bosslang

A basic Python source-to-source compiler and interpreter for a Pascal-like language.

Usage

$ python exe.py source.boss

$ python -c "from exe import runsource; runsource('program test; begin end.')"

Description

exe.py breaks down the Bosslang source into an Abstract Syntax Tree (AST), reinterprets the output as a syntactically valid Python source and executes it.

Syntax

Program structure

PROGRAM NONAME00;
    VAR a : INTEGER;
BEGIN
    { just a comment }
    a := 1;
END.

Note: Reserved keywords are non-case-sensitive
Note: Variable and function names are alphameric

Supported types

• int() and float() only

var x, y : integer;
var r : real;

• Vectors and matrices also supported!

program matrix;
var mat : integer;
begin
    mat[0][0] := 1;
    mat[0][1] := 2;
    mat[1=1][1=0] := 3;
    mat[CALL(max, 0, 1)][CALL(pow, 1, 1)] := 4;
    CALL(print, mat[1]); { prints mat[1][0] -> 3 }
end.

Note: arrays and matrices have an indefinite size
Note: strings not supported
Note: type checking is ommited

Language constructs

• if statements

if r <> 0 then begin
    if x = 0 then x := 1
    else x := -1;
end;

• while loops

while x > 0 then begin
    CALL(print, x);
    x := x - 1;
end;

Operator precendence

Precedence	Operator	Description
1	[ ]	Array subscripting
2	+ -	Unary plus/minus
3	* / DIV	Multiplication, division, integer division
4	+ -	Binary plus/minus
5	= <> < <= > >=	Relational operators
6	:=	Assignment

Todo: add logical expressions

Functions

returnval := CALL(<function_name> [, args...]);

• Any builtin python or compiler-defined function is callable.

Note: user-defined functions not supported
Note: type incompatible functions return int(0)