conditional.md

Conditional

Basically if in most languages

C if example.

    if(true){
        x = 1
    }else{
        x = 0
    }

SI

    x = @when true, { 1 } , { 0 };
    x = @when true, 1, 0;
    @when true, (@fn_ true = { x = 1 } , @fn_ false = { x = 0 })

NEW

    @let x = &@if true, 1, 0;

    @fn if true, then, _= &then;
    @fn if false, _, else = &else;

When

Silicon doesn't have a direct equivalent to if. Instead, it has a more powerful and versatile @when, which is closer to match in ML languages.

Silicon only has functions even @when in just a built-in function.

IF

Silicon doesn't have an if in the traditional sense. It really isn't needed since we have pattern matching with functions. We can define an anonymous function

```silicon
    @fn_ $true = {
        // then
    }
    @fn_ $false = {
        // else
    }
```

With potential lambda syntax

```silicon
    \$true = {
        // then
    }

    \$false = {
        // else
    }
```

The convention is to keep the whole function definition together in parenthesis. The Sigil LSP will give a warning: function pattern matching definitions aren't grouped together. See [link]()

```silicon
    (\$true = {
        // then
    },
    \$false = {
        // else
    })
```

Idea

// technically a @when for pattern matching isn't needed either. With pipe syntax, it is really clean to define an inline function that we pass the data to. @when will likely exist but be renamed since effectively it is just apply.

Silicon core (the initial)

    @loop ,1..30, @fn _,n = {
        (n, n.factorOf(3), n.factorOf(5)) |> (@fn_ n, true, false = {
            #print "fizz"
        })
     }

IF

Silicon has a cool syntax, almost like a DSL for function parameters. Using the atom sigil, $.

    @if true
    $then { x = 1 }
    $else { x = 0 };

You may notice the code is always in {}. Silicon is consistent. {} denote reusable code blocks. Without them that would just be static code. So unlike ML languages @func add a,b = a + b won't work because a and b refer to parent scope not the block scope. @func add a,b = { a + b }. Slightly less verbose.

@when is a function with three parameters: condition, then_block, else_block. The else_block is optional of course.

Here is how If is defined in the compiler.

@name if true, then_block, _ = #then_block;
@name if false, _ , null  = #NOP; // if else block isn't defined, no nothing (no op method)
@name if false, _ , else_block = #else_block;