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ValKmjolnir edited this page May 16, 2024 · 12 revisions

Tutorial

Nasal is easy to learn. After reading this tutorial about 15 minutes, You could totally use nasal.

Contents

How to Use

First we should learn how to write and run a program using this language, click to see the tutorial.

Input this command to run scripts directly:

./nasal filename

Use these commands to get version of interpreter:

./nasal -v | --version

       __                _
    /\ \ \__ _ ___  __ _| |
   /  \/ / _` / __|/ _` | |
  / /\  / (_| \__ \ (_| | |
  \_\ \/ \__,_|___/\__,_|_|

ver  : 11.2 linux x86-64 (May 15 2024 22:52:48)
std  : c++ 201703
core : 4 core(s)
repo : https://github.com/ValKmjolnir/Nasal-Interpreter
repo : https://gitee.com/valkmjolnir/Nasal-Interpreter
wiki : https://wiki.flightgear.org/Nasal_scripting_language

presented by fgprc members - http://fgprc.org.cn

input <nasal -h> to get help .

Use these commands to get help(see more debug commands in help):

./nasal -h | --help

     ,--#-,
<3  / \____\  <3
    |_|__A_|

nasal <option>
option:
   -h,   --help     | get help.
   -v,   --version  | get version.
   -r,   --repl     | use repl interpreter(experimental).

nasal [option] <file> [argv]
option:
   -a,   --ast      | view ast after link/optimize process.
         --raw-ast  | view ast without after-processing.
   -c,   --code     | view generated bytecode.
   -s,   --symbol   | show analysed symbol info.
   -e,   --exec     | execute directly.
   -t,   --time     | show execute time.
   -d,   --detail   | get detail info.
   -f,   --ref-file | get referenced files.
   -dbg, --debug    | debug mode.
         --prof     | show profiling result, available in debug mode.
         --prof-all | show profiling result of all files, available under debug mode.
         --limit    | use limited execution mode (readonly api enabled).
file:
   <filename>       | execute file.
argv:
   <args>           | cmd arguments used in program.

If your system is Windows and you want to output unicode,please use this command before running nasal interpreter:

chcp 65001

or you could write this in your nasal code:

if(os.platform()=="windows")
    system("chcp 65001");

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.

ghost 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

Nasal has many special global symbols:

globals; # hashmap including all global symbols and their values
arg;     # in global scope, arg is the command line arguments
         # in local scope, arg is the dynamic arguments of this function call

For example:

var a = 1;
println(globals); # will print {a:1}
# nasal a b c
println(arg); # will print ["a", "b", "c"]

func() {
    println(arg);
}(1, 2, 3);   # will print [1, 2, 3]

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.

Multi-Files/Modules Import

See more details in namespace.md

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.
var builtin_print(context*, gc*);

Then complete this function using C++:

var builtin_print(context* ctx, gc* ngc) {
    // find value with index begin from 1
    // because local[0] is reserved for value 'me'
    for(auto& i : ctx->localr[1].vec().elems) {
        std::cout << i;
    }
    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(context* ctx, gc* ngc) {
    auto hash = ctx->localr[1];
    if (hash.type!=vm_hash && hash.type!=vm_map) {
        return nas_err("keys", "\"hash\" must be hash");
    }
    // use gc.temp to store the gc-managed-value, to avoid being sweeped
    auto res = ngc->temp = ngc->alloc(vm_vec);
    auto& vec = res.vec().elems;
    if (hash.type==vm_hash) {
        for(const auto& iter : hash.hash().elems) {
            vec.push_back(ngc->newstr(iter.first));
        }
    } else {
        for(const auto& iter : hash.map().mapper) {
            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:

nasal_builtin_table 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:

use dirname.dirname.filename;
import("./dirname/dirname/filename.nas");

C++ 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
NASAL_EXTERN 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:

use 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:

use 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

Ghost Type (for lib developers)

It's quite easy to create a new ghost by yourself now. Look at the example below:

const auto ghost_for_test = "ghost_for_test";

// declare destructor for ghost type
void ghost_for_test_destructor(void* ptr) {
    std::cout << "ghost_for_test::destructor (0x";
    std::cout << std::hex << reinterpret_cast<u64>(ptr) << std::dec << ") {\n";
    delete static_cast<u32*>(ptr);
    std::cout << "    delete 0x" << std::hex;
    std::cout << reinterpret_cast<u64>(ptr) << std::dec << ";\n";
    std::cout << "}\n";
}

var create_new_ghost(var* args, usize size, gc* ngc) {
    var res = ngc->alloc(vm_obj);
    // create ghost type
    res.ghost().set(ghost_for_test, ghost_for_test_destructor, new u32);
    return res;
}

var set_new_ghost(var* args, usize size, gc* ngc) {
    var res = args[0];
    if (!res.object_check(ghost_for_test)) {
        std::cout << "set_new_ghost: not ghost for test type.\n";
        return nil;
    }
    f64 num = args[1].num();
    *(reinterpret_cast<u32*>(res.ghost().pointer)) = static_cast<u32>(num);
    std::cout << "set_new_ghost: successfully set ghost = " << num << "\n";
    return nil;
}

var print_new_ghost(var* args, usize size, gc* ngc) {
    var res = args[0];
    // check ghost type by the type name
    if (!res.object_check(ghost_for_test)) {
        std::cout << "print_new_ghost: not ghost for test type.\n";
        return nil;
    }
    std::cout << "print_new_ghost: " << res.ghost() << " result = "
              << *((u32*)res.ghost().pointer) << "\n";
    return nil;
}

We use this function to create a new ghost type:

void nas_ghost::set(const std::string&, nasal::nas_ghost::destructor, void*);

const std::string& is the name of the ghost type.

nasal::nas_ghost::destructor is the pointer of the destructor of the ghost type.

void* is the pointer of the ghost type instance.

And we use this function to check if value is the correct ghost type:

bool var::object_check(const std::string&);

The parameter is the name of the ghost type.

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