2.13. Block

Blocks are nameless functions which captures the local context by reference. Blocks offer significant performance advantages over lambdas (see Lambda).

The block type can be declared with a function-like syntax:

block_type ::= block { optional_block_type }
optional_block_type ::= < { optional_block_arguments } { : return_type } >
optional_block_arguments := ( block_argument_list )
block_argument_list := argument_name : type | block_argument_list ; argument_name : type

block < (arg1:int;arg2:float&):bool >

Blocks capture the current stack, so blocks can be passed, but never returned. Block variables can only be passed as arguments. Global or local block variables are prohibited; returning the block type is also prohibited:

def goo ( b : block )
    ...

def foo ( b : block < (arg1:int; arg2:float&) : bool >
    ...

Blocks can be called via invoke:

def radd(var ext:int&;b:block<(var arg:int&):int>):int
    return invoke(b,ext)

Typeless blocks are typically declared via pipe syntax:

goo() <|                                // block without arguments
    print("inside goo")

Similarly typed blocks are typically declared via pipe syntax:

var v1 = 1                              // block with arguments
res = radd(v1) <| $(var a:int&):int
    return a++

Blocks can also be declared via inline syntax:

res = radd(v1, $(var a:int&) : int { return a++; }) // equivalent to example above

There is a simplified syntax for blocks that only contain a return expression:

res = radd(v1, $(var a:int&) : int => a++ )         // equivalent to example above

If a block is sufficiently specified in the generic or function, block types will be automatically inferred:

res = radd(v1, $(a) => a++ )                        // equivalent to example above

Nested blocks are allowed:

def passthroughFoo(a:Foo; blk:block<(b:Foo):void>)
    invoke(blk,a)

passthrough(1) <| $ ( a )
    assert(a==1)
    passthrough(2) <| $ ( b )
        assert(a==1 && b==2)
        passthrough(3) <| $ ( c )
            assert(a==1 && b==2 && c==3)

Loop control expressions are not allowed to cross block boundaries:

while true
    take_any() <|
        break               // 30801, captured block can't break outside the block

Blocks can have annotations:

def queryOne(dt:float=1.0f)
    testProfile::queryEs() <| $ [es] (var pos:float3&;vel:float3 const)  // [es] is annotation
        pos += vel * dt

Block annotations can be implemented via appropriate macros (see Macro).