JBASIC

Simple Interpreter for the JBASIC programming language written in Java using ANTLR.

JBASIC is a simple general purpose, high-level scripting language heavily inspired by the earliest dialects of BASIC.

Table of Contents

• Overview
• Operators
• Keywords
• Functions
• Building
• How it works
• License

Overview

JBASIC is dialect of 'BASIC' (Beginners' All-purpose Symbolic Instruction Code) a family of general-purpose, high-level programming languages, that focus on ease of use. The original version of BASIC was created in 1963 at the Dartmouth College, by John G. Kemeny and Thomas E. Kurtz.

JBASIC combines traits of the first and the second generation of basic languages.

Usage:

java -jar JBASIC.jar <filePath>

Operators

Binary operators

Operator	Description	Example
+	Computes the sum of two numerical values or concatenates two strings.	1 + 2 // 3
-	Subtracts the second value from the first value.	2 - 1 // 1
*	Multiplies the two values.	3 * 3 // 9
/	Divides the first value with the second value.	9 / 3 // 3
<	Less than	1 < 2 // 1
<=	Less than equal.	1 <= 2 // 1
>	Greater than	1 > 2 // 0
>=	Greater than equal.	1 >= 2 // 0
=	Comparison for equality of two values. 1 if they are equal 0 if not	9 = 3 // 0
<>	Comparison for equality of two values. 0 if they are equal 1 if not	9 <> 3 // 1

Unary operators

Operator	Description	Example
-	Negates a numerical value.	-5

Keywords

The language features the following keywords

Data manipulation

Keyword	Description	Example
DATA ...	holds a list of values which are assigned sequentially using the READ command	DATA 1, 2, 3, 4, 5
DIM	Creates a new array with the specified dimensions	DIM array[3]
LET	Assigns a value (which may be the result of an expression) to a variable.	LET I = 1
READ ...	Reads a value from a DATA statement and assigns it to a variable and moves it one position forward with each READ. Multiple variables can be specified as parameters to read several values in a single operation.	READ A, B
RESTORE	Resets to the DATA statement to the specified index, allowing the program to begin READing from the value at the specified index.	RESTORE 0

If the variable name in a Let statement ends with '$' the assigned value needs to be a string and if it ends with '%' a numerical value.

LET ASTRING$ = "Hello World"
LET ANUMBER% = 10

An array in JBASIC can be either one-, two- or three-dimensional. A specific value in the array can be accessed or altered by specifying the index. The first element in an array has the index '1', like in most other dialects of BASIC.

DIM array[3]
array[1] = "Hello"
array[2] = " World!"
PRINT array[1] + array[2]

If the array name in a DIM statement ends with '$' it can only store strings and if it ends with '%' it can only store numerical values.

Input and output

Keyword	Description	Example
CLS	Clears the screen	CLS
INPUT	Asks the user to enter the value of a variable. The statement may include a prompt message	INPUT "NAME= ", name
PRINT	Displays a message on the screen or other output device	PRINT "Hello World!"

Logical

Keyword	Description	Example
NOT	Inverts a logical value.	NOT 1 // 0

Mathematical

Keyword	Description	Example
MOD	Returns the remainder of the division of the first value with the second value	5 MOD 3 // 2

Miscellaneous

Keyword	Description	Example
REM	holds a programmer's comment or remark used to help identify the purpose of a given section of code	REM This is a remark / comment

Program flow control

Keyword(s)	Description	Example
IF ... THEN ... {ELSE IF} ... {ELSE} ... END	Used to perform comparisons or make decisions.	IF 1 < 2 THEN  print "true" ELSE  print "false" END
FOR ... TO ... {STEP} ... NEXT	Repeats a section of code a given number of times.	FOR I = 0 TO 5  print I NEXT
WHILE ... ... END	Repeats a section of code a given number of times.	WHILE I < 2  print I  I = I + 1 END
REPEAT ... UNTIL ...	Repeats a section of code a given number of times.	REPEAT  print I  I = I + 1 UNTIL I > 4
DO ... WHILE ...	Repeats a section of code a given number of times, but at least once.	DO  print I  I = I + 1 WHILE I < 2
DO ... UNTIL ...	Repeats a section of code a given number of times, but at least once.	DO 1 < 2  print I  I = I + 1 UNTIL I > 4
SWITCH ... (CASE ... : ...)+ END	Allows the use of the value of a variable or expression to change the program execution via search and map.	SWITCH 1 + 2  CASE 1: "one"  CASE 2: "two"  CASE 3: "three" end
GOTO	Jumps to a numbered or labelled line in the program.	10: PRINT "Hi" 20: GOTO 10

Subroutine specific

JBASIC allows the definition of subroutines to accomplish a particular task.

Keyword(s)	Description	Example
CALL(...)	Calls a subroutine	CALL printSum(1, 2)
SUB(...) ... END SUB	Defines a new subroutine	SUB printSum(a, b)  PRINT a + b END

An example for a simple subroutine would be:

SUB Greet()
   INPUT "Name=" name
   PRINT "Hi my name is " + name
END SUB

CALL Greet()

The SUB keyword marks the definition of a subroutine. After that the name of the subroutine and the arguments of the subroutine are specified. Then the body of the subroutine follows. The end of the subroutine is marked with the END and the SUB keyword. Subroutines are then invoked using the call keyword.

Functions

JBASIC offers numerous built-in functions to perform various tasks.

Mathematical

FunctionName	Description	Example Usage
ABS	Absolute value	ABS(-2) // 2
ACS	Arc cosine	ACS(0) // 1.5707963267949
ASH	Arc sine hyperbolicus	ASH(1.1752011936438) // 1
ASN	Arc sine	ASN(1) // 1.5707963267949
ATH	Area tangent hyperbolicus	ATH(1) // ∞
ATN	Arc tangent	ATN(1) // 0.78539816339745
AVG	Average	AVG(1, 2, 3) // 2
COS	Cosine	COS(1.5707963267949) // 0
EXP	Exponential function	EXP(1) // 2,7182818284590452353602874713527
LOG	Natural logarithm	LOG(2,7182818284590452353602874713527) // 1
MAX	Maximum value	MAX(1, 2, 3) // 3
MIN	Minimum value	MIN(1, 2, 3) // 1
SIN	Sine (argument in radians)	SIN(1.5707963267949) // 1
SQR	Square root	SQR(9) // 3
SUM	Summation	SUM(1, 2, 3) // 6
TAN	Tangent	TAN(0.78539816339745) // 1

Miscellaneous

Function	Description	Example Usage
LIST	Creates a string that contains the full source code of the current program	LIST() // LIST()
NUM	Converts a string to a numerical value	NUM("3") // 3
RND	Creates a random number in the specified range	RND(1, 3) // [1 .. 3]
STR	Converts a numerical value to a string	STR(3) // "3"

Strings

FunctionName	Description	Example Usage
LEN	Length of a string	LEN("123") // 3

Building

The interpreter is built using maven and uses the JDK version 11.

How it works

The interpretation of a program is performed in the following stages:

• Lexical analysis: We iterate over all the characters in the source code and group them together to tokens
• Parsing: Next we parse the linear sequence of tokens we have created in the previous step to create an abstract syntax tree
• Execution: To execute a JBASIC program we visit all the nodes in our abstract syntax tree and evaluate them

More information about the interpreter can be found at the technical documentation.

License

This project is licensed under the GNU General Public License