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199 lines
6.6 KiB
Plaintext
199 lines
6.6 KiB
Plaintext
(doc Introspect
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"Dynamic functions that return information about the s-expressions associated
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to a binding.")
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(defmodule Introspect
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(doc module?
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"Is this binding a module?")
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(defndynamic module? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(Dynamic.= (Symbol.from "defmodule") (car s)))))
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(doc function?
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"Is this binding a function?")
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(defndynamic function? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(Dynamic.= (Symbol.from "defn") (car s)))))
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(doc command?
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"Is this binding a command?")
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(defndynamic command? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(Dynamic.= (Symbol.from "command") (car s)))))
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(doc primitive?
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"Is this binding a primitive?")
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(defndynamic primitive? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(Dynamic.= (Symbol.from "primitive") (car s)))))
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(doc external?
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"Is this binding external?")
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(defndynamic external? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(Dynamic.= (Symbol.from "external") (car s)))))
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(doc variable?
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"Is this binding a variable?")
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(defndynamic variable? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(Dynamic.= (Symbol.from "def") (car s)))))
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(doc type?
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"Is this binding a type?")
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(defndynamic type? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(Dynamic.= (Symbol.from "deftype") (car s)))))
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(doc struct?
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"Is this binding a struct?")
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(defndynamic struct? [binding]
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(let [s (s-expr binding)]
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(if (or (empty? s) (< (length s) 3))
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false
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(array? (caddr s)))))
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(doc sumtype?
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"Is this binding a sumtype?")
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(defndynamic sumtype? [binding]
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(let [s (s-expr binding)]
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(if (or (empty? s) (< (length s) 3))
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false
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(list? (caddr s)))))
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(doc implements? "Does `function` implement `interface`?")
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(defmacro implements? [interface function]
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(eval (list 'any?
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(list 'fn (array 'x) (list '= 'x interface))
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(list 'meta function "implements"))))
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(doc arity
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"What's the arity of this binding?
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- When `binding` is a function, returns the number of arguments.
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- When `binding` is a command, returns the number of arguments.
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- When `binding` is a primitive, returns the number of arguments.
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- When `binding` is an interface, returns the number of arguments.
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- When `binding` is a struct, returns the number of fields.
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- When `binding` is a sumtype, returns a list of the number of type
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arguments of each constructor.
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- Otherwise it returns 0.")
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(defndynamic arity [binding]
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(let [args (arguments binding)]
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(if (Introspect.sumtype? binding)
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(map length args)
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(length args))))
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(doc arguments
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"What are the arguments to this binding?
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- When `binding` is a function, returns the argument array.
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- When `binding` is a command, returns the argument array.
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- When `binding` is a primitive, returns the argument array.
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- When `binding` is an interface, returns the argument array.
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- When `binding` is a struct, returns the fields.
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- When `binding` is a sumtype, returns a list of the type arguments of each
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constructor.
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- Otherwise it returns an empty list.")
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(defndynamic arguments [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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0
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(cond
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(Introspect.external? binding)
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(if (list? (caddr s))
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(car (cdaddr s))
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'())
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(Introspect.command? binding) (caddr s)
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(Introspect.primitive? binding) (caddr s)
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(Introspect.interface? binding) (car (cdaddr s))
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(Introspect.function? binding) (caddr s)
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(Introspect.struct? binding) (map car (List.pairs (caddr s)))
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(Introspect.sumtype? binding) (map (fn [arr]
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(cadr arr)) (cddr s))
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'()))))
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(doc macro?
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"Is this binding a macro?")
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(defndynamic macro? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(Dynamic.= (Symbol.from "defmacro") (car s)))))
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(doc dynamic?
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"Is this binding a dynamic binding?")
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(defndynamic dynamic? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(or (Dynamic.= (Symbol.from "defdynamic") (car s))
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(Dynamic.= (Symbol.from "dynamic") (car s))))))
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(doc interface?
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"Is this binding an interface?")
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(defndynamic interface? [binding]
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(let [s (s-expr binding)]
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(if (empty? s)
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false
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(Dynamic.= (Symbol.from "definterface") (car s)))))
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(doc with-copy
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"Returns a reference to an anonymous 'proxied' variant of `function` in
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which the argument in position `arg` (indexed from 0) is *copied* from a
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reference before being passed to `function`:
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```
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;; Array.reduce expects a function that takes a *ref* in its second argument:
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;; (Fn [a (Ref b c)] ...)
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;; so we can't use a function like `+` directly; enter proxy
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(reduce (with-copy + 2) 0 &[1 2 3])
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=> 6
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;; compare this with an inline anonymous function that achieves the same thing:
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(reduce &(fn [x y] (+ x @y)) 0 &[1 2 3]) === (reduce (with-copy + 2) 0 &[1 2 3])
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```
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This is useful when using higher-order functions that operate over structures that
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return *references* to their inhabitants, such as arrays or structs. It allows
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you to use a function over values without writing a custom anonymous function
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to handle copying.
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Furthermore, one can define bespoke variants for working with particular
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higher-order functions. For instace, `reduce` always expacts a reference in the
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second positon:
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```
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(defmacro reducer [function]
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(eval (list with-copy function 2)))
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(reduce (reducer +) 0 &[1 2 3])
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=> 6
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```
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")
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(defmacro with-copy [function arg]
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;; The calls to `eval` around `function` are necessary to ensure we can execute arity.
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(let [arg-arr (Dynamic.unreduce inc 0 (Introspect.arity (eval function)) (array))
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;; increment arg by 1 to simulate indexing from 0--since the
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;; functions we rely on here return counts
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pos (+ arg 1)
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local-names (list-to-array-internal (map gensym-local (map Symbol.from arg-arr)) [])
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target (gensym-local (Symbol.from pos))
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prox (list 'copy target)
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call (cons function (map (fn [x] (if (= target x) prox x)) local-names))]
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(if (> pos (Introspect.arity (eval function)))
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(macro-error "with-copy error: the specified argument position is greater than the given function's arity.")
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(list 'ref (list 'fn local-names call)))))
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)
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