Shortcomings (that I know about)

• Extremely fragile interpreter. I didn't even try to make this robust, so malformed BASIC will most likely mimic g++ error messages.
• Order of operations simply does not exist. To get correct math evaluation, use a copious amount of parentheses: 2 + 3 * 2 incorrectly evaluates to 8, but 2 * (3 + 2) correctly produces 10.
• Very limited feature set. The goal was to produce a minimal functional BASIC interpreter for use on the Pi Pico.
• Unary negation is beyond my comprehension for some reason, so if you want negative literals, do (0 - number): -5 == (0 - 5)

Keyword reference

Keyword	Syntax	Description
PRINT	PRINT (expr)	Evaluate the expression and print it
PRINTNL	PRINTNL (expr)	Same as print but without adding a newline
INPUT	INPUT (ident)	Read a single character from input and store into ident
LET	N/A	Tokenized but not used (ignored).
IF	IF (expr) THEN (expr)	If the expression evaluates to 1 (True), jump to the line evaluated by the second expr.
THEN	N/A	Part of IF
FOR	FOR (ident) = (expr) TO (expr) [STEP (expr)]	Set the ident to first expr, loop until end expr, optionally step by final expr per loop.
TO	N/A	Part of FOR, PEEK, and POKE
STEP	N/A	Part of FOR
GOTO	GOTO (expr)	Jump to line evaluated by expr
PEEK	PEEK (expr) TO (ident)	Store the value in memory at expr into ident
POKE	POKE (ident) TO (expr)	Store the value of ident in memory at expr
GOSUB	N/A	Tokenized but not used (ignored).
RETURN	N/A	Tokenized but not used (ignored).
END	END	Terminates interpretation immediately
REM	REM ...	Remarks are completely ignored

Variables

All variables are either a number, string, or array. Variables are case-sensitive, i.e. "X" is not the same as "x". Variables are not strongly typed, so their type can be re-assigned:

10REM "X will be the string Hello"20 X ="Hello"30REM "X will be re-assigned to a number (the length of the string it previously held, 5)"40 X =LEN(X)

Arrays

Arrays can be defined with the ARRAY(number) function. The length of the array is the number provided to the function. Arrays cannot grow/shrink, but adding two arrays will concatenate them into a single larger array:

10REM "X is an array with 5 elements (all initialized to 0)"20 X = ARRAY(5)
30REM "Arrays cannot be resized once created, but adding two together creates a new larger array:"40 Y = X + ARRAY(15)
50REM "Y is an array with space for 20 elements (5 from X, 15 from the anonymous array)"60PRINT"Y has room for ", LEN(Y), " elements."70REM "Arrays can hold any type in each element, including themselves:"80 Y[0] = Y
90PRINT Y[0][0][0]

Functions

Function	Argument type	Return type	Description
ABS	number	number	Absolute value of number
LEN	string or array	number	Length of argument
CHR	number	string	Number to ASCII
INT	string	number	Convert first character of string to number
PEEK	number	any	Same as PEEK keyword
LCASE	string	string	Convert string to lowercase
UCASE	string	string	Convert string to uppercase
ARRAY	number	array	Return an empty array of specified length
TYPE	any	string	Return type name of argument ("number", "string", "array")
SIN	number	number	sine(number)
COS	number	number	cosine(number)
TAN	number	number	tangent(number)
SQRT	number	number	square root(number)
LOG	number	number	log base 10
FLOOR	number	number	Round down number to nearest integer
CEIL	number	number	Round up number to nearest integer
DEG	number	number	Convert radians to degrees
RAD	number	number	Convert degrees to radians
ISNAN	number	number (0 or 1)	Check if number is NaN
ISINF	number	number (0 or 1)	Check if number is ±Inf

Operators

Operator	Argument types	Return type	Description
+	number or array	number or array	numbers: addition; arrays: concatenation
-	number	number	subtraction
/	number	number	division
^	number	number	exponentiation
%	number	number	modulo
=	any	none	assignment
!	N/A	N/A	not used
<	number	number (0 or 1)	less than
<=	number	number (0 or 1)	less than or equal
>	number	number (0 or 1)	greater than
>=	number	number (0 or 1)	greater than or equal
==	number or string	number (0 or 1)	equals
!=	number or string	number (0 or 1)	not equals
,	any	string	string coercion and concatenation
( and )	any	any	evaluation grouping, function calls
[ and ]	array	any	array indexing