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tutorial update
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@robertmuth
robertmuth committed Jun 24, 2024
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* limited polymorphism
* slices (array views)
* (almost) no implicit conversions
* no truthinesss
* all value are zero initialized by default

## Examples

Cwerg use a Python inspired syntax where the indentation level
is significant.

We give some examples below to convey a general feeling for the language.
The details should become clear after reading through the tutorial.

### Hello World (full example)

```
Expand Down Expand Up @@ -66,13 +70,14 @@ The `@pub` annotation makes `fib` visible outside of the module.
-- a global constant
global N uint = 1000 * 1000 * 1000;
-- a mutable global array of bool initialized to `true`
-- a mutable global array of bools initialized to `true`
-- index i reprents number 3 + 2 * i
global! is_prime = [N]bool{true}
-- Count the number of primes below n
fun sieve() uint:
let! count uint = 1
-- the type of `i` is determined by `N`
for i = 0, N, 1:
if is_prime[i]:
set count += 1
Expand All @@ -84,7 +89,47 @@ fun sieve() uint:

Exclamtion marks at the end of keywords indicate mutability.

##
## Binary Tree (parameterized/generic module)

```
module BinaryTree(
-- the payload type
$type TYPE,
-- the less-than function ($type x $type) -> bool
$lt CONST_EXPR):
@pub global Leaf = void
@pub rec Node:
left union(void, ^!Node)
right union(void, ^!Node)
payload $type
-- same as above for left and right
@pub type MaybeNode = union(void, ^!Node)
type Visitor = funtype(node ^$type) void
@pub fun InorderTraversal(root MaybeNode, visitor Visitor) void:
trylet node ^!Node = root, _:
return
do InorderTraversal(node^.left, visitor)
do visitor(&node^.payload)
do InorderTraversal(node^.right, visitor)
-- returns the new root
@pub fun Insert(root MaybeNode, node ^!Node) ^!Node:
set node^.left = Leaf
set node^.right = Leaf
trylet curr ^!Node = root, _:
return node
if $lt(&node^.payload, &curr^.payload):
set curr^.left = Insert(curr^.left, node)
else:
set curr^.right = Insert(curr^.right, node)
return curr
```

## Type System

Expand All @@ -95,7 +140,7 @@ Cwerg's type system is similar to C's with the following differences
* there is a stronger emphasis on "const/mutability correctness"
* arrays do not decay to to pointers and arrays of different sizes
are different types
* slices can be used where arrays like objects with variable length are required
* slices can be used where array-like objects with variable length are required
* (tagged) unions are supported to simplifying error handling and emulate nullable
pointers

Expand All @@ -113,6 +158,7 @@ Cwerg's type system is similar to C's with the following differences
### Pointer Types

The pointer type notation is similar to Pascal.
The caret goes in front of type.

```
-- pointer to a u32
Expand All @@ -124,12 +170,19 @@ The pointer type notation is similar to Pascal.

### Arrays

Array of different length are not compatible
Array dimension go in front of the element type:

```
-- 10 element array of element type u32
[10]u32
[10]u32
```

Array of different length are not compatible and
are different from pointers to the element type.
```
static_assert typeidof([10]u32) != typeidof([2]u32)
static_assert typeidof([10]u32) != typeidof(^u32)
```

### Slices
Expand All @@ -149,7 +202,7 @@ slice!(u32)

Function type can be described like so:
```
funtype(param1 type1, param2 type2, ...) return-type
funtype(param1 type1, param2 type2, ...) return-type
```
### Records

Expand Down Expand Up @@ -183,7 +236,7 @@ enum Color u8:

This declares an enum `Color` with 3 members (`red`, `green`, `blue`)
with an underlying type of `u8`.
`auto` is used the previously asigned value incremented by 1 or zero if it is the first member. So in the above example we get:
`auto` is using the previously asigned value incremented by 1 or zero if it is the first member. So in the above example we get:
```
Color:blue has value 0
Color:green has value 10
Expand All @@ -202,7 +255,7 @@ type t1 = funtype(x u8, y u8) u1
```


This is strictly and abbreviation, the lhs and the rhs can be used interchangably in the code.
This is strictly an abbreviation, the lhs and the rhs can be used interchangably in the code.

To force by name type equivalence in this case, use the `@wrapped` annotation like so
```
Expand All @@ -215,22 +268,23 @@ The type `t1` is said to be a wrapped type.
### (Tagged) Unions


Tagged unions can be declared liek so:
Tagged unions can be declared like so:

```
union(s32, void, u8, ^sint, [32]u8))
```

Note, that there are no names only types. In case that the same type is
needed twice in a single union, wrapped types can be used.
Note, that there are no names - only types. In case that the same type is
needed twice in a single union, wrapped types can be used.

The annotation `@untagged` changes a union to untagged.

Unions are a order independent, duplicate eliminating, and auto-flattening.
Unions are: order independent, duplicate eliminating, and auto-flattening.
In the example below `u1` and `u2` are the same type:
```
type u1 = union (u8, s64, union(u8, s32), union(u8, void))
type u2 = union (s64, s32, void, u8))
static_assert typeidof)u1) == typeidof)u2)
```

More info in [Unions](union_types.md)
Expand All @@ -243,7 +297,7 @@ More info in [Unions](union_types.md)

`true`, `false`

There is no concept of truthiness
There is no concept of truthiness.

### String Literals

Expand Down Expand Up @@ -427,7 +481,7 @@ Controlflow will resume at the next statement after block if
the control flow falls throuh the last statement of the block.
```
block <NAME>?:
<STAREMENTS>+
<STAREMENTS>*
```

A `continue` statement inside the block will set controlflow to the beginning
Expand All @@ -439,15 +493,15 @@ which enclosing `block` they refer to.

```
while <CONDITION>:
<STAREMENTS>+
<STAREMENTS>*
```


### For Loops

```
for var-name = initial-expr, limit-expr, step-expr:
<STAREMENTS>+
<STAREMENTS>*
```

For loops differ from their C counterparts in the following way:
Expand All @@ -460,29 +514,42 @@ a macro.

### If-else Statements

Simple
```
if condition:
<STAREMENTS>*
```

With else clause

```
if condition:
<STAREMENTS>+
<STAREMENTS>*
else:
<STAREMENTS>+
<STAREMENTS>*
```

### Cond Statements

```
cond:
case condition1:
<STAREMENTS>+
<STAREMENTS>*
case condition2:
<STAREMENTS>+
<STAREMENTS>*
...
```

Note, there is no fallthrough.
Case are checked in order.
A `default` case be expressed as `case true`
and must go last.

### Defer Statements

```
defer:
<STAREMENTS>+
<STAREMENTS>*
```

The code in the defer body will be run when the enclosing scope is exited.
Expand Down Expand Up @@ -535,10 +602,6 @@ do expression
Runs the expression and discards the result






## Expressions

### Prefix Operators
Expand Down Expand Up @@ -600,7 +663,7 @@ Note, operator precendence has yet to be finalized
| stringify(E) -> []u8 | convert an expression to a textual representation |


Casts
### Casts


TBD - see [Casting](casting.md)
Expand Down

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