Execute Brain****/Ada
This is a simple implementation of Brainf*** (it will be called just BF in what follows). It is written in Ada.
Standalone interpreter
This implementation imposes hard limits in the size of both the memory and the program size. The whole program is read first, and then interpreted. The program must be stored in a file. The filename is given as the only argument to the interpreter.
The program reads input data from the standard input and writes output data to the standard output. Error messages go to the standard error output. Of course, these channels can be redirected to files, as usual, when invoking the BF interpreter.
The program is stored internally in a fixed length array of characters. Programs larger than the array size cannot be processed.
The internal data memory is implemented as a fixed length array of integers. Programs that attempt to go beyond the memory limits will stop with an error message at run time.
To allow using the interpreter in an interactive terminal session, control characters are ignored on input. But they can be generated on output, like any other ASCII character.
Memory cells are intended to have non-negative values. A special negative value represents an undefined value. End-of-file conditions are signaled by this special undefined value in read/write operations.
More detailed information about the code can be found in the comments throughout it.
<lang ada>-- BF Interpreter
-- Usage: bf programfile[.bf]
-- reads input data from standard input (control chars are ignored) -- writes output data to standard output -- writes error messages to standard error
with Ada.Text_Io; use Ada.Text_Io; with Ada.Command_Line; use Ada.Command_Line;
procedure Bf is
-- Data structures for memory Bottom : constant Integer := - 1; subtype T_Data is Integer range Bottom..Integer'Last; -- value range Mem_Last : constant Integer := 30000; -- memory size M : array (0 .. Mem_Last) of T_Data := (others => 0); -- memory cells Mp : Integer; -- memory pointer
-- Data structures for program text Prog_Name : String := Argument (1); -- program file name Prog_Suffix : constant String := ".bf"; -- standard program filename extension Program : File_Type; -- program file Prog_Last : constant Integer := 30000; -- program storage size P : array (0 .. Prog_Last) of Character; -- program Pp : Integer; -- program pointer Prog_Len : Integer; -- program length
-- Data structures for program execution control Level : Integer; -- nested loops level Data : Character; -- input datum Ok : Boolean; -- program execution switch End_Input : Boolean := False; -- input EOF condition End_Output : Boolean := False; -- output EOF condition
-- Compose and print an error message
procedure Msgerr (
Msg : in String ) is
begin
New_Line;
Put_Line( Standard_Error, "** error: " & Msg );
Ok := False;
end;
begin
--get and open the program file
declare
begin
Open( Program, In_File, Prog_Name);
exception
when others =>
Open( Program, In_File, Prog_Name & Prog_Suffix);
end;
-- first, read the whole program file
Prog_Len := 0;
while not End_Of_File( Program ) loop
Get_Immediate(Program, P(Prog_Len));
Prog_Len := Prog_Len+1;
end loop;
Close( Program );
-- then, interpret the program
Pp := 0;
Mp := 0;
Ok := True;
End_Input := False;
End_Output := False;
while Ok and (Pp < Prog_Len) loop -- while interpreting
case P(Pp) is
when '+' => -- (+) increment memory location
M(Mp) := M(Mp)+1;
when '-' => -- (-) decrement memory location
if M(Mp) <= Bottom then
Msgerr( "arithmetic underflow" );
else
M(Mp) := M(Mp)-1;
end if;
when '.' => -- (.) output data (print char)
if End_Output then
Msgerr("attempt to write past EOF");
elsif M(Mp) < 0 then
End_Output := True;
else
Put( Character'Val(M(Mp)) );
end if;
when ',' => -- (,) input data (read char)
if End_Input then
Msgerr("attempt to read past EOF");
else
loop
if End_Of_File(Standard_Input) then
M(Mp) := Bottom;
End_Input := True;
exit;
else
Get( Data );
M(Mp) := Character'Pos(Data);
-- ignore control chars
exit when Data >= ' ';
end if;
end loop;
end if;
when '>' => -- (>) increment memory pointer (use next cell)
Mp := Mp+1;
if Mp >= Mem_Last then
Msgerr("memory pointer overflow");
end if;
when '<' => -- (<) decrement memory pointer (use previous cell)
Mp := Mp - 1;
if Mp < 0 then
Msgerr("memory pointer underflow");
end if;
when '[' => -- ([) begin of loop structure
if M(Mp) = 0 then
-- terminate loop, goto matching ']'
Pp := Pp+1;
Level := 0;
while Pp < Prog_Len and then (Level > 0 or else P(Pp) /= ']') loop
if P(Pp) = '[' then
Level := Level+1;
end if;
if P(Pp) = ']' then
Level := Level-1;
end if;
Pp := Pp+1;
end loop;
if Pp >= Prog_Len then
Msgerr("no matching ']'");
end if;
end if;
when ']' => -- (]) end of loop structure
if M(Mp) /= 0 then
-- repeat loop, goto matching '['
Pp := Pp-1;
Level := 0;
while Pp >= 0 and then (Level > 0 or else P(Pp) /= '[') loop
if P(Pp) = ']' then
Level := Level+1;
end if;
if P(Pp) = '[' then
Level := Level-1;
end if;
Pp := Pp-1;
end loop;
if Pp < 0 then
Msgerr("no matching '['");
end if;
end if;
when others =>
null; -- (?) ignore unrecognized command
end case;
Pp := Pp+1;
end loop; -- while interpreting
New_Line;
end Bf;</lang>
Callable interpreter
This implementation provides a procedure that can be called to interpret a Brainf*** stored in a string. The memory is passed as a parameter. Input and output of the memory cells is stream. By default the input and output streams are used. The interpreter uses the native machine memory. Upon errors such as addressing errors and program errors (unclosed brackets) Constraint_Error is propagated. <lang Ada> with Ada.Streams; use Ada.Streams; with Ada.Text_IO.Text_Streams; use Ada.Text_IO.Text_Streams; with Ada.Text_IO; use Ada.Text_IO; with System.Storage_Elements; use System.Storage_Elements;
procedure BF
( Source : String;
Memory : in out Storage_Array;
Input : access Root_Stream_Type'Class := Stream (Standard_Input);
Output : access Root_Stream_Type'Class := Stream (Standard_Output)
) is
subtype Address is Storage_Offset range Memory'Range;
PC : Address := Address'First;
Index : Integer := Source'First;
Nesting : Natural := 0;
begin
while Index <= Source'Last loop
case Source (Index) is
when '>' => -- Increment PC
PC := PC + 1;
when '<' => -- Decrement PC
PC := PC - 1;
when '+' => -- Increment at PC
Memory (PC) := Memory (PC) + 1;
when '-' => -- Decrement at PC
Memory (PC) := Memory (PC) - 1;
when '.' => -- Output at PC
Storage_Element'Write (Output, Memory (PC));
when ',' => -- Input at PC
Storage_Element'Read (Input, Memory (PC));
when '[' => -- Forward if zero at PC
if Memory (PC) = 0 then
loop
Index := Index + 1;
case Source (Index) is
when '[' =>
Nesting := Nesting + 1;
when ']' =>
exit when Nesting = 0;
Nesting := Nesting - 1;
when others =>
null;
end case;
end loop;
end if;
when ']' => -- Backward if non-zero at PC
if Memory (PC) /= 0 then
loop
Index := Index - 1;
case Source (Index) is
when '[' =>
exit when Nesting = 0;
Nesting := Nesting - 1;
when ']' =>
Nesting := Nesting + 1;
when others =>
null;
end case;
end loop;
end if;
when others => -- Comment
null;
end case;
Index := Index + 1;
end loop;
end BF; </lang>
Test programs
Hello world
<lang Ada> with System.Storage_Elements; use System.Storage_Elements; with BF;
procedure Test_BF_Hello is
Memory : Storage_Array := (0..100_000 => 0);
begin
BF ("++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.", Memory);
end Test_BF_Hello; </lang> Sample output:
Hello World!
Bracket test
<lang Ada> with System.Storage_Elements; use System.Storage_Elements; with BF;
procedure Test_BF is
Memory : Storage_Array := (0..100_000 => 0);
begin
BF (">>++++[<++++[<++++>-]>-]<<.[-]++++++++++.", Memory);
end Test_BF; </lang> Sample output:
@