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finish first rough version of syntax docs

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Dennis Ranke
2022-01-08 22:32:41 +01:00
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README.md
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@@ -144,6 +144,8 @@ export fn upd() {
} }
``` ```
The body of a function is a block (see below), meaning a sequence of statements followed by an optional expression which gives the return value of the function.
#### Local variables #### Local variables
Variables are defined using `let`: Variables are defined using `let`:
@@ -280,7 +282,15 @@ non-zero integer.
#### Memory load/store #### Memory load/store
... To read from memory you specify a memory location as `base?offset` or `base!offset`. `?` reads a byte and `!` reads a 32bit word.
`base` can be any expression that evaluates to an `i32` while `offset` has to be a constant `i32` value. The effective memory address is the sum of both.
Writing to memory looks just like an assignment to a memory location: `base?offset = expressoin` and `base!offset = expression`.
When reading/writing 32bit words you need to make sure the address is 4-byte aligned.
These compile to `i32.load8_u`, `i32.load`, `i32.store8` and `i32.store`. Other WASM load/store instructions will be implemented as intrinsics, but aren't yet.
#### Advanced sequencing #### Advanced sequencing
@@ -306,3 +316,14 @@ after drawing a rectangle with color `c` and setting the color for the text to `
* Call `rect` which draws a rectangle with the set color. This call doesn't affect the stack. * Call `rect` which draws a rectangle with the set color. This call doesn't affect the stack.
* Call `set_color(4)` which sets the drawing color to `4` and pushes another 6 on the stack. * Call `set_color(4)` which sets the drawing color to `4` and pushes another 6 on the stack.
* Call `text` with the parameters (`8000`, `6`, `6`) pushed on the stack. * Call `text` with the parameters (`8000`, `6`, `6`) pushed on the stack.
## 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.
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.
* 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.