Source Code Format

Written by Elmar Vogt, Fürth, GERMANY

Here you learn about the basics of BASIC, so to speak. This chapter deals with the way a SmallBASIC program composed.

A program consists of a single source file. It is possible to include libraries from external source files with the Unit-mechanism.

Source files are simple text files. They can be written in ASCII or UTF-8.

The basic program component is a line of text, ending with _CR or _LF/CR characters.¹

SmallBASIC is case-insensitive: The names myvar and MyVar will always refer to the same variable or function. Likewise, keywords are case-insensitive: Both print and PRINT are legal variants of the same command.

Whitespace – i.e., non-printing characters like spaces and tabs – is ignored in SmallBASIC, except inside string literals where it is retained. ²

for a = 0 to 10

for a=0to 10

But note that the omission of whitespace can lead to parsing errors: If the above line were abbreviated to

fora=0to10

this would cause an error, because for and to wouldn’t be recognized as keywords anymore. Rather, SmallBASIC would consider fora and to10 to be variable names.³

Each program line contains one or more commands. Multiple commands on a line are separated by a colon _:.

print "Hello world!"
print "Wonderful day."

print "Hello world!" : print "Wonderful day."

Line continuation: If the ampersand _& is the last character on a line, then the interpreter will assume that the current command extends to the next line as well.

X = 245 * 198 - sqr(5)

X = 245 * 198 &
        - sqr(5)

Literals

Numbers

Numbers can be written in the usual manner, using either _conventional or scientific notation. All of the following examples are legal numbers in:

1, 0, -1, 1.2, -23232.5, 1.902e-50, -.423

As is shown in the last example, numbers with an absolute value _<1 need not be preceded with ₀.

Integer numbers can also be represented in hexadecimal, octal and binary notation with various prefixes:

hexadecimal: _&h, _0h, _&x, or _0x

octal: _&o or _0o

binary: _&b (or _0b)

&hAFFE0815, &o4242, &b100101011
0hAFFE0815, 0o4242, 0b100101011

String literals

String literals are character sequences which are to be treated as program data _as is, not as variable or keyword names. String literals are bracketed by double quotes _".

"This is a string literal"
this will be considered as a sequence of keywords

Note that when a string literal is to be extended across more than one line, it must be properly closed before the continuation ampersand and re-opened on the subsequent line with the _" delimiter character:

print "Hello &
        world!"     ' error

print "Hello " &
        "world!"        ' correct

Identifiers

Identifiers – _names for variables and functions – follow the usual conventions:

They consist of a letter or an underscore _{_}, followed by one or more of the following:

• other letters

• digits (₀ – ₉)

• the underscore _{_}

• the dollar sign _$ (only as the last character of the identifier, see below)

A single underscore _{_} is a legal complete identifier.

Identifiers can have virtually unlimited length. All characters are significant in resolving an identifier (ie, to determine whether two identifiers refer to the same variable.)⁴

Traditionally, in BASIC the dollar sign $ serves as a signal to indicate that a name identifies a string variable, if used as the last character of the identifier (i.e., my_name$).

Since SmallBASIC is a typeless language (see below) where variables can hold values of any type, such a signal would be misleading, yet it has been retained for the sake of compatibility. It may be placed as the last character of an identifier only. Here it serves two distinguish between identifiers (harry and harry$ are two different identifiers), but has otherwise no function.

Comments

Line comments can be introduced in three ways:

• With the keyword rem,

• With the apostrophe character _’,

• With a hash sign _#.

Everything on the current line following the comment introduction will be ignored in program execution.

If the rem keyword is used and it is preceded by other commands on the current line, it must be separated from the previous commands by a colon _: If the hash sign is used, it must be the first character on the line.

for a=0 to 10      ' this is a valid comment
   print a         : rem this also
# this is a whole line commented out
next a
rem the last comment

print "Hello world!"   rem vain commenting attempt

The rem in the last line above will cause an error, because it needs to be preceded with a colon _:.

There are no provision for block comments.