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DBASIC Language specification

Design principles

  • All keywords are written in UPPERCASE.
  • Statements and Declarations are terminated with newlines (note with ';' like in many other languages)
  • Special keywords are used the specify code-blocks (instead of {}). For example THEN and END for the blocks of IF-Statements
  • Variables are statically typed and type-checking is strickt. No implicit type conversions happen.
  • As the language is intended as an easy target for practicing compiler design only basic features exist.

Programm structure

On the top-level all DBASIC programms consist of functions and global variables. All programms MUST contain a function called "main" without arguments and with return-type INT.

Global variables

Global variables are declared using the global keyword.

GLOBAL INT i = 5

Functions

Functions are declared using the FUNC keyword.

FUNC funcname(INT arg1, BOOL arg2) INT
//body
RETURN 0
END

Functions can have 0 to 6 arguments. The return type-is optional. Functions without return-type return nothing. Each function-body MUST end with a RETURN statement before the END.

External functions (like the ones from glibc) can be called. No type-checking happens for such functions.

Variables can not be of type string, but string-constants can be used as arguments to builtin and C functions. The following call is completely valid.

puts("HELLO WORLD")

Builtin functions

There are some special builtin functions available.

  • input() reads a number from stdin and returns it as INT
  • print("format",arg0,argn) functions exactly like C's printf. The first argument is a fromat string and all following arguments fill the placeholders in the format-string.
FUNC main() INT
INT x = input()
print("Your entered %d\n",x)
END

Control-Flow

If statements:

IF condition THEN
//code
ELSE
//code
END

The else-block is optional. The condition must be an expression of type BOOL.
For example, if x is of type INT: IF x == 3 THEN is valid, but IF x THEN is not.

While-loops are the only supported kind of loops.

WHILE condition DO
//code
END

Like for if-statements condition must be of type BOOL.

Variables

Variables can be of type INT (signed) or BOOL. Variables must be declared before use. A default value MUST be assigned during declaration. The type is only specified during the inital declaration. Variable types are checked at compile time. For example trying to assign a boolean value to an INT variable will fail with a compiler error.

INT i = 0
INT q = i+3
i = 10

Arithmetics

The following operations are defined for INTs and also return INTs:

  • i+j Addition
  • i-j Subtraction
  • i*j Multiplication
  • i/j Division
  • -i Negation
  • i|j bitwise or
  • i&j bitwise and

Comparisons are defined for INTs and return BOOLs

  • ==
  • !=
  • >=
  • <=
  • >
  • <

Equal and not equal are also defined for BOOLs.

Normal order of operations is honored. Also brackets can be used to clarify operation order.

INT i = 1
INT j = 2
INT q = i+j*i+(2*i)
BOOL f = i==j
BOOL z = TRUE

Function calls to non-external functions with a return-type other then None can also be used in calculations. The special keywords TRUE and FALSE can be used to initialize BOOL variables.