2018-01-04 00:15:04 +00:00
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# Syntax
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2018-01-18 21:35:25 +00:00
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For information about types, see [Types](./types.md).
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For information about literals, see [Literals](./literals.md).
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For information about assembly, see [Using assembly within Millfork programs](./assembly.md).
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## Comments
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Comments start with `//` and last until the end of line.
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## Declarations
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### Variable declarations
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A variable declaration can happen at either top level of a file (*global* variables),
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or a top level of a function (*local* variables).
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Syntax:
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`[<storage>] <type> <name> [@<address>] [= <initial_value>]`
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2018-02-01 21:39:38 +00:00
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* `<storage>` can be only specified for local variables. It can be either `stack`, `static`, `register` or nothing.
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`register` is only a hint for the optimizer.
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2018-01-18 21:35:25 +00:00
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See [the description of variable storage](../abi/variable-storage.md).
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* `<address>` is a constant expression that defines where in the memory the variable will be located.
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If not specified, it will be located according to the usual allocation rules.
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`stack` variables cannot have a defined address.
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* `<initial_value>` is a constant expression that contains the initial value of the variable.
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Only global variables can be initialized that way.
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The behaviour is undefined when targeting a ROM-based platform.
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### Constant declarations
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`const <type> <name> = <value>`
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TODO
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### Array declarations
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An array is a continuous sequence of bytes in memory.
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Syntax:
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`array <name> [[<size>]] [@<address>] [= <initial_values>]`
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TODO
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### Function declarations
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A function can be declared at the top level. For more details, see [Functions](./functions.md)
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## `import` statements
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TODO
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## Statements
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### Expression statement
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TODO
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### `if` statement
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Syntax:
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```
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if <expression> {
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<body>
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}
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```
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```
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if <expression> {
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<body>
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} else {
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<body>
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}
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```
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2018-01-30 16:38:32 +00:00
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### `return` statement
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Syntax:
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```
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return
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```
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```
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return <expression>
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```
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### `return[]` statement (return dispatch)
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Syntax examples:
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```
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return [a + b] {
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0 @ underflow
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255 @ overflow
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default @ nothing
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}
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```
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```
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return [getF()] {
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1 @ function1
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2 @ function2
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default(5) @ functionDefault
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}
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```
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```
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return [i] (param1, param2) {
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1,5,8 @ function1(4, 6)
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2 @ function2(9)
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default(0,20) @ functionDefault
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}
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```
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Return dispatch calculates the value of an index, picks the correct branch,
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assigns some global variables and jumps to another function.
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2018-02-01 21:39:38 +00:00
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The index has to evaluate to a byte. The functions cannot be `macro` and shouldn't have parameters.
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2018-01-30 16:38:32 +00:00
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Jumping to a function with parameters gives those parameters undefined values.
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The functions are not called, so they don't return to the function the return dispatch statement is in, but to its caller.
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The return values are passed along. If the dispatching function has a non-`void` return type different that the type
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of the function dispatched to, the return value is undefined.
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If the `default` branch exists, then it is used for every missing index value between other supported values.
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Optional parameters to `default` specify the maximum, or both the minimum and maximum supported index value.
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In the above examples: the first example supports values 0–255, second 1–5, and third 0–20.
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If the index has an unsupported value, the behaviour is formally undefined, but in practice the program will simply crash.
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Before jumping to the function, the chosen global variables will be assigned parameter values.
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Variables have to be global byte-sized. Some simple array indexing expressions are also allowed.
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Parameter values have to be constants.
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For example, in the third example one of the following will happen:
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* if `i` is 1, 5 or 8, then `param1` is assigned 4, `param2` is assigned 6 and then `function1` is called;
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* if `i` is 2, then `param1` is assigned 9, `param2` is assigned an undefined value and then `function2` is called;
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* if `i` is any other value from 0 to 20, then `param1` and `param2` are assigned undefined values and then `functionDefault` is called;
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* if `i` has any other value, then undefined behaviour.
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2018-01-18 21:35:25 +00:00
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### `while` and `do-while` statements
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Syntax:
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```
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while <expression> {
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<body>
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}
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```
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```
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do {
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<body>
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} while <expression>
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```
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### `for` statements
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**Warning: `for` loops are a bit buggy.**
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Syntax:
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```
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for <variable>,<start>,<direction>,<end> {
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}
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```
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* `<variable>` – an already defined numeric variable
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* `<direction>` – the range to traverse:
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* `to` – from `<start>` inclusive to `<end>` inclusive, in ascending order
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(e.g. `0,to,9` to traverse 0, 1,... 9)
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* `downto` – from `<start>` inclusive to `<end>` inclusive, in descending order
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(e.g. `9,downto,0` to traverse 9, 8,... 0)
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* `until` – from `<start>` inclusive to `<end>` exclusive, in ascending order
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(e.g. `0,until,10` to traverse 0, 1,... 9)
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* `parallelto` – the same as `to`, but the iterations may be executed in any order
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* `paralleluntil` – the same as `until`, but the iterations may be executed in any order
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There is no `paralleldownto`, because it would do the same as `parallelto`.
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### `asm` statements
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See [Using assembly within Millfork programs](./assembly.md).
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