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Put app-common documentation in apps/README.md
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@ -61,3 +61,38 @@ relevant parts of the app's glue unit in your kernel's glue unit. This is often
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simpler and more efficient. However, if your shell is a big program, it might
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simpler and more efficient. However, if your shell is a big program, it might
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run into zasm's limits. In that case, you'd have to assemble your shell
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run into zasm's limits. In that case, you'd have to assemble your shell
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separately.
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separately.
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## Common features
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The folder `lib/` contains code shared in more than one apps and this has the
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effect that some concepts are exactly the same in many application. They are
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therefore sharing documentation, here.
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### Number literals
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There are decimal, hexadecimal and binary literals. A "straight" number is
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parsed as a decimal. Hexadecimal literals must be prefixed with `0x` (`0xf4`).
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Binary must be prefixed with `0b` (`0b01100110`).
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Decimals and hexadecimal are "flexible". Whether they're written in a byte or
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a word, you don't need to prefix them with zeroes. Watch out for overflow,
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however.
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Binary literals are also "flexible" (`0b110` is fine), but can't go over a byte.
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There is also the char literal (`'X'`), that is, two quotes with a character in
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the middle. The value of that character is interpreted as-is, without any
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encoding involved. That is, whatever binary code is written in between those
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two quotes, it's what is evaluated. Only a single byte at once can be evaluated
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thus. There is no escaping. `'''` results in `0x27`. You can't express a newline
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this way, it's going to mess with the parser.
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### Expressions
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An expression is a bunch of literals or symbols assembled by operators. For
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now, only `+`, `-` and `*` operators are supported. No parenthesis yet.
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Symbols have a different meaning depending on the application. In zasm, it's
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labels and constants. In basic, it's variables.
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Expressions can't contain spaces.
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@ -49,12 +49,11 @@ by typing a whitespace.
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Only 16-bit integers (unsigned for now) are supported in this BASIC. When
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Only 16-bit integers (unsigned for now) are supported in this BASIC. When
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printed, they're printed in decimal form. When expressing number literals, you
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printed, they're printed in decimal form. When expressing number literals, you
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can do so either in decimal (`42`), hexadecimal (`0x2a`), binary (`0b101010`)
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can do so either in multiple forms. . See "Number literals" in `apps/README.md`
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or char ('a', resulting in number 97).
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for details.
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Expressions are accepted wherever a number is expected. For example,
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Expressions are accepted wherever a number is expected. For example,
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`print 2+3` will print `5`. Expressions can't have whitespace inside them and
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`print 2+3` will print `5`. See "Expressions" in `apps/README.md`.
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don't support (yet) parentheses. Supported operators are `+`, `-`, `*` and `/`.
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Inside a `if` command, "truth" expressions are accepted (`=`, `<`, `>`, `<=`,
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Inside a `if` command, "truth" expressions are accepted (`=`, `<`, `>`, `<=`,
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`>=`). A thruth expression that doesn't contain a truth operator evaluates the
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`>=`). A thruth expression that doesn't contain a truth operator evaluates the
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@ -28,28 +28,13 @@ The resulting `zasm` binary takes asm code in stdin and spits binary in stdout.
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## Literals
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## Literals
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There are decimal, hexadecimal and binary literals. A "straight" number is
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See "Number literals" in `apps/README.md`.
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parsed as a decimal. Hexadecimal literals must be prefixed with `0x` (`0xf4`).
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Binary must be prefixed with `0b` (`0b01100110`).
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Decimals and hexadecimal are "flexible". Whether they're written in a byte or
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On top of common literal logic, zasm also has string literals. It's a chain of
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a word, you don't need to prefix them with zeroes. Watch out for overflow,
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characters surrounded by double quotes. Example: `"foo"`. This literal can only
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however.
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be used in the `.db` directive and is equivalent to each character being
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single-quoted and separated by commas (`'f', 'o', 'o'`). No null char is
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Binary literals are also "flexible" (`0b110` is fine), but can't go over a byte.
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inserted in the resulting value (unlike what C does).
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There is also the char literal (`'X'`), that is, two qutes with a character in
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the middle. The value of that character is interpreted as-is, without any
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encoding involved. That is, whatever binary code is written in between those
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two quotes, it's what is evaluated. Only a single byte at once can be evaluated
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thus. There is no escaping. `'''` results in `0x27`. You can't express a newline
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this way, it's going to mess with the parser.
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Then comes our last literal, the string literal. It's a chain of characters
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surrounded by double quotes. Example: `"foo"`. This literal can only be used
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in the `.db` directive and is equivalent to each character being single-quoted
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and separated by commas (`'f', 'o', 'o'`). No null char is inserted in the
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resulting value (unlike what C does).
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## Labels
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## Labels
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@ -100,11 +85,7 @@ of declaration order.
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## Expressions
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## Expressions
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Wherever a constant is expected, an expression can be written. An expression
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See "Expressions" in `apps/README.md`.
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is a bunch of literals or symbols assembled by operators. For now, only `+`, `-`
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and `*` operators are supported. No parenthesis yet.
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Expressions can't contain spaces.
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## The Program Counter
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## The Program Counter
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