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add short section on global variables

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Dennis Ranke
2022-01-09 22:09:59 +01:00
parent e58b13c8ee
commit ce8435e3dc
1 changed files with 19 additions and 5 deletions
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README.md
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@@ -58,7 +58,7 @@ Then run it on [MicroW8](https://exoticorn.github.io/microw8/v0.1pre2)
### Types
There are four types in WebAssembly and therefore Curlywas:
There are four types in WebAssembly and therefore CurlyWas:
* `i32`: 32bit integer
* `i64`: 64bit integer
@@ -93,7 +93,7 @@ this does not work, yet:
### Imports
WebAssembly imports are specified with a module and a name. In Curlywas you give them inside a single string literal, seperated by a dot. So a module `env` and name `printString` would be written `"env.printString"`.
WebAssembly imports are specified with a module and a name. In CurlyWas you give them inside a single string literal, seperated by a dot. So a module `env` and name `printString` would be written `"env.printString"`.
Linear memory can be imported like this:
@@ -124,6 +124,20 @@ import "env.random" rand() -> i32; // no params
import "env.atan2" atan2(f32, f32) -> f32;
```
### Global variables
Global variables are declare like this:
```
global name[: type] = value; // immutable global value
global mut name[: type] = initial_value; // mutable variable
```
An immutable global is probably of very limited use, as usually you'd most often use it by exporting it so that some other module
can use it. However, exporting global variable is not yet supported in CurlyWas.
The type is optional, if missing it is inferred from the init value.
### Functions
Functions look like this:
@@ -298,7 +312,7 @@ Sometimes when sizeoptimizing it helps to be able to execute some side-effecty c
Using a block scope, we can execute any number of statements before evaluating a final expression to an actual value. For example:
```
let x = { randomSeed(time); random() }; // set the random seed right before optaining a random value
let x = { randomSeed(time); random() }; // set the random seed right before obtaining a random value
```
To execute something after evaluating the value we want to return, we can use the `<|` operator. Here is an example from the Wasm4 version of
@@ -319,11 +333,11 @@ after drawing a rectangle with color `c` and setting the color for the text to `
## Limitations
The idea of Curlywas is to be able to hand-craft any valid WASM program, ie. having the same amount of control over the instruction sequence as if you would write in the web assembly text format (`.wat`) just with better ergonomics.
The idea of CurlyWas is to be able to hand-craft any valid WASM program, ie. having the same amount of control over the instruction sequence as if you would write in the web assembly text format (`.wat`) just with better ergonomics.
This goal is not yet fully reached, with the following being the main limitations:
* Curlywas currently only targets MVP web assembly + non-trapping float-to-int conversions. No other post-MVP features are currently supported. Especially "Multi-value" will be problematic as this allows programs that don't map cleanly to an expression tree.
* CurlyWas currently only targets MVP web assembly + non-trapping float-to-int conversions. No other post-MVP features are currently supported. Especially "Multi-value" will be problematic as this allows programs that don't map cleanly to an expression tree.
* Memory intrinsics are still missing, so only (unsigned) 8 and 32 bit integer reads and writes are possible.
* `block`s cannot return values, as the branch instructions are missing syntax to pass along a value.
* `br_table` and `call_indirect` are not yet implemented.