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Put app-common documentation in apps/README.md

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Virgil Dupras 2019-11-22 14:01:16 -05:00
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35
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
simpler and more efficient. However, if your shell is a big program, it might
run into zasm's limits. In that case, you'd have to assemble your shell
separately.
## Common features
The folder `lib/` contains code shared in more than one apps and this has the
effect that some concepts are exactly the same in many application. They are
therefore sharing documentation, here.
### Number literals
There are decimal, hexadecimal and binary literals. A "straight" number is
parsed as a decimal. Hexadecimal literals must be prefixed with `0x` (`0xf4`).
Binary must be prefixed with `0b` (`0b01100110`).
Decimals and hexadecimal are "flexible". Whether they're written in a byte or
a word, you don't need to prefix them with zeroes. Watch out for overflow,
however.
Binary literals are also "flexible" (`0b110` is fine), but can't go over a byte.
There is also the char literal (`'X'`), that is, two quotes with a character in
the middle. The value of that character is interpreted as-is, without any
encoding involved. That is, whatever binary code is written in between those
two quotes, it's what is evaluated. Only a single byte at once can be evaluated
thus. There is no escaping. `'''` results in `0x27`. You can't express a newline
this way, it's going to mess with the parser.
### Expressions
An expression is a bunch of literals or symbols assembled by operators. For
now, only `+`, `-` and `*` operators are supported. No parenthesis yet.
Symbols have a different meaning depending on the application. In zasm, it's
labels and constants. In basic, it's variables.
Expressions can't contain spaces.

7
apps/basic/README.md
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@ -49,12 +49,11 @@ by typing a whitespace.
Only 16-bit integers (unsigned for now) are supported in this BASIC. When
printed, they're printed in decimal form. When expressing number literals, you
can do so either in decimal (`42`), hexadecimal (`0x2a`), binary (`0b101010`)
or char ('a', resulting in number 97).
can do so either in multiple forms. . See "Number literals" in `apps/README.md`
for details.
Expressions are accepted wherever a number is expected. For example,
`print 2+3` will print `5`. Expressions can't have whitespace inside them and
don't support (yet) parentheses. Supported operators are `+`, `-`, `*` and `/`.
`print 2+3` will print `5`. See "Expressions" in `apps/README.md`.
Inside a `if` command, "truth" expressions are accepted (`=`, `<`, `>`, `<=`,
`>=`). A thruth expression that doesn't contain a truth operator evaluates the

33
apps/zasm/README.md
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@ -28,28 +28,13 @@ The resulting `zasm` binary takes asm code in stdin and spits binary in stdout.
## Literals
There are decimal, hexadecimal and binary literals. A "straight" number is
parsed as a decimal. Hexadecimal literals must be prefixed with `0x` (`0xf4`).
Binary must be prefixed with `0b` (`0b01100110`).
See "Number literals" in `apps/README.md`.
Decimals and hexadecimal are "flexible". Whether they're written in a byte or
a word, you don't need to prefix them with zeroes. Watch out for overflow,
however.
Binary literals are also "flexible" (`0b110` is fine), but can't go over a byte.
There is also the char literal (`'X'`), that is, two qutes with a character in
the middle. The value of that character is interpreted as-is, without any
encoding involved. That is, whatever binary code is written in between those
two quotes, it's what is evaluated. Only a single byte at once can be evaluated
thus. There is no escaping. `'''` results in `0x27`. You can't express a newline
this way, it's going to mess with the parser.
Then comes our last literal, the string literal. It's a chain of characters
surrounded by double quotes. Example: `"foo"`. This literal can only be used
in the `.db` directive and is equivalent to each character being single-quoted
and separated by commas (`'f', 'o', 'o'`). No null char is inserted in the
resulting value (unlike what C does).
On top of common literal logic, zasm also has string literals. It's a chain of
characters surrounded by double quotes. Example: `"foo"`. This literal can only
be used in the `.db` directive and is equivalent to each character being
single-quoted and separated by commas (`'f', 'o', 'o'`). No null char is
inserted in the resulting value (unlike what C does).
## Labels
@ -100,11 +85,7 @@ of declaration order.
## Expressions
Wherever a constant is expected, an expression can be written. An expression
is a bunch of literals or symbols assembled by operators. For now, only `+`, `-`
and `*` operators are supported. No parenthesis yet.
Expressions can't contain spaces.
See "Expressions" in `apps/README.md`.
## The Program Counter