language

The MVX BASIC Language

Programs and subroutines

A main program is a sequence of statements; execution starts at the top and ends at END, STOP, or falling off the end. A subroutine begins with a SUBROUTINE declaration and returns with RETURN:

SUBROUTINE GREET(NAME, RESULT)
RESULT = "hello ":NAME
RETURN

Arguments pass by reference: the callee can change the caller's variables. Subroutines compile separately (into shared libraries when cataloged) and are resolved at CALL time.

Lines, labels and comments

One statement per line; ; separates multiple statements on a line. A number at the start of a line is a statement label for GOTO and GOSUB.

Comments come in classic and C styles:

* classic full-line comment
! also classic
REM likewise
X = 1 ; * classic trailing comment
// C-style line comment
Y = 2 /* inline block */ + 3
/**
 * Block comments span lines - the usual home of docblocks.
 * @file MYPROG
 * @version 1.0
 */

C-style comments are an MVX extension. They cannot be confused with division (/ must be followed by an operand in valid code), and newlines inside a block comment still end statements. The PORT-SOURCE verb rewrites them as classic comments for legacy platforms.

Values

A variable holds a dynamic string that may also be a number. Numbers never round-trip through text internally: arithmetic on numeric values is native, and the compiler specialises provably numeric variables and arrays down to machine integers and doubles. None of that changes semantics — it is why MVX is fast.

String comparison follows MV rules: if both operands look numeric, they compare numerically; otherwise byte-wise. An unassigned variable warns once and reads as zero / empty.

Literals: 123, 12.5, "text", 'text'.

Operators

arithmetic	+ - * / ^ (power)
string	: concatenation
comparison	= # < > <= >= (also EQ NE LT GT LE GE)
logic	AND OR NOT(x)
substring	X[start, len] (1-based)
format	X "R#10" — apply a format mask (also FMT(X, mask))

Dynamic arrays

The heart of MV data. A dynamic array is a string with attribute (@AM), value (@VM) and subvalue (@SM) marks:

REC = "Widget":@AM:"9.99":@AM:"blue"
PRINT REC<2>              -> 9.99
REC<2> = "10.50"          replace attribute 2
REC<-1> = "new"           append an attribute
V = REC<1,2>              value 2 within attribute 1

Angle-bracket extraction and replacement work at all three levels and pad with marks when writing past the end. The function forms EXTRACT, REPLACE, INSERT, and DELETE do the same work on copies. LOCATE searches a level, optionally maintaining sort order — the classic idiom for both membership tests and ordered insertion.

Dimensioned arrays

DIM A(10) or DIM T(5, 4): fixed-size, 1-based, bounds-checked. MAT A = 0 fills; MAT A = MAT B copies. Dimensioned arrays are distinct from dynamic arrays and compile to flat native storage when their contents are provably numeric.

COMMON

COMMON A, B, ARR(10) declares variables shared positionally between a main program and everything it CALLs; COMMON /NAME/ ... names a block. COMMON storage lives in the session, so separately compiled subroutines see the same data.