26 KiB
Nasal - Modern Interpreter
Contents
- Introduction
- Compile
- Usage
- Tutorial
- Release Notes
- Development History
- Benchmark
- Difference
- Trace Back Info
- Debugger
- REPL
Contact us if having great ideas to share!
- E-mail: lhk101lhk101@qq.com
Introduction
Nasal is an ECMAscript-like language used in FlightGear. The designer is Andy Ross.
This interpreter is totally rewritten by ValKmjolnir using C++(-std=c++17)
without reusing the code in Andy Ross's nasal interpreter.
But we really appreciate that Andy created this amazing programming language.
This project uses MIT license (2019/7 ~ 2021/5/4 ~ 2023/5), GPL v2 license (since 2023/6).
Why writing this nasal interpreter?
2019 summer, members in FGPRC told me that it is hard to debug with nasal-console in Flightgear, especially when checking syntax errors. So i wrote a new interpreter to help checking syntax error and runtime error.
I wrote the lexer, parser and bytecode virtual machine to help checking errors. We found it much easier to debug.
You could also use this language to write some interesting programs and run them without the lib of Flightgear. You could add your own modules to make the interpreter a useful tool in your own projects.
How to Compile
Better download the latest update source of the interpreter and build it! It's quite easy to build this interpreter, what you need are only two things: C++ compiler and the make. There is no third-party library used in this project.
CAUTION: If want to use the release zip/tar.gz file to build the interpreter, please read the Release Notes to make sure this release file has no fatal bugs.
Windows (MinGW-w64)
Make sure your MinGW thread model is posix thread model, otherwise it may not have the thread library.
mkdir build
mingw32-make nasal.exe -j4
Windows (Visual Studio)
This project gives a CMakelists.txt for you to create project in Visual Studio.
Linux/macOS/Unix
mkdir build
make -j4
You could choose which compiler you want to use:
make nasal CXX=...
How to Use
If your system is Windows and you want to output unicode, you could write this in nasal code:
if(os.platform()=="windows")
system("chcp 65001");
Tutorial
Nasal is really easy to learn. Reading this tutorial will not takes you over 15 minutes. If you have learnt C/C++/Javascript before, this will take less time. You could totally use it after reading this simple tutorial:
Basic type
none is error type used to interrupt the execution.
This type is not created by user program.
nil is a null type. Just like null.
var spc=nil;
num has 3 formats: dec, hex and oct. Using IEEE754 double to store.
# this language use '#' to write notes
var n=2.71828; # dec
var n=2.147e16; # dec
var n=1e-10; # dec
var n=0xAA55; # hex
var n=0o170001; # oct
# caution: true and false also useful in nasal now
var n=true; # in fact n is now 1.0
var n=false; # in face n is now 0.0
str has 3 formats. The third one is used to declare a character.
var s='str';
var s="another string";
var s=`c`;
# some special characters is allowed in this language:
'\a'; '\b'; '\e'; '\f';
'\n'; '\r'; '\t'; '\v';
'\0'; '\\'; '\?'; '\'';
'\"';
vec has unlimited length and can store all types of values.
var vec=[];
var vec=[0,nil,{},[],func(){return 0}];
append(vec,0,1,2);
hash is a hashmap (or like a dict in python) that stores values with strings/identifiers as the key.
var hash={
member1:nil,
member2:"str",
"member3":"member\'s name can also be a string constant",
funct:func(){
return me.member2~me.member3;
}
};
func is a function type (in fact it is lambda).
var f=func(x,y,z){
return nil;
}
# function could be declared without parameters and `(`, `)`
var f=func{
return 114514;
}
var f=func(x,y,z,deft=1){
return x+y+z+deft;
}
var f=func(args...){
var sum=0;
foreach(var i;args)
sum+=i;
return sum;
}
upval is used to store upvalues, used in vm to make sure closure runs correctly.
obj is used to store other complex C/C++ data types.
This type is created by native-function of nasal. If want to define a new data type, see how to add native-functions by editing code.
Operators
Nasal has basic math operators + - * / and a special operator ~ that joints strings.
1+2-(1+3)*(2+4)/(16-9);
"str1"~"str2";
For conditional expressions, operators == != < > <= >= are used to compare two values.
and or have the same function as C/C++ && ||.
1+1 and (1<0 or 1>0);
1<=0 and 1>=0;
1==0 or 1!=0;
Unary operators - ! have the same function as C/C++.
-1;
!0;
Bitwise operators ~ | & ^ have the same function as C/C++.
# these operators will:
# 1. convert f64 to i32 (static_cast<int32_t>)
# 2. do the bitwise function
~0x80000000; # not 2147483647
0x8|0x1; # or
0x1&0x2; # and
0x8^0x1; # xor
Operators = += -= *= /= ~= ^= &= |= are used in assignment expressions.
a=b=c=d=1;
a+=1;
a-=1;
a*=1;
a/=1;
a~="string";
a^=0xff;
a&=0xca;
a|=0xba;
Definition
As follows.
var a=1; # define single variable
var (a,b,c)=[0,1,2]; # define multiple variables from a vector
var (a,b,c)=(0,1,2); # define multiple variables from a tuple
Multi-assignment
The last one is often used to swap two variables.
(a,b[0],c.d)=[0,1,2];
(a,b[1],c.e)=(0,1,2);
(a,b)=(b,a);
Conditional expression
In nasal there's a new key word elsif.
It has the same functions as else if.
if(1){
;
}elsif(2){
;
}else if(3){
;
}else{
;
}
Loop
While loop and for loop is simalar to C/C++.
while(condition)
continue;
for(var i=0;i<10;i+=1)
break;
Nasal has another two kinds of loops that iterates through a vector:
forindex will get the index of a vector. Index will be 0 to size(elem)-1.
forindex(var i;elem)
print(elem[i]);
foreach will get the element of a vector. Element will be elem[0] to elem[size(elem)-1].
foreach(var i;elem)
print(i);
Subvec
Nasal provides this special syntax to help user generate a new vector by getting values by one index or getting values by indexes in a range from an old vector.
If there's only one index in the bracket, then we will get the value directly.
Use index to search one element in the string will get the ascii number of this character.
If you want to get the character, use built-in function chr().
a[0];
a[-1,1,0:2,0:,:3,:,nil:8,3:nil,nil:nil];
"hello world"[0];
Special function call
This is not very efficient, because hashmap use string as the key to compare.
But if it really useful, the efficientcy may not be so important...
f(x:0,y:nil,z:[]);
Lambda
Also functions have this kind of use:
func(x,y){
return x+y
}(0,1);
func(x){
return 1/(1+math.exp(-x));
}(0.5);
There's an interesting test file y-combinator.nas,
try it for fun:
var fib=func(f){
return f(f);
}(
func(f){
return func(x){
if(x<2) return x;
return f(f)(x-1)+f(f)(x-2);
}
}
);
Closure
Closure means you could get the variable that is not in the local scope of a function that you called.
Here is an example, result is 1:
var f=func(){
var a=1;
return func(){return a;};
}
print(f()());
Using closure makes it easier to OOP.
var student=func(n,a){
var (name,age)=(n,a);
return {
print_info:func() {println(name,' ',age);},
set_age: func(a){age=a;},
get_age: func() {return age;},
set_name: func(n){name=n;},
get_name: func() {return name;}
};
}
Trait
Also there's another way to OOP, that is trait.
When a hash has a member named parents and the value type is vector,
then when you are trying to find a member that is not in this hash,
virtual machine will search the member in parents.
If there is a hash that has the member, you will get the member's value.
Using this mechanism, we could OOP like this, the result is 114514:
var trait={
get:func{return me.val;},
set:func(x){me.val=x;}
};
var class={
new:func(){
return {
val:nil,
parents:[trait]
};
}
};
var a=class.new();
a.set(114514);
println(a.get());
First virtual machine cannot find member set in hash a, but in a.parents there's a hash trait has the member set, so we get the set.
variable me points to hash a, so we change the a.val.
And get has the same process.
And we must remind you that if you do this:
var trait={
get:func{return me.val;},
set:func(x){me.val=x;}
};
var class={
new:func(){
return {
val:nil,
parents:[trait]
};
}
};
var a=class.new();
var b=class.new();
a.set(114);
b.set(514);
println(a.get());
println(b.get());
var c=a.get;
var d=b.get;
println(c());
println(c());
println(d());
println(d());
You will get this result now:
114
514
514
514
514
514
Because a.get will set me=a in the trait.get. Then b.get do the me=b. So in fact c is b.get too after running var d=b.get.
If you want to use this trick to make the program running more efficiently, you must know this special mechanism.
Native functions and module import
This part shows how we add native functions in this interpreter. If you are interested in this part, this may help you. And...
CAUTION: If you want to add your own functions without changing the source code, see the module after this part.
If you really want to change source code, check built-in functions in lib.nas and see the example below.
Definition:
// you could also use a macro to define one.
nas_native(builtin_print);
Then complete this function using C++:
var builtin_print(var* local,gc& ngc)
{
// find value with index begin from 1
// because local[0] is reserved for value 'me'
var vec=local[1];
// main process
// also check number of arguments and type here
// if get an error,use nas_err
for(auto& i:vec.vec().elems)
switch(i.type)
{
case vm_none: std::cout<<"undefined"; break;
case vm_nil: std::cout<<"nil"; break;
case vm_num: std::cout<<i.num(); break;
case vm_str: std::cout<<i.str(); break;
case vm_vec: std::cout<<i.vec(); break;
case vm_hash: std::cout<<i.hash(); break;
case vm_func: std::cout<<"func(..){..}";break;
case vm_obj: std::cout<<"<object>"; break;
}
std::cout<<std::flush;
// generate return value,
// use ngc::alloc(type) to make a new value
// or use reserved reference nil/one/zero
return nil;
}
When running a builtin function, alloc will run more than one time, this may cause mark-sweep in gc::alloc.
The value got before will be collected, but stil in use in this builtin function, this will cause a fatal error.
So use gc::temp in builtin functions to temprorarily store the gc-managed value that you want to return later. Like this:
var builtin_keys(var* local,gc& ngc)
{
var hash=local[1];
if(hash.type!=vm_hash)
return nas_err("keys","\"hash\" must be hash");
// use gc.temp to store the gc-managed-value, to avoid being sweeped
var res=ngc.temp=ngc.alloc(vm_vec);
auto& vec=res.vec().elems;
for(auto& iter:hash.hash().elems)
vec.push_back(ngc.newstr(iter.first));
ngc.temp=nil;
return res;
}
After that, register the built-in function's name(in nasal) and the function's pointer in this table:
struct func
{
const char* name;
var (*func)(var*,gc&);
} builtin[]=
{
{"__print",builtin_print},
{nullptr, nullptr }
};
At last,warp the __print in a nasal file:
var print=func(elems...){
return __print(elems);
};
In fact the arguments that __print uses are not necessary.
So writting it like this is also right:
var print=func(elems...){
return __print;
};
If you don't warp built-in function in a normal nasal function, this native function may cause segmentation fault when searching arguments.
Use import("filename.nas") to get the nasal file including your built-in functions, then you could use it.
Also there's another way of importing nasal files, the two way of importing have the same function:
import.dirname.dirname.filename;
import("./dirname/dirname/filename.nas");
Modules(for lib developers)
If there is only one way to add your own functions into nasal, that is really inconvenient.
Luckily, we have developed some useful native-functions to help you add modules that created by you.
Functions used to load dynamic libraries are added to std/dylib.nas:
var dlopen = func(libname) {
...
}
var dlclose = func(lib) {
...
}
var dlcall = func(ptr, args...) {
...
}
var limitcall = func(arg_size = 0) {
...
}
As you could see, these functions are used to load dynamic libraries into the nasal runtime and execute. Let's see how they work.
First, write a cpp file that you want to generate the dynamic lib, take the fib.cpp as the example(example codes are in ./module):
// add header file nasal.h to get api
#include "nasal.h"
double fibonaci(double x) {
if (x<=2) {
return x;
}
return fibonaci(x-1)+fibonaci(x-2);
}
// module functions' parameter list example
var fib(var* args, usize size, gc* ngc) {
if (!size) {
return nas_err("fib", "lack arguments");
}
// the arguments are generated into a vm_vec: args
// get values from the vector that must be used here
var num = args[0];
// if you want your function safer, try this
// nas_err will print the error info on screen
// and return vm_null for runtime to interrupt
if(num.type!=vm_num) {
return nas_err("extern_fib", "\"num\" must be number");
}
// ok, you must know that vm_num now is not managed by gc
// if want to return a gc object, use ngc->alloc(type)
// usage of gc is the same as adding a native function
return var::num(fibonaci(num.tonum()));
}
// then put function name and address into this table
// make sure the end of the table is {nullptr,nullptr}
module_func_info func_tbl[] = {
{"fib", fib},
{nullptr, nullptr}
};
// must write this function, this will help nasal to
// get the function pointer by name
// the reason why using this way to get function pointer
// is because `var` has constructors, which is not compatiable in C
// so "extern "C" var fib" may get compilation warnings
extern "C" module_func_info* get() {
return func_tbl;
}
Next, compile this fib.cpp into dynamic lib.
Linux(.so):
clang++ -c -O3 fib.cpp -fPIC -o fib.o
clang++ -shared -o libfib.so fib.o
Mac(.so & .dylib): same as Linux.
Windows(.dll):
g++ -c -O3 fib.cpp -fPIC -o fib.o
g++ -shared -o libfib.dll fib.o
Then we write a test nasal file to run this fib function, using os.platform() we could write a cross-platform program:
import.std.dylib;
var dlhandle = dylib.dlopen("libfib."~(os.platform()=="windows"?"dll":"so"));
var fib = dlhandle.fib;
for(var i = 1; i<30; i+=1)
println(dylib.dlcall(fib, i));
dylib.dlclose(dlhandle.lib);
dylib.dlopen is used to load dynamic library and get the function address.
dylib.dlcall is used to call the function, the first argument is the function address, make sure this argument is vm_obj and type=obj_extern.
dylib.dlclose is used to unload the library, at the moment that you call the function, all the function addresses that got from it are invalid.
dylib.limitcall is used to get dlcall function that has limited parameter size, this function will prove the performance of your code because it does not use vm_vec to store the arguments, instead it uses local scope to store them, so this could avoid frequently garbage collecting. And the code above could also be written like this:
import.std.dylib;
var dlhandle = dylib.dlopen("libfib."~(os.platform()=="windows"?"dll":"so"));
var fib = dlhandle.fib;
var invoke = dylib.limitcall(1); # this means the called function has only one parameter
for(var i = 1; i<30; i+=1)
println(invoke(fib, i));
dylib.dlclose(dlhandle.lib);
If get this, Congratulations!
./nasal a.nas
1
2
3
5
8
13
21
34
55
89
144
233
377
610
987
1597
2584
4181
6765
10946
17711
28657
46368
75025
121393
196418
317811
514229
832040
Difference Between Andy's and This Interpreter
Must use `var` to define variables
This interpreter uses more strict syntax to make sure it is easier for you to program and debug.
And flightgear's nasal interpreter also has the same rule.
So do not use variable without using var to declare it.
In Andy's interpreter:
foreach(i;[0,1,2,3])
print(i)
This program can run normally.
But take a look at the iterator i,
it is defined in foreach without using keyword var.
I think this design will make programmers feeling confused that they maybe hard to find the i is defined here.
Without var, they may think this i is defined anywhere else.
So in this interpreter i use a more strict syntax to force users to use var to define iterator of forindex and foreach.
If you forget to add the keyword var, you will get this:
code: undefined symbol "i"
--> test.nas:1:9
|
1 | foreach(i;[0,1,2,3])
| ^ undefined symbol "i"
code: undefined symbol "i"
--> test.nas:2:11
|
2 | print(i)
| ^ undefined symbol "i"
Trace Back Info
When interpreter crashes, it will print trace back information:
Native function `die`
Function die is used to throw error and crash immediately.
func()
{
println("hello");
die("error occurred this line");
return;
}();
hello
[vm] error: error occurred this line
[vm] native function error.
trace back:
0x000000ac 40 00 00 00 25 callb 0x25 <__die@0x41afc0> (lib.nas:131)
0x000004f6 3e 00 00 00 01 callfv 0x1 (a.nas:4)
0x000004fa 3e 00 00 00 00 callfv 0x0 (a.nas:6)
vm stack (0x7fffcd21bc68 <sp+80>, limit 10, total 12):
0x0000005b | null |
...
0x00000057 | str | <0x138ff60> error occurred t...
...
0x00000052 | nil |
Stack overflow
Here is an example of stack overflow:
func(f){
return f(f);
}(
func(f){
f(f);
}
)();
[vm] stack overflow
trace back:
0x000004fb 3e 00 00 00 01 callfv 0x1 (a.nas:5)
0x000004fb 1349 same call(s)
0x000004f3 3e 00 00 00 01 callfv 0x1 (a.nas:2)
0x000004ff 3e 00 00 00 01 callfv 0x1 (a.nas:3)
vm stack (0x7fffd3781d58 <sp+80>, limit 10, total 8108):
0x00001ffb | func | <0x15f8d90> entry:0x4f9
0x00001ffa | func | <0x15f8d90> entry:0x4f9
0x00001ff9 | pc | 0x4fb
...
0x00001ff2 | addr | 0x7fffd37a16e8
Normal vm error crash info
Error will be thrown if there's a fatal error when executing:
func(){
return 0;
}()[1];
[vm] callv: must call a vector/hash/string
trace back:
0x000004f4 3b 00 00 00 00 callv 0x0 (a.nas:3)
vm stack (0x7fffff539c28 <sp+80>, limit 10, total 1):
0x00000050 | num | 0
Detailed crash info
Use command -d or --detail the trace back info will show more details:
hello
[vm] error: error occurred this line
[vm] error: native function error
trace back (main)
0x000000b0 40 00 00 00 2b callb 0x2b <__die@0x41c380> (lib.nas:131)
0x00000553 3e 00 00 00 01 callfv 0x1 (test.nas:4)
0x00000557 3e 00 00 00 00 callfv 0x0 (test.nas:6)
vm stack (0x7fffe0ffed90 <sp+63>, limit 10, total 12)
0x0000004a | null |
0x00000049 | pc | 0x553
0x00000048 | addr | 0x7fffe0ffeda0
...
0x00000041 | nil |
registers (main)
[ pc ] | pc | 0xb0
[ global ] | addr | 0x7fffe0ffe9a0
[ localr ] | addr | 0x7fffe0ffedf0
[ memr ] | addr | 0x0
[ canary ] | addr | 0x7fffe1002990
[ top ] | addr | 0x7fffe0ffee40
[ funcr ] | func | <0x677cd0> entry:0xb0
[ upvalr ] | nil |
global (0x7fffe0ffe9a0 <sp+0>)
0x00000000 | func | <0x65fb00> entry:0x5
0x00000001 | func | <0x65fb20> entry:0xd
...
0x0000003d | func | <0x66bf00> entry:0x51f
0x0000003e | hash | <0x65ffa0> {5 val}
local (0x7fffe0ffedf0 <sp+45>)
0x00000000 | nil |
0x00000001 | str | <0x6cb630> error occurred t...
Debugger
We added a debugger in v8.0.
Use command ./nasal -dbg xxx.nas to use the debugger,
and the debugger will print this:
Click to unfold
source code:
--> var fib=func(x)
{
if(x<2) return x;
return fib(x-1)+fib(x-2);
}
for(var i=0;i<31;i+=1)
print(fib(i),'\n');
next bytecode:
--> 0x00000000 01 00 00 00 41 intg 0x41 (test/fib.nas:0)
0x00000001 0b 00 00 00 05 newf 0x5 (lib.nas:6)
0x00000002 02 00 00 00 02 intl 0x2 (lib.nas:6)
0x00000003 0f 00 00 00 00 dyn 0x0 ("elems") (lib.nas:6)
0x00000004 32 00 00 00 07 jmp 0x7 (lib.nas:6)
0x00000005 40 00 00 00 00 callb 0x0 <__print@0x419c80> (lib.nas:7)
0x00000006 4a 00 00 00 00 ret 0x0 (lib.nas:7)
0x00000007 03 00 00 00 00 loadg 0x0 (lib.nas:6)
vm stack (0x7fffd0259138 <sp+65>, limit 10, total 0)
>>
If want help, input h to get help.
When running the debugger, you could see what is on stack. This will help you debugging or learning how the vm works:
Click to unfold
source code:
var fib=func(x)
{
--> if(x<2) return x;
return fib(x-1)+fib(x-2);
}
for(var i=0;i<31;i+=1)
print(fib(i),'\n');
next bytecode:
0x00000548 0c 00 00 00 aa happ 0xaa ("running") (lib.nas:503)
0x00000549 03 00 00 00 3e loadg 0x3e (lib.nas:498)
0x0000054a 0b 00 00 05 4e newf 0x54e (test/fib.nas:1)
0x0000054b 02 00 00 00 02 intl 0x2 (test/fib.nas:1)
0x0000054c 0d 00 00 00 1b para 0x1b ("x") (test/fib.nas:1)
0x0000054d 32 00 00 05 5d jmp 0x55d (test/fib.nas:1)
--> 0x0000054e 39 00 00 00 01 calll 0x1 (test/fib.nas:3)
0x0000054f 2d 00 00 00 03 lessc 0x3 (2) (test/fib.nas:3)
vm stack (0x7fffd0259138 <sp+65>, limit 10, total 7)
0x00000047 | pc | 0x566
0x00000046 | addr | 0x0
0x00000045 | nil |
0x00000044 | num | 0
0x00000043 | nil |
0x00000042 | nil |
0x00000041 | func | <0x88d2f0> entry:0x5
>>
REPL
We added experimental repl interpreter in v11.0. Use this command to use the repl interpreter:
nasal -r