(not JavaScript)
This is a simple script language that I wrote a few years ago for educational purpose.
This language is first designed to find the mathematical derivatives (including partial derivatives) of mathematical functions. For example, if there is two variable x and y, and we define functions u:=sin(x)*y, v:=x*cos(y), f:=u+v, it can easily find the mathematical form of df/dx (=y*cos(x)+cos(y)), df/dy (=sin(x)-x*sin(y)) using chain rule.
This language can also be used for general purposes. It has control structures such as if/while/for. It also has strings and arrays (may be multi-dimensional) and functions!
Some weaknesses of this language: It is not good at detecting syntax error. If the code is not well written, the interpreter may not give any informative message and may simply crash. This is due to the insufficient lexical analysis and parse tree building. The code is also not optimized for performance.
However, there is no obvious bug in the interpreter, so it is still usable.
There is an example in /examples folder, which is a tic-tac-toe game written in J-Script.
- Interactive mode: simply double click the
J-Script.exefile - Script mode: enter command
J-Script.exe <script_name>.jsc
Use keyword var to define a variable
- define a variable without initialization：
var a;
- define multiple variables without initialization：
var a,b,c;
- define variable with initialization：
var a = 1;
var b = 1+3*2, c, d = 4-9;
var e = (a+b)*2; #can use other variables to initialize
Each statement ends with a semicolon ( ;).
You can put multiple statements in a single line.
contents after # in a line is treated as comments.
Use keyword str to define strings
str s;
str s1,s2,s3;
str s1 = "aa", s2;
Node that there is no `+` operations implemented for strings：
str s1 = "aa"+"bb"; #error
arithmetic operators：
+ - * / % ^
(note that no integer division for /)。
a^b means raise a to bth power
^ has higher precedence to */%。
comparation operators：
== != < > <= >=
logic operators:
|| &&
not()
assignment oprator：
=
examples:
a = 1;
s1 = "string";
b = func(1,2,3); #functions are introduced in later chapters
Arrays can store any type, including other arrays.
Array is 0-indexed.
Use keyword `arr` to define arrays
1.define empty arrays
arr array;
arr array1,array2,array3;
# arrays defined in this way have length 0.
2.define arrays with initial size
arr array[initialSize];
For example：
arr array[10]; #array has 10 null elements
arr array1[5+8], array2[a+3]; #can use expression as array's initial size。
3.define multi-dimensional array
For example：
arr doubleArray[2,3];
# create an 2*3 array，whose elements are all null
# = { { null, null, null }, { null, null, null } }
It is also possible to define arrays with more dimensions, split by colon:
arr triArray[4,5,6], quaArray[2,3,4,5];
4.Assign a value to an element in array
array[index] = value;
For example：
array[2] = 3; #assign 3 to the item 2 (0-indexed) in the array
doubleArray[0,1] = 4;
5.Use append to add elements to array at back
#Suppose array = {0,1}
append array 2；
#Now array = {0,1,2};
If you omit the argument after `array`, a `null` will be appended.
append array;
#Now array = {0,1,2,null};
Use inputNum function to get a numeric input from stdin：
inputNum(a);
Note: There is no support for `inputNum(array[index])` for now
Use print function to output values to stdout：
When use print to display the value of a variable, you need to use with eval. Otherwise, it will simply print the name of the variable.
var a = 2;
print(a);#display a
print(eval(a));#display 2
print(eval(a+2));#display 4
#str s = “abc“;
print(s); #display abc
print can take multiple arguments, seperated by colons.
print("a = ",eval(a),"\n");
print("array = ",array);
Conditions
The expression below are all examples of valid conditions.
true
false
winner == X
i<L && winner==0 || false
not(1 == 2)
true and false are keywords.
Use not(condition) to inverse a condition
if(condition)
{
statements
};
if(condition){
statements
}else{
statements
};
if(condition_1){
statements
}elif(condition_2){ #there can be any numbers of elif blocks
statements
}else{
statements
};
#Note the semicolon at the end of the blocks
while(condition)
{
statements
};
for(initialization;(condition);end_of_block)
{
statements
};
For example:
for(var i = 0;(i<3);i=i+1)
{
for((var j = 0),(j<3),(j=j+1))
{
board[i,j] = 0;
};
break;
};
Note that you must use an extra pair of parathesis around the condition.
And you can use the statement break; to jump out from the inner-most while/for block.
Use keyword proc to define functions. You need to specify the type of input arguments in the function's definition, but you don't need to specify the return type.
proc can take var, str, arr, proc, func (introduced later) types as arguments.
use return <expression> to return a number from function.
use return obj to return an str，arr，func，proc from function
Example 1:
proc getNum(str prompt,var low,var high)
{
var result = 0;
print(prompt);
while(true)
{
inputNum(result);
if(result>=low && result<=high){break;};
print("please input",eval(low),"to",eval(high),":");
};
return result; #return a number
};
Example 2:
proc initlines()
{
arr lines[8,3,2];
return obj lines; #return an reference to an array
#note that it is not destroyed when function ends
};
You can define function in function, and return function from function A function defined in an other function can access arguments of its parent function。
Example 3:
proc make_adder(var a)
{
proc adder(var b)
{
return a+b;
};
return obj adder;
};
proc add3 = make_adder(3); #Use keyword proc to initialize add3 to the return value
var five = add3(2);
print(eval(five)); #display 5
print(...), inputNum(arg),
sin(arg),cos(arg),tan(arg),exp(arg),ln(arg),log(num,base)
deriv(func,var) #introduced in later chapter
The initial purpose of this language is to compute the mathematical derivitives of multivariable functions.
Use keyword func to define a mathematical function. You can only define one math function in a single statement.
var x,y;
func f = x^2;
func g = sin(x)+y/2;
You can use function eval to compute the value of a function:
var x;
func f = x^2;
print(eval(f)); #error: x is not initialized
x = 3;
print(eval(f)); #display 9
Use function deriv to find the mathematical derivitive of a function, which returns a new func object. Usage: deriv(f, x) #computes df/dx
func df = deriv(f,x); #df = 2*x
# the first entry can be any function expression
func dg = deriv(sin(x)+y/2 + f, y); #dg = 0.5
In fact, var is a special case of func, therefore the first entry of deriv can also be a var
deriv(x,x) #=1
deriv(x,y) #=0
This is why you must add eval when you want to display the value of a var, because var is treated the same as func by default.
deriv uses chain rule when there is multiple layers of dependence:
var x,y,t;
func x = 2*t;
func y = t^2;
func z = x*y;
Now,
deriv(z,t) is 2y+x*(2t)
deriv(z,x) is y
deriv(z,y) is x
1. enviro();
print the current enviroment，(all defined var,str,arr,func,proc objects)
2. pause(<prompt>);
pause with a prompt, wait for a key to continue, for example:
pause("press any key to continue");
3. delete(<object>);
delete an object from enviroment, if there are multiple objects with the same name,
then all of them are deleted. Example：
var x = 3;
arr x[2];
delete(x); #delete both var x and arr x