libfawk's BASIC: fbas

Libfawk BASIC, fbas (for function-BASIC), is a modern, third-generation dialect of the BASIC language. It features control flow (loops) and functions. Inherited from libfawk, it also supports array-in-array, struct-like array addressing syntax, function references saved in variables and the builtin functions and variables of fawk.

Although there is no GOSUB, fbas still has GOTO and optional line numbering (that can be used mixed with line labeling). This allows traditional (1970s/1980s style) basic programming.

Major differences from the common dialects

• Variable names, parameter names and function names are case-sensitive.
• There is no interactive mode, only stored programs; e.g. there is no LIST command.
• Line numbering is optional. Each line is prefixed with either a line number, an alphanumeric label followed by a colon or has no prerix. Labels and line numbers are used by goto.
• There is no PRINT or INPUT instructions. Use the functions provided by the host app, or use fawk_print() for debug prints. Reason: in most use cases printing directly to stdout does not make sense in the host application.
• Two strings can not be concatenated using the + operator; instead the + operator will convert the strings to numbers and sum them. Use the @ operator for string concatenation (this is a libfawk-specific feature that is present in all libfawk scripting languages).
• Arrays are indexed using the [] brackets, not () parenthesis; reason: function reference can be saved in arrays.
• There is no DIM and REDIM: arrays are created automatically upon first reference with [].
• There is no GOSUB, RETURN, because they are incompatible with libfawk functions
• Labels (and line numbers) are function-local; that means the same label (or line number) can appear in multiple different functions and in the main program (but only once in each function or program) and will still mean a different thing. This also means GOTO can not be used to do a cross-function jump as it can not address labels of a different function.
• A single line number without the goto keyword in an if-then will NOT be a goto.
• Single line if-then is accepted, but if-then-else always needs to be multi-line, with an end if terminator. There is no support for elseif.
• There is no DATA, READ and RESTORE. Just use arrays, they are powerful in this dialect.
• $ suffix in variable names are allowed but makes no difference in variable type (i.e. strings don't require $ and $ won't force the variable to be a string)
• there is no "exit for" or "exit do"; use goto to break loops
• there is support for variable argument (vararg) functions
• text-block support: multiline template-like string "literal" type with expression inserts

Rationale

Why bracketed arrays?

Consider A[1](2). It clearly means A is an array, A[1] is a member of the array referencing a function and (2) is the call parameter. If it was A(1)(2), it could also be interpreted as an array-in-array situation (equivalent to A[1][2] in the current syntax).

Why no gosub?

Soft reason: size vs. features. Gosub does not make it possible to pass function parameters while the alternative syntax with def/function does. To keep the code small, only one syntax is implemented for the same feature, which is def/function in this case.

Hard reason: the libfawk VM and the host application expects to call a function called main() within the script. With BASIC this is not the case since the main program just starts outside of functions. To make this possible, there is a trick in the compiler - a trick that needs to know the start of each function, which is not possible with subroutines defined for gosub.