Idea
In functional languages, a function is a value. So, passing or returning a function is merely passing / returning a value. The principle is simple.
But, applying this simple principle might troublesome when we introduce higher-order-functional feature to an existing language.
There is a modest solution; we will introduce one additional type Thunk to the JSON-base type system.
Definitions
- a thunk is an opaque value that represents a function. a thunk is not a function itself, but a value. You may think of a thunk as a frozen function.
- the asterisk symbol '*' defrosts a thunk. A thunk is activated by prefixed '*', and it can work as a function
- the ampersand symbol '&' freezes (i.e. creates thunk from) an actual function.
&foois a value that you can freely pass / return.
Dynamically created thunk
Specification of the function dyn_def :
dyn_def(params: string, body: string) : IGNORE -> Thunk- params : a string that is, when parsed, syntactically valid function parameter declaration.
- body : a string that is, when parsed, syntactically valid function body.
dyn_defignores her input.dyn_defreturns a thunk -- the value which represents a defined function.
10 | dyn_def("(a, b)", "a * . + b") as $linear_function | *$linear_function(2, 5) # => 2 * 10 + 5 = 25
