LanguageFeatures

BScript is a JavaScript-like language, with similar syntax, scoping rules and closures.

Literals

• Basic types: numbers, strings, boolean, null. All numbers are floats but are cast to int if needed (array lookups, pixel coordinates, etc.)
• Arrays: [1, 'a'] Arrays can contain any other type. To append to an array, add an element to an index past the length of the array.
• Maps: { "a": 1, "b": "c" } Map keys are always strings. Map elements can be looked up by the map["a"] or map.a notation.
• Functions: x => x + 1 Functions are first-class types.
• Numerical expressions support the usual arithmetic operations, plus % for modulo.

Constants and variables

• Constants can only be declared outside of functions: const PI = 3.14159;
• Variables can be global (outside of functions), local (in a function) or function parameters: x := 42;. Variable scope starts in the local function and travels out toward the global scope.

Functions

• Define named functions via def square(n) { return n * n; }.
• Function can take other functions as a parameter, or return a function.
• Functions can be declared in another function.
• Anonymous functions are declared via: x => x + 1 or (x,y) => { return x + y; }
• Functions are evaluated in the context of their closure. For example:

def x() {
   localVar := 1;
   return b => localVar + b;
}

fx := x();
print(fx(5));

will print 6.

• map values can be functions that take a special first argument (usually called "self" or "this") that points to the map that contains them. For example:

player := {
   "isAlive": self => self.lives > 0,
   "lives": 3,
};
trace(player.isAlive());

Control flow commands

• if(x) { ... } if else(y) { ... } else { ... } if statement works like you think it does. The else clause is optional.
• BScript only has one type of loop: while(x < 10) { ... }
• Both if and while support the following conditional operations: =, !=, <, <=, >, >=.
• More complex boolean logic can be expressed with and: && and or || operators. (These use short-circuit evaluation.)
• The return <value> statement always needs a value to return.

Other built-in commands

• To delete from an array or map, use del a[10]. In this case it would delete the 10th element in the array. The array/map reference can be arbitrarily complex. For example: del game.enemies()[4].inventory[5]
• See the BuiltinFunctions and BuiltinConstants pages for more info.
• # this is a comment Comments are allowed anywhere except inside literals (this may change soon.)
• Bscript programs can use the following built-in functions:
  • Array functions: array_map, array_join, array_filter, array_find, array_find_index, array_foreach, choose, basic_sort, basic_sort_copy, array_reverse, array_reduce, array_remove, copy_array, array_times, array_concat, array_flatten
  • Other functions: copy_map, roll, normalize, endsWith, startsWith, asPercent, range, pow

Program execution

• Code execution starts by running the main method.
• Your program can be a single .b file, or a single directory containing any number of .b files.
• In the latter case, every file in the directory is parsed and joined to produce the program.
• When running code from directory, your code can load and save map type objects to/from files. Filenames must be a string with no path characters (., .., /, \ are not allowed)