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