In Lua, using the = operator without an l-value seems to be equivalent to a print(r-value), here are a few examples run in the Lua standalone interpreter:
> = a
nil
> a = 8
> = a
8
> = 'hello'
hello
> = print
function: 003657C8
And so on...
My question is : where can I find a detailed description of this use for the = operator? How does it work? Is it by implying a special default l-value? I guess the root of my problem is that I have no clue what to type in Google to find info about it :-)
edit:
Thanks for the answers, you are right it's a feature of the interpreter. Silly question, for I don't know which reason I completely overlooked the obvious. I should avoid posting before the morning coffee :-) For completeness, here is the code dealing with this in the interpreter:
while ((status = loadline(L)) != -1) {
if (status == 0) status = docall(L, 0, 0);
report(L, status);
if (status == 0 && lua_gettop(L) > 0) { /* any result to print? */
lua_getglobal(L, "print");
lua_insert(L, 1);
if (lua_pcall(L, lua_gettop(L)-1, 0, 0) != 0)
l_message(progname, lua_pushfstring(L,
"error calling " LUA_QL("print") " (%s)",
lua_tostring(L, -1)));
}
}
edit2:
To be really complete, the whole trick about pushing values on the stack is in the "pushline" function:
if (firstline && b[0] == '=') /* first line starts with `=' ? */
lua_pushfstring(L, "return %s", b+1); /* change it to `return' */
Quoting the man page:
In interactive mode ... If a line starts with '=', then lua displays the values of all the expressions in the remainder of the line. The expressions must be separated by commas.
I think that must be a feature of the stand alone interpreter. I can't make that work on anything I have compiled lua into.
I wouldn't call it a feature - the interpreter just returns the result of the statement. It's his job, isn't it?
Assignment isn't an expression that returns something in Lua like it is in C.
Related
bool runOnFunction(Function &F) override {
outs() << "Inside Function: "<<F.getName()<<"\n";
int i = 0;
map<int, Instruction*> work;
for(BasicBlock &BB : F)
for(Instruction &I : BB){
if(i == 15)
work.insert({i, &I});
i++;
}
std::map<int, Instruction*>::iterator it = work.begin();
it->second->eraseFromParent();
return true;
}
The above is my code snippet. Here, in the above code, I would like to remove an instruction randomly.. just for the sake of knowing how to use this api. But, It is ending up with segmentation fault!!, no matter what I try. Need some guidance, here please
Inside Function: change_g
While deleting: i32 %
Use still stuck around after Def is destroyed: %add = add nsw i32 <badref>, %l
opt: /home/user/llvm-project/llvm/lib/IR/Value.cpp:103: llvm::Value::~Value(): Assertion `materialized_use_empty() && "Uses remain when a value is destroyed!"' failed.
First of all, it's not a segmentation fault but an assertion which tells you that something went wrong. In particular the message explains that you can not erase an instruction until any of its uses is still present in function.
Usually you'd first create a new instruction, replace all uses of to-be-removed instruction with new result (via Value::replaceAllUsesWith()) and only then erase.
I need a specific format for a float number: (sign)xx.dd
when trying to set a string.format for thiss format I get odd results.
h= 5.127 --(it should beconverted to +05.13)
print(string.format("%+05.2f",h))
--> 05.13
print(string.format("%+06.2f",h))
--> 005.13
h= -5.127 --(it should beconverted to -05.13)
print(string.format("%05.2f",h))
--> -5.13
print(string.format("%06.2f",h))
--> 0-5.13
Of course, I have an easy workaround, but I think that there is something wrong in this build.
build created on 2018-04-09 15:12
powered by Lua 5.1.4 on SDK 2.2.1(cfd48f3)
BR,
eHc
This is a bug (or undocumented deficiency) in NodeMCU.
Lua implements most of the handling of string.format format specifiers by handing them off to the C standard library's sprintf function. (There are a few things sprintf allows that Lua doesn't, but + ought to work fine.)
NodeMCU has modified Lua to replace most (or all) of the standard library calls with calls to replacement functions defined by NodeMCU (which is normally crazy, but maybe okay in the embedded systems domain). NodeMCU's sprintf implementation doesn't support +.
This is the relevant code from NodeMCU's source (c_stdio.c). Notice that unknown characters in the format specifier are silently ignored:
for (; *s; s++) {
if (strchr("bcdefgilopPrRsuxX%", *s))
break;
else if (*s == '-')
fmt = FMT_LJUST;
else if (*s == '0')
fmt = FMT_RJUST0;
else if (*s == '~')
fmt = FMT_CENTER;
else if (*s == '*') {
// [snip]
// ...
} else if (*s >= '1' && *s <= '9') {
// [snip]
// ...
} else if (*s == '.')
haddot = 1;
}
Similarly, the 0 formatting is not implemented currently for numbers -- as you have noticed, it just pads on the left regardless of sign.
I've been trying to implement a BASIC language interpreter (in C/C++) but I haven't found any book or (thorough) article which explains the process of parsing the language constructs. Some commands are rather complex and hard to parse, especially conditionals and loops, such as IF-THEN-ELSE and FOR-STEP-NEXT, because they can mix variables with constants and entire expressions and code and everything else, for example:
10 IF X = Y + Z THEN GOTO 20 ELSE GOSUB P
20 FOR A = 10 TO B STEP -C : PRINT C$ : PRINT WHATEVER
30 NEXT A
It seems like a nightmare to be able to parse something like that and make it work. And to make things worse, programs written in BASIC can easily be a tangled mess. That's why I need some advice, read some book or whatever to make my mind clear about this subject. What can you suggest?
You've picked a great project - writing interpreters can be lots of fun!
But first, what do we even mean by an interpreter? There are different types of interpreters.
There is the pure interpreter, where you simply interpret each language element as you find it. These are the easiest to write, and the slowest.
A step up, would be to convert each language element into some sort of internal form, and then interpret that. Still pretty easy to write.
The next step, would be to actually parse the language, and generate a syntax tree, and then interpret that. This is somewhat harder to write, but once you've done it a few times, it becomes pretty easy.
Once you have a syntax tree, you can fairly easily generate code for a custom stack virtual machine. A much harder project is to generate code for an existing virtual machine, such as the JVM or CLR.
In programming, like most engineering endeavors, careful planning greatly helps, especially with complicated projects.
So the first step is to decide which type of interpreter you wish to write. If you have not read any of a number of compiler books (e.g., I always recommend Niklaus Wirth's "Compiler Construction" as one of the best introductions to the subject, and is now freely available on the web in PDF form), I would recommend that you go with the pure interpreter.
But you still need to do some additional planning. You need to rigorously define what it is you are going to be interpreting. EBNF is great for this. For a gentile introduction EBNF, read the first three parts of a Simple Compiler at http://www.semware.com/html/compiler.html It is written at the high school level, and should be easy to digest. Yes, I tried it on my kids first :-)
Once you have defined what it is you want to be interpreting, you are ready to write your interpreter.
Abstractly, you're simple interpreter will be divided into a scanner (technically, a lexical analyzer), a parser, and an evaluator. In the simple pure interpolator case, the parser and evaluator will be combined.
Scanners are easy to write, and easy to test, so we won't spend any time on them. See the aforementioned link for info on crafting a simple scanner.
Lets (for example) define your goto statement:
gotostmt -> 'goto' integer
integer -> [0-9]+
This tells us that when we see the token 'goto' (as delivered by the scanner), the only thing that can follow is an integer. And an integer is simply a string a digits.
In pseudo code, we might handle this as so:
(token - is the current token, which is the current element just returned via the scanner)
loop
if token == "goto"
goto_stmt()
elseif token == "gosub"
gosub_stmt()
elseif token == .....
endloop
proc goto_stmt()
expect("goto") -- redundant, but used to skip over goto
if is_numeric(token)
--now, somehow set the instruction pointer at the requested line
else
error("expecting a line number, found '%s'\n", token)
end
end
proc expect(s)
if s == token
getsym()
return true
end
error("Expecting '%s', found: '%s'\n", curr_token, s)
end
See how simple it is? Really, the only hard thing to figure out in a simple interpreter is the handling of expressions. A good recipe for handling those is at: http://www.engr.mun.ca/~theo/Misc/exp_parsing.htm Combined with the aforementioned references, you should have enough to handle the sort of expressions you would encounter in BASIC.
Ok, time for a concrete example. This is from a larger 'pure interpreter', that handles a enhanced version of Tiny BASIC (but big enough to run Tiny Star Trek :-) )
/*------------------------------------------------------------------------
Simple example, pure interpreter, only supports 'goto'
------------------------------------------------------------------------*/
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <setjmp.h>
#include <ctype.h>
enum {False=0, True=1, Max_Lines=300, Max_Len=130};
char *text[Max_Lines+1]; /* array of program lines */
int textp; /* used by scanner - ptr in current line */
char tok[Max_Len+1]; /* the current token */
int cur_line; /* the current line number */
int ch; /* current character */
int num; /* populated if token is an integer */
jmp_buf restart;
int error(const char *fmt, ...) {
va_list ap;
char buf[200];
va_start(ap, fmt);
vsprintf(buf, fmt, ap);
va_end(ap);
printf("%s\n", buf);
longjmp(restart, 1);
return 0;
}
int is_eol(void) {
return ch == '\0' || ch == '\n';
}
void get_ch(void) {
ch = text[cur_line][textp];
if (!is_eol())
textp++;
}
void getsym(void) {
char *cp = tok;
while (ch <= ' ') {
if (is_eol()) {
*cp = '\0';
return;
}
get_ch();
}
if (isalpha(ch)) {
for (; !is_eol() && isalpha(ch); get_ch()) {
*cp++ = (char)ch;
}
*cp = '\0';
} else if (isdigit(ch)) {
for (; !is_eol() && isdigit(ch); get_ch()) {
*cp++ = (char)ch;
}
*cp = '\0';
num = atoi(tok);
} else
error("What? '%c'", ch);
}
void init_getsym(const int n) {
cur_line = n;
textp = 0;
ch = ' ';
getsym();
}
void skip_to_eol(void) {
tok[0] = '\0';
while (!is_eol())
get_ch();
}
int accept(const char s[]) {
if (strcmp(tok, s) == 0) {
getsym();
return True;
}
return False;
}
int expect(const char s[]) {
return accept(s) ? True : error("Expecting '%s', found: %s", s, tok);
}
int valid_line_num(void) {
if (num > 0 && num <= Max_Lines)
return True;
return error("Line number must be between 1 and %d", Max_Lines);
}
void goto_line(void) {
if (valid_line_num())
init_getsym(num);
}
void goto_stmt(void) {
if (isdigit(tok[0]))
goto_line();
else
error("Expecting line number, found: '%s'", tok);
}
void do_cmd(void) {
for (;;) {
while (tok[0] == '\0') {
if (cur_line == 0 || cur_line >= Max_Lines)
return;
init_getsym(cur_line + 1);
}
if (accept("bye")) {
printf("That's all folks!\n");
exit(0);
} else if (accept("run")) {
init_getsym(1);
} else if (accept("goto")) {
goto_stmt();
} else {
error("Unknown token '%s' at line %d", tok, cur_line); return;
}
}
}
int main() {
int i;
for (i = 0; i <= Max_Lines; i++) {
text[i] = calloc(sizeof(char), (Max_Len + 1));
}
setjmp(restart);
for (;;) {
printf("> ");
while (fgets(text[0], Max_Len, stdin) == NULL)
;
if (text[0][0] != '\0') {
init_getsym(0);
if (isdigit(tok[0])) {
if (valid_line_num())
strcpy(text[num], &text[0][textp]);
} else
do_cmd();
}
}
}
Hopefully, that will be enough to get you started. Have fun!
I will certainly get beaten by telling this ...but...:
First, I am actually working on a standalone library ( as a hobby ) that is made of:
a tokenizer, building linear (flat list) of tokens from the source text and following the same sequence as the text ( lexems created from the text flow ).
A parser by hands (syntax analyse; pseudo-compiler )
There is no "pseudo-code" nor "virtual CPU/machine".
Instructions(such as 'return', 'if' 'for' 'while'... then arithemtic expressions ) are represented by a base c++-struct/class and is the object itself. The base object, I name it atom, have a virtual method called "eval", among other common members, that is the "execution/branch" also by itself. So no matter I have an 'if' statement with its possible branchings ( single statement or bloc of statements/instructions ) as true or false condition, it will be called from the base virtual atom::eval() ... and so on for everything that is an atom.
Even 'objects' such as variables are 'atom'. 'eval()' will simply return its value from a variant container held by the atom itself ( pointer, refering to the 'local' variant instance (the instance variant iself) held the 'atom' or to another variant held by an atom that is created in a given 'bloc/stack'. So 'atom' are 'inplace' instructions/objects.
As of now, as an example, chunk of not really meaningful 'code' as below just works:
r = 5!; // 5! : (factorial of 5 )
Response = 1 + 4 - 6 * --r * ((3+5)*(3-4) * 78);
if (Response != 1){ /* '<>' also is not equal op. */
return r^3;
}
else{
return 0;
}
Expressions ( arithemtics ) are built into binary tree expression:
A = b+c; =>
=
/ \
A +
/ \
b c
So the 'instruction'/statement for expression like above is the tree-entry atom that in the above case, is the '=' (binary) operator.
The tree is built with atom::r0,r1,r2 :
atom 'A' :
r0
|
A
/ \
r1 r2
Regarding 'full-duplex' mecanism between c++ runtime and the 'script' library, I've made class_adaptor and adaptor<> :
ex.:
template<typename R, typename ...Args> adaptor_t<T,R, Args...>& import_method(const lstring& mname, R (T::*prop)(Args...)) { ... }
template<typename R, typename ...Args> adaptor_t<T,R, Args...>& import_property(const lstring& mname, R (T::*prop)(Args...)) { ... }
Second: I know there are plenty of tools and libs out there such as lua, boost::bind<*>, QML, JSON, etc... But in my situation, I need to create my very own [edit] 'independant' [/edit] lib for "live scripting". I was scared that my 'interpreter' could take a huge amount of RAM, but I am surprised that it is not as big as using QML,jscript or even lua :-)
Thank you :-)
Don't bother with hacking a parser together by hand. Use a parser generator. lex + yacc is the classic lexer/parser generator combination, but a Google search will reveal plenty of others.
I have some trouble compiling lodepng (http://lodev.org/lodepng/) for D into my project.
In Encode.d I have the following code, where the compiler does not expect the assert statements.
Removing this block solves the issue.
invariant
{
assert(compressionLevel >=0 && compressionLevel <= 9, "invalid zlib compression level");
assert(targetColorType == ColorType.Any ||
targetColorType == ColorType.RGB ||
targetColorType == ColorType.RGBA, "colortype is not supported");
}
In Decode.d I have even more trouble, with the error "no identifier for declarator inout(value)"
for the middle line in:
info.backgroundColor.length = chunk.data.length / 2;
foreach(index, inout value; info.backgroundColor)
value = chunk.data[index * 2];
Is there some trouble with old syntax here, and how do I fix it?
Is there some other way to create png images in D in a simple manner?
Not sure about the invariant problem, but the second problem should be solved by replacing the "inout" with "ref" (D2 syntax change).
I gave up on lodepng, and used the code on
http://www.dsource.org/projects/plot2kill/browser/trunk/png.d
which works after some minor changes.
using grep, vim's grep, or another unix shell command, I'd like to find the functions in a large cpp file that contain a specific word in their body.
In the files that I'm working with the word I'm looking for is on an indented line, the corresponding function header is the first line above the indented line that starts at position 0 and is not a '{'.
For example searching for JOHN_DOE in the following code snippet
int foo ( int arg1 )
{
/// code
}
void bar ( std::string arg2 )
{
/// code
aFunctionCall( JOHN_DOE );
/// more code
}
should give me
void bar ( std::string arg2 )
The algorithm that I hope to catch in grep/vim/unix shell scripts would probably best use the indentation and formatting assumptions, rather than attempting to parse C/C++.
Thanks for your suggestions.
I'll probably get voted down for this!
I am an avid (G)VIM user but when I want to review or understand some code I use Source Insight. I almost never use it as an actual editor though.
It does exactly what you want in this case, e.g. show all the functions/methods that use some highlighted data type/define/constant/etc... in a relations window...
(source: sourceinsight.com)
Ouch! There goes my rep.
As far as I know, this can't be done. Here's why:
First, you have to search across lines. No problem, in vim adding a _ to a character class tells it to include new lines. so {_.*} would match everything between those brackets across multiple lines.
So now you need to match whatever the pattern is for a function header(brittle even if you get it to work), then , and here's the problem, whatever lines are between it and your search string, and finally match your search string. So you might have a regex like
/^\(void \+\a\+ *(.*)\)\_.*JOHN_DOE
But what happens is the first time vim finds a function header, it starts matching. It then matches every character until it finds JOHN_DOE. Which includes all the function headers in the file.
So the problem is that, as far as I know, there's no way to tell vim to match every character except for this regex pattern. And even if there was, a regex is not the tool for this job. It's like opening a beer with a hammer. What we should do is write a simple script that gives you this info, and I have.
fun! FindMyFunction(searchPattern, funcPattern)
call search(a:searchPattern)
let lineNumber = line(".")
let lineNumber = lineNumber - 1
"call setpos(".", [0, lineNumber, 0, 0])
let lineString = getline(lineNumber)
while lineString !~ a:funcPattern
let lineNumber = lineNumber - 1
if lineNumber < 0
echo "Function not found :/"
endif
let lineString = getline(lineNumber)
endwhile
echo lineString
endfunction
That should give you the result you want and it's way easier to share, debug, and repurpose than a regular expression spit from the mouth of Cthulhu himself.
Tough call, although as a starting point I would suggest this wonderful VIM Regex Tutorial.
You cannot do that reliably with a regular expression, because code is not a regular language. You need a real parser for the language in question.
Arggh! I admit this is a bit over the top:
A little program to filter stdin, strip comments, and put function bodies on the same line. It'll get fooled by namespaces and function definitions inside class declarations, besides other things. But it might be a good start:
#include <stdio.h>
#include <assert.h>
int main() {
enum {
NORMAL,
LINE_COMMENT,
MULTI_COMMENT,
IN_STRING,
} state = NORMAL;
unsigned depth = 0;
for(char c=getchar(),prev=0; !feof(stdin); prev=c,c=getchar()) {
switch(state) {
case NORMAL:
if('/'==c && '/'==prev)
state = LINE_COMMENT;
else if('*'==c && '/'==prev)
state = MULTI_COMMENT;
else if('#'==c)
state = LINE_COMMENT;
else if('\"'==c) {
state = IN_STRING;
putchar(c);
} else {
if(('}'==c && !--depth) || (';'==c && !depth)) {
putchar(c);
putchar('\n');
} else {
if('{'==c)
depth++;
else if('/'==prev && NORMAL==state)
putchar(prev);
else if('\t'==c)
c = ' ';
if(' '==c && ' '!=prev)
putchar(c);
else if(' '<c && '/'!=c)
putchar(c);
}
}
break;
case LINE_COMMENT:
if(' '>c)
state = NORMAL;
break;
case MULTI_COMMENT:
if('/'==c && '*'==prev) {
c = '\0';
state = NORMAL;
}
break;
case IN_STRING:
if('\"'==c && '\\'!=prev)
state = NORMAL;
putchar(c);
break;
default:
assert(!"bug");
}
}
putchar('\n');
return 0;
}
Its c++, so just it in a file, compile it to a file named 'stripper', and then:
cat my_source.cpp | ./stripper | grep JOHN_DOE
So consider the input:
int foo ( int arg1 )
{
/// code
}
void bar ( std::string arg2 )
{
/// code
aFunctionCall( JOHN_DOE );
/// more code
}
The output of "cat example.cpp | ./stripper" is:
int foo ( int arg1 ) { }
void bar ( std::string arg2 ){ aFunctionCall( JOHN_DOE ); }
The output of "cat example.cpp | ./stripper | grep JOHN_DOE" is:
void bar ( std::string arg2 ){ aFunctionCall( JOHN_DOE ); }
The job of finding the function name (guess its the last identifier to precede a "(") is left as an exercise to the reader.
For that kind of stuff, although it comes to primitive searching again, I would recommend compview plugin. It will open up a search window, so you can see the entire line where the search occured and automatically jump to it. Gives a nice overview.
(source: axisym3.net)
Like Robert said Regex will help. In command mode start a regex search by typing the "/" character followed by your regex.
Ctags1 may also be of use to you. It can generate a tag file for a project. This tag file allows a user to jump directly from a function call to it's definition even if it's in another file using "CTRL+]".
u can use grep -r -n -H JOHN_DOE * it will look for "JOHN_DOE" in the files recursively starting from the current directory
you can use the following code to practically find the function which contains the text expression:
public void findFunction(File file, String expression) {
Reader r = null;
try {
r = new FileReader(file);
} catch (FileNotFoundException ex) {
ex.printStackTrace();
}
BufferedReader br = new BufferedReader(r);
String match = "";
String lineWithNameOfFunction = "";
Boolean matchFound = false;
try {
while(br.read() > 0) {
match = br.readLine();
if((match.endsWith(") {")) ||
(match.endsWith("){")) ||
(match.endsWith("()")) ||
(match.endsWith(")")) ||
(match.endsWith("( )"))) {
// this here is because i guessed that method will start
// at the 0
if((match.charAt(0)!=' ') && !(match.startsWith("\t"))) {
lineWithNameOfFunction = match;
}
}
if(match.contains(expression)) {
matchFound = true;
break;
}
}
if(matchFound)
System.out.println(lineWithNameOfFunction);
else
System.out.println("No matching function found");
} catch (IOException ex) {
ex.printStackTrace();
}
}
i wrote this in JAVA, tested it and works like a charm. has few drawbacks though, but for starters it's fine. didn't add support for multiple functions containing same expression and maybe some other things. try it.