Well, the example above is low level. For convenience lua.cr is designed to be more high level. The API I am thinking about is the following:

lua = Lua.load

# define a new crystal callback/function
lua.function "crystal_add" do |x, y|
  x + y
end

# use it in Lua
lua.eval %q{
  return 100 * crystal_add(3, 4)
} #=> 700.0

Here is the same that is written in a low-level manner:

lua = Lua.load

proc = ->(state : LibLua::State) {
  x = LibLua.tonumberx(state, 1, nil)
  y = LibLua.tonumberx(state, 2, nil)

  # push result to stack
  LibLua.pushnumber(state, x + y)

  1 # number of results
}

# push crystal proc onto the stack
LibLua.pushcclosure(lua.state, proc, 0)

# give it a name
LibLua.setglobal(lua.state, "crystal_add")

# call crystal function with arguments.
pp lua.run %q{
  return 100 * crystal_add(3.0, 4.0)
} #=> 700.0

lua.close

So, basically, to achieve this, you need to create new method function on Stack (via new mixin) that will accept the function name and a block and do the work from the low-level example:

Having the number of block arguments, fetch them from the stack.
Call the block with those arguments and save the result. Note that Crystal can return only one argument as a function/proc result.
Push result back onto the stack

Crystal callback #15

Description

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions