Map;
end record
with Size => 96;
procedure Free is new Ada.Unchecked_Deallocation (Node, Node_Access);
The way to do it (in my opinion) is to use OOP and have an abstract element as the root node of a family of types representing the different kinds of data which can be stored.
An array of elements can then be implemented as a vector of the class rooted at the abstract element type. An "object" can be implemented as a hash-table with a string key and the class rooted at the abstract element type as the values.
Self-referential types without access types are a valid use for type extension in combination with an indefinite container. A simple example is S-expressions, or Sexes. A Sex is either an atom or a list of zero or more Sexes. The right way to be able to do this would be
with Ada.Containers.Indefinite_Vectors;
package Sexes is
type Sex is private;
-- Operations on Sex
private -- Sexes
package Sex_List is new Ada.Containers.Indefinite_Vectors
(Index_Type => Positive, Element_Type => Sex); -- Illegal
type Sex (Is_Atom : Boolean := False) is record
case Is_Atom is
when False =>
Value : Atom;
when True =>
List : Sex_List.Vector;
end case;
end record;
end Sexes;
but Ada doesn't allow this. We can use type extension to get around this:
private -- Sexes
type Root is tagged null record;
package Sex_List is new Ada.Containers.Indefinite_Vectors
(Index_Type => Positive, Element_Type => Root'Class);
type Sex (Is_Atom : Boolean := False) is new Root with record
case Is_Atom is
when False =>
Value : Atom;
when True =>
List : Sex_List.Vector;
end case;
end record;
end Sexes;
which is legal. The only catch is that you have to convert anything taken from List to Sex (or Node in your case).
HTH; sorry about the late response.
Related
I've just started learning Ada and I cannot figure out how to keep the program running when the user input is beyond the declared range of a variable. I'd like to print info about bad range of input and then ask user for input again.
This is my simple code:
with Ada.Text_IO;
use Ada.Text_IO;
procedure Main is
type Score is range 0..100;
a : Score;
begin
Put_Line ("Enter value range 0-100: ");
a := Score'Value(Get_Line);
if a'Valid then
Put_Line ("You entered" & Score'Image (a));
else
Put_Line ("Bad range of input");
end if;
end Main;
Shouldn't I use the "range" in order to check the input, but rather some if's with >, < restrictions?
My other approach was to try this with exceptions, but it also doesn't work as I want it to:
with Ada.Text_IO;
with Ada.IO_Exceptions;
use Ada.Text_IO;
procedure Main is
type Score is range 0..100;
a : Score;
begin
loop
begin
Put_Line ("Enter value range 0-100: ");
a := Score'Value(Get_Line);
Put_Line ("You entered" & Score'Image (a));
exit;
exception
when Ada.IO_Exceptions.Data_Error =>
Put_Line("Bad range of input");
end;
end loop;
end Main;
I believe the problem is in my lack of understanding this language, but I hope there is some kind of easy solution for this, thanks for any help.
Now you know a magical incantation that works, but I doubt you understand why it works, or why your other incantations didn't work. I will go into painful pedagogical detail about that, in hopes that some of it might be useful or of interest.
In Ada, when you declare a type, the type is anonymous, and the name (Score) you give is the name of the first-named subtype. The first-named subtype may have constraints that don't apply to the anonymous base type. For some types, including integer types, it's possible to refer to the anonymous base type with 'Base.
Since you declared Score using range, it is a signed integer type and its base type is (roughly) symmetrical around zero. So your declaration is equivalent to something like
type Score'Base is range -128 .. 127;
subtype Score is Score'Base range 0 .. 100;
(this is not Ada and will not compile).
Score'Value returns a value of Score'Base (ARM 3.5 (53)), so if you input "101" or "-3", Score'Value will succeed and return the appropriate value. When you assign that value to your variable of subtype Score, a check is performed that the value is in the range of Score; when that fails, Constraint_Error is raised. If you input an invalid image, such as "200" or "xyz", Score'Value fails and raises Constraint_Error. So you have two kinds of incorrect input resulting in two different failures, both of which happen to raise the same exception.
Your first version failed because you never got to the if statement. Your second version failed because Ada.Text_IO.Get_Line never raises Data_Error.
When dealing with numeric input, I advise that a complete line be read into a String and you then parse out the value(s) from that String, as you have done. However, 'Value will reject some input that you might want to consider valid. For example, you might want to accept "23 skidoo" and get the value 23 from it. For that, you might want to instantiate Ada.Text_IO.Integer_IO for your numeric (sub)type and use the Get function that takes a String parameter:
package Score_IO is new Ada.Text_IO.Integer_IO (Num => Score);
...
Score_IO.Get (From => "23 skidoo", Item => A, Last => Last);
will set A to 23 and Last to the index of '3' in From (2).
HTH
I've been learning lua and can't seem to make a simple implementation of this binary tree work...
function createTree(tree, max)
if max > 0 then
tree = {data = max, left = {}, right = {}}
createTree(tree.left, max - 1)
createTree(tree.right, max - 1)
end
end
function printTree(tree)
if tree then
print(tree.data)
printTree(tree.left)
printTree(tree.right)
end
end
tree = {}
createTree(tree, 3)
printTree(tree)
the program just returns nil after execution. I've searched around the web to understand how argument passing works in lua (if it is by reference or by value) and found out that some types are passed by reference (like tables and functions) while others by value. Still, I made the global variable "tree" a table before passing it to the "createTree" function, and I even initialized "left" and "right" to be empty tables inside of "createTree" for the same purpose. What am I doing wrong?
It is probably necessary to initialize not by a new table, but only to set its values.
function createTree(tree, max)
if max > 0 then
tree.data = max
tree.left = {}
tree.right = {}
createTree(tree.left, max - 1)
createTree(tree.right, max - 1)
end
end
in Lua, arguments are passed by value. Assigning to an argument does not change the original variable.
Try this:
function createTree(max)
if max == 0 then
return nil
else
return {data = max, left = createTree(max-1), right = createTree(max-1)}
end
end
It is safe to think that for the most of the cases lua passes arguments by value. But for any object other than a number (numbers aren't objects actually), the "value" is actually a pointer to the said object.
When you do something like a={1,2,3} or b="asda" the values on the right are allocated somewhere dynamically, and a and b only get addresses of those. Thus, when you pass a to the function fun(a), the pointer is copied to a new variable inside function, but the a itself is unaffected:
function fun(p)
--p stores address of the same object, but `p` is not `a`
p[1]=3--by using the address you can
p[4]=1--alter the contents of the object
p[2]=nil--this will be seen outside
q={}
p={}--here you assign address of another object to the pointer
p=q--(here too)
end
Functions are also represented by pointers to them, you can use debug library to tinker with function object (change upvalues for example), this may affect how function executes, but, once again, you can not change where external references are pointing.
Strings are immutable objects, you can pass them around, there is a library that does stuff to them, but all the functions in that library return new string. So once, again external variable b from b="asda" would not be affected if you tried to do something with "asda" string inside the function.
I'm trying to improve performance by replacing a dynamic field (a transient getter with no underlying database representation) with a derived field so that I can use, e.g., Criteria to query my model. The original dynamic field was pretty simple:
Client resolveClient() {
if (prevCall && prevCall.client) {
return prevCall.client
} else {
return client
}
}
I don't know how to reproduce that with a single MySQL statement, so I figured I would go ahead and stick it into a stored function, defined as follows:
CREATE FUNCTION `request_client`(requestId long) RETURNS varchar(255) CHARSET utf8
begin
declare pci long;
declare clientId long;
declare clientName varchar(255);
select request.prev_call_id
from request
where request.id = requestId
into pci;
if pci is not null then
select call_history.client_id
from call_history
where call_history.call_id = pci
into clientId;
else
select request.client_id
from request
where request.id = requestId
into clientId;
end if;
select clients.client_name
from clients
where clients.client_id = clientId
into clientName;
return clientName;
end;
And then I call that function in a derived field:
String derivedFieldName
static mapping = {
derivedFieldName formula: '(select stored_function(id))'
}
The problem is that now when I run any query on the domain, even as simple as Request.list(), I get the following exception:
Class: java.io.StreamCorruptedException
Message: invalid stream header: 32303135
For extra fun, this is an abstract domain class. I don't know if that really makes any difference; it's still persisted to the database like any other domain, and I'm calling the query on the abstract class itself, not an implementation.
The most frustrating thing is that the derived field itself does work! I can successfully retrieve a client name using it; I just can't query the overall domain.
Finally, I am pretty confident that the derived property is the issue, as I have commented it out and can then successfully query the domain.
If anybody comes across this later, the problem actually was the abstract class. And not just that it's an abstract class -- it's an abstract domain class. Apparently, Grails doesn't support derived properties on those.
To move querying to the database I just had to start saving the resolved client into my Request domain :/
I would like to create a generic function. I'm novice in generic.
I've 3 private lists of different type. I want a public generic method for return 1 item of the list.
I've the code below. (I have it simplifie)
TFilter = class
private
FListFilter : TObjectList<TFilterEntity>;
FListFilterDate : TObjectList<TFilterDate>;
FListFilterRensParam : TObjectList<TFilterRensParam>;
public
function yGetFilter<T>(iIndice : integer) : T;
....
function TFilter .yGetFilter<T>(iIndice : integer) : T;
begin
if T = TFilterEntity then
result := T(FListFilter.Items[iIndice])
else
....
end;
I know that code doesn't run, but can you tell me if it's possible to do a thing that it ?
Just introduce a constraint of the generic parameter T. It has to be a class.
From the documentation:
A type parameter may be constrained by zero or one class type. As with interface type constraints, this declaration means that the compiler will require any concrete type passed as an argument to the constrained type param to be assignment compatible with the constraint class.
Compatibility of class types follows the normal rules of OOP type compatibilty - descendent types can be passed where their ancestor types are required.
Change declaration to:
function yGetFilter<T:class>(iIndice : integer) : T;
Update
It appears that in XE5 and earlier you get a compiler error:
E2015 Operator not applicable to this operand type
at this line:
if T = TFilterEntity then
In XE6 and above this bug is fixed.
To circumvent, do as David says in a comment:
if TClass(T) = TFilterEntity then
VHDL, using functions in for generate statement
I have a component that should be instantiated about 8000 times, I used for-generate statement with the help of some constant values for reducing amount of code, but I had to declare a function for parametrization of component connections.
My function looks like this:
function dim1_calc (
cmp_index : integer;
prt_index : integer
) return integer is
variable updw : integer := 0;
variable shft_v : integer := 0;
variable result : integer := 0;
begin
if (cmp_index < max_up) then
updw := 1;
else
updw := 2;
end if;
case prt_index is
when 1 =>
shft_v := cnst_rom(updw)(1) + (i-1);
when 2 =>
shft_v := cnst_rom(updw)(2) + (i);
--
--
--
when 32 =>
shft_v := cnst_rom(updw)(32) + (i);
when others =>
shft_v := 0;
end case;
if (updw = 1) then
if (shft_v = min_up & ((prt_index mod 2) = 0)) then
result <= max_up;
elsif (shft_v = max_up & ((prt_index mod 2) = 1)) then
result <= min_up;
elsif (shft_v < max_up) then
result <= shft_v;
else
result <= shft_v - max_up;
end if;
else
--something like first condition statements...
--
--
end if;
return result;
end function;
and part of my code that uses this function plus some related part looks like this:
--these type definitions are in my package
type nx_bits_at is array (natural range <>) of std_logic_vector (bits-1 downto 0);
type mxn_bits_at is array (natural range <>) of nx_bits_at;
--
--
--
component pn_cmpn is
port(
clk : in std_logic;
bn_to_pn : in nx_bits_at(1 to row_wght);
pn_to_bn : out nx_bits_at(1 to row_wght)
);
end component;
--
--
--
signal v2c : mxn_bits_at(1 to bn_num)(1 to col_wght);
signal c2v : mxn_bits_at(1 to pn_num)(1 to row_wght);
--
--
--
gen_pn : for i in (1 to pn_num) generate
ins_pn : pn_cmpn port map (
clk => clk,
bn_to_pn(1) => b2p (dim1_calc(i, 1)) (dim2_calc(i, 1)),
bn_to_pn(2) => b2p (dim1_calc(i, 2)) (dim2_calc(i, 2)),
.
.
.
bn_to_pn(32) => b2p (dim1_calc(i, 32)) (dim2_calc(i, 32)),
pn_to_bn => p2b (i)
);
end generate;
I know that using too many sequential statements together is not appropriate in general, and I'm avoiding them as much as possible, but in this case I assumed that this function won't synthesize into some real hardware, and synthesizer just calculates the output value and will put it in corresponding instantiations of that component. Am I right? or this way of coding leads to extra hardware compared to just 8000 instantiations.
PS1: Initially I used "0 to..." for defining ranges of the 2nd and 3rd dimension of my arrays, but because of confusion that were made in dimension calculation function based on for-generate statement parameter, I replaced them with "1 to...". Is that an OK! coding style or should I avoid it?
PS2: Is there a way that port mapping part in above code combines into something like this:
(I know this is strongly wrong, it's just a clarification of what I want)
gen_pn : for i in (1 to pn_num) generate
ins_pn : pn_cmpn port map (
clk => clk,
gen_bn_to_pn : for j in (1 to 32) generate
bn_to_pn(j) => b2p (dim1_calc(i, j)) (dim2_calc(i, j)),
end generate;
pn_to_bn => p2b (i)
);
end generate;
Let me give another example
Assume that I have a component instantiation like this:
ins_test : test_comp port map (
clk => clk,
test_port(1) => test_sig(2)
test_port(2) => test_sig(3)
test_port(3) => test_sig(4)
);
Is there a way that I can use for generate here? something like:
ins_test : test_comp port map (
clk => clk,
gen_pn : for i in (1 to 3) generate
test_port(i) => test_sig(i+1)
end generate;
);
PS3: Is it possible to call a function inside another function in VHDL?
Functions are usable this way. If you encounter problems, I am sure they will regard details in the design or design tools, rather than the basic approach.
One potential issue is that the function refers to some external "things" such as max_up, i, cnst_rom whose declarations are not part of the function nor parameters to it. This makes it an "impure function" which - because it refers to external state or even modifies it - has restrictions on calling it (because the external state may change, results may depend on order of evaluation etc).
If you can make it pure, do so. I have a feeling that max_up, cnst_rom are constants : if they aren't used elsewhere, declare them local to the function. And i probably ought to be a parameter.
If this is not possible, make the external declarations constants, and preferably wrap them and the function together in a package.
This will just generate the values you need in a small, comprehensible, maintainable form, and not an infinite volume of hardware. I have used a complex nest of functions performing floating point arithmetic then fiddly range reduction and integer rounding to initialise a lookup table, so fundamentally the approach does work.
Potential pitfall:
Some design tools have trouble with perfectly valid VHDL, if its use is slightly unorthodox. Synplicity cannot synthesise some forms of function (which DO generate hardware) though has no trouble with the equivalent procedure returning the result through an OUT parameter!. XST is considerably better.
XST parsing my lookup table init has an absurd slowdown, quadratic in the number of function calls. But only if you are using the old VHDL parser (the default for Spartan-3). Spartan-6 uses the new parser and works fine ( under a second instead of half an hour!) as do Modelsim and Isim. (haven't tried Synplicity on that project)
Some tools object to unorthodox things in port maps : you may get away with function calls there; or you may have to workaround tool bugs by initialising constants with the calls, and using those constants in the port maps.
And your supplementary questions:
PS1) The correct coding style for an array range is ... whatever makes your intent clear.
If you find yourself mentally offsetting by 1 and getting confused or even making errors, STOP! and improve the design.
Some good array indexing styles:
type colour is (red, green, blue);
subtype brightness is natural range 0 to 255;
hue : array (colour) of brightness;
gamma : array (brightness) of brightness;
-- here 0 is a legitimate value
channel : array (1 to 99) of frequency;
PS2) I think you're asking if you can nest generate statements. Yes.
Details may be awkward and difficult, but yes.
PS3) Yes of course! You can even declare functions local to others; eliminating the possibility they will be accidentally called somewhere they make no sense. They (impure functions) can access the execution scope of the outer function (or process), simplifying parameter lists.
Q1 - in this case I assumed that this function won't synthesize into some ...
It depends on which synthesizer you're using. See this relevant question and comments below.
Q2 - PS1: Initially I used "0 to..." for defining ranges of the ...
Surely it's OK. And please allow we to post a suggestion on coding style here. (from this book)
When defining the loop parameter specification, either use a type (or subtype) definition, or use predefined object attributes (e.g., PredefinedObject'range, PredefinedObject'length - 1 downto 0). Avoid using discrete range (e.g., 1 to 4).
This rule makes the code more reusable and flexible for maintenance.
Q3 - PS2: Is there a way that port mapping part in above code combines into ...
I think this is why you asked the 4th question. So refer to the next answer:).
Q4 - Is it possible to call a function inside another function in VHDL?
Though I can't find some official reference to this, the answer is yes.
PS: Coding rules are defined by the synthesizer tools. So the best way to find an answer is to try it yourself.