From 8a136eaa444f4569fced95fb175ca41b1e8e9b94 Mon Sep 17 00:00:00 2001 From: Andrey Orst Date: Tue, 17 Nov 2020 20:43:37 +0300 Subject: feature: major overhaul of documentation, and some housekeeping - remove(macros): `fn+` as it seem impractical, and `fn*` can be used instead - rename(def, defonce): `:dynamic` to `:mutable` as dynamic implies dynamic scoping which is not feature of Lua. - doc: generated documentation for macro module. --- doc/cljlib-macros.md | 631 ++++++++++++++++++++++++++++++++++----------------- 1 file changed, 426 insertions(+), 205 deletions(-) (limited to 'doc/cljlib-macros.md') diff --git a/doc/cljlib-macros.md b/doc/cljlib-macros.md index d99dad6..5916521 100644 --- a/doc/cljlib-macros.md +++ b/doc/cljlib-macros.md @@ -1,288 +1,509 @@ -# Cljlib-macros.fnl -Macro module for Fennel Cljlib. +# Cljlib-macros.fnl (0.1.0) +Macros for Cljlib that implement various facilities from Clojure. + +**Table of contents** + +- [`def`](#def) +- [`defmethod`](#defmethod) +- [`defmulti`](#defmulti) +- [`defonce`](#defonce) +- [`empty`](#empty) +- [`fn*`](#fn*) +- [`if-let`](#if-let) +- [`if-some`](#if-some) +- [`into`](#into) +- [`meta`](#meta) +- [`when-let`](#when-let) +- [`when-meta`](#when-meta) +- [`when-some`](#when-some) +- [`with-meta`](#with-meta) + +## `def` +Function signature: + +``` +(def attr-map? name expr) +``` + +Wrapper around `local` which can +declare variables inside namespace, and as local at the same time +similarly to [`fn*`](#fn*): + +``` fennel +(def ns {}) +(def a 10) ;; binds `a` to `10` + +(def ns.b 20) ;; binds `ns.b` and `b` to `20` +``` + +`a` is a `local`, and both `ns.b` and `b` refer to the same value. + +Additionally metadata can be attached to values, by providing +attribute map or keyword as first parameter. Only one keyword is +supported, which is `:mutable`, which allows mutating variable with +`set` later on: + +``` fennel +;; Bad, will override existing documentation for 299792458 (if any) +(def {:doc "speed of light in m/s"} c 299792458) +(set c 0) ;; => error, can't mutate `c` + +(def :mutable address "Lua St.") ;; same as (def {:mutable true} address "Lua St.") +(set address "Lisp St.") ;; can mutate `address` +``` + +However, attaching documentation metadata to anything other than +tables and functions considered bad practice, due to how Lua +works. More info can be found in [`with-meta`](#with-meta) +description. + +## `defmethod` +Function signature: + +``` +(defmethod multifn dispatch-val fnspec) +``` + +Attach new method to multi-function dispatch value. accepts the `multi-fn` +as its first argument, the dispatch value as second, and function tail +starting from argument list, followed by function body as in +[`fn*`](#fn). + +### Examples +Here are some examples how multimethods can be used. + +#### Factorial example +Key idea here is that multimethods can call itself with different +values, and will dispatch correctly. Here, `fac` recursively calls +itself with less and less number until it reaches `0` and dispatches +to another multimethod: + +``` fennel +(defmulti fac (fn [x] x)) + +(defmethod fac 0 [_] 1) +(defmethod fac :default [x] (* x (fac (- x 1)))) + +(fac 4) ;; => 24 +``` + +`:default` is a special method which gets called when no other methods +were found for given dispatch value. + +#### Multi-arity dispatching +Multi-arity function tails are also supported: + +``` fennel +(defmulti foo (fn* ([x] [x]) ([x y] [x y]))) + +(defmethod foo [10] [_] (print "I've knew I'll get 10")) +(defmethod foo [10 20] [_ _] (print "I've knew I'll get both 10 and 20")) +(defmethod foo :default ([x] (print (.. "Umm, got" x))) + ([x y] (print (.. "Umm, got both " x " and " y)))) +``` + +Calling `(foo 10)` will print `"I've knew I'll get 10"`, and calling +`(foo 10 20)` will print `"I've knew I'll get both 10 and 20"`. +However, calling `foo` with any other numbers will default either to +`"Umm, got x"` message, when called with single value, and `"Umm, got +both x and y"` when calling with two values. + +#### Dispatching on object's type +We can dispatch based on types the same way we dispatch on values. +For example, here's a naive conversion from Fennel's notation for +tables to Lua's one: + +``` fennel +(defmulti to-lua-str (fn [x] (type x))) -## Metadata macros -Metadata in Fennel is a pretty tough subject, as there's no such thing as metadata in Lua. -Therefore, the metadata usage in Fennel is more limited compared to Clojure. -This library provides some facilities for metadata management, which are experimental and should be used with care. +(defmethod to-lua-str :number [x] (tostring x)) +(defmethod to-lua-str :table [x] (let [res []] + (each [k v (pairs x)] + (table.insert res (.. "[" (to-lua-str k) "] = " (to-lua-str v)))) + (.. "{" (table.concat res ", ") "}"))) +(defmethod to-lua-str :string [x] (.. "\"" x "\"")) +(defmethod to-lua-str :default [x] (tostring x)) +``` -There are several important gotchas about using metadata. +And if we call it on some table, we'll get a valid Lua table: + +``` fennel +(print (to-lua-str {:a {:b 10}})) +;; prints {["a"] = {["b"] = 10}} + +(print (to-lua-str [:a :b :c [:d {:e :f}]])) +;; prints {[1] = "a", [2] = "b", [3] = "c", [4] = {[1] = "d", [2] = {["e"] = "f"}}} +``` + +Which we can then reformat as we want and use in Lua if we want. + +## `defmulti` +Function signature: + +``` +(defmulti name docstring? dispatch-fn attr-map?) +``` + +Create multifunction with +runtime dispatching based on results from `dispatch-fn`. Returns an +empty table with `__call` metamethod, that calls `dispatch-fn` on its +arguments. Amount of arguments passed, should be the same as accepted +by `dispatch-fn`. Looks for multimethod based on result from +`dispatch-fn`. + +By default, multifunction has no multimethods, see +[`multimethod`](#multimethod) on how to add one. + +## `defonce` +Function signature: -First, note that this works only when used with Fennel, and only when `(require fennel)` works. -For compiled Lua library this feature is turned off. +``` +(defonce attr-map? name expr) +``` + +Works the same as [`def`](#def), but ensures that later `defonce` +calls will not override existing bindings: -Second, try to avoid using metadata with anything else than tables and functions. -When storing function or table as a key into metatable, its address is used, while when storing string of number, the value is used. -This, for example, may cause documentation collision, when you've set some variable holding a number value to have certain docstring, and later you've defined another variable with the same value, but different docstring. -While this isn't a major breakage, it may confuse if someone will explore your code in the REPL with `doc`. +``` fennel +(defonce a 10) +(defonce a 20) +(print a) ;; => prints 10 +``` + +## `empty` +Function signature: + +``` +(empty x) +``` -Lastly, note that prior to Fennel 0.7.1 `import-macros` wasn't respecting `--metadata` switch. -So if you're using Fennel < 0.7.1 this stuff will only work if you use `require-macros` instead of `import-macros`. +Return empty table of the same kind as input table `x`, with +additional metadata indicating its type. +### Example +Creating a generic `map` function, that will work on any table type, +and return result of the same type: -### `when-meta` -This macros is a wrapper that compiles away if metadata support was not enabled. -What this effectively means, is that everything that is wrapped with this macro will disappear from the resulting Lua code if metadata is not enabled when compiling with `fennel --compile`. +``` fennel +(fn map [f tbl] + (let [res []] + (each [_ v (ipairs (into [] tbl))] + (table.insert res (f v))) + (into (empty tbl) res))) + +(map (fn [[k v]] [(string.upper k) v]) {:a 1 :b 2 :c 3}) +;; => {:A 1 :B 2 :C 3} +(map #(* $ $) [1 2 3 4]) +;; [1 4 9 16] +``` +See [`into`](#into) for more info on how conversion is done. +## `fn*` +Function signature: -### `with-meta` -Attach metadata to a value. +``` +(fn* name docstring? [arglist*] body* name docstring ([arglist*] body)*) +``` - >> (local foo (with-meta (fn [...] (let [[x y z] [...]] (+ x y z))) - {:fnl/arglist [:x :y :z :...] - :fnl/docstring "sum first three values"})) - >> (doc foo) - (foo x y z ...) - sum first three values +Create (anonymous) function of fixed arity. +Supports multiple arities by defining bodies as lists: -When metadata feature is not enabled, returns the value without additional metadata. +### Examples +Named function of fixed arity 2: +``` fennel +(fn* f [a b] (+ a b)) +``` -### `meta` -Get metadata table from object: +Function of fixed arities 1 and 2: - >> (meta (with-meta {} {:meta "data"})) - { - :meta "data" - } +``` fennel +(fn* ([x] x) + ([x y] (+ x y))) +``` +Named function of 2 arities, one of which accepts 0 arguments, and the +other one or more arguments: -## `def` and `defonce` -`def` is wrappers around `local` which can declare variables inside namespace, and as local at the same time: +``` fennel +(fn* f + ([] nil) + ([x & xs] + (print x) + (f (unpack xs)))) +``` - >> (def ns {}) - >> (def a 10) - >> a - 10 - >> (def ns.a 20) - >> a - 20 - >> ns.a - 20 +Note, that this function is recursive, and calls itself with less and +less amount of arguments until there's no arguments, and terminates +when the zero-arity body is called. -Both `ns.a` and `a` refer to the same value. +Named functions accept additional documentation string before the +argument list: -`defonce` ensures that the binding isn't overridden by another `defonce`: +``` fennel +(fn* cube + "raise `x` to power of 3" + [x] + (^ x 3)) - >> (defonce ns {}) - >> (defonce ns.a 42) - >> (defonce ns 10) - >> ns - {:a 42} - >> a - 42 +(fn* greet + "greet a `person`, optionally specifying default `greeting`." + ([person] (print (.. "Hello, " person "!"))) + ([greeting person] (print (.. greeting ", " person "!")))) +``` -Both `def` and `defonce` support literal metadata table as first argument, or a :dynamic keyword, that uses Fennel `var` instead of `local`: +Argument lists follow the same destruction rules as per `let`. +Variadic arguments with `...` are not supported use `& rest` instead. +Note that only one arity with `&` is supported. - >> (def {:dynamic true} a 10) - >> (set a 20) - >> a - 20 - >> (defonce :dynamic b 40) - >> (set b 42) - >> b - 42 +##### Namespaces +If function name contains namespace part, defines local variable +without namespace part, then creates function with this name, sets +this function to the namespace, and returns it. -Documentation string can be attached to value via `:doc` keyword. -However it is not recommended to attach metadata to everything except tables and functions: +This roughly means, that instead of writing this: - ;; Bad, may overlap with existing documentation for 299792458, if any - >> (def {:doc "The speed of light in m/s"} c 299792458) - >> (doc c) - c - The speed of light in m/s +``` fennel +(local ns {}) - ;; OK - >> (def {:doc "default connection options"} - defaults {:port 1234 - :host localhost}) +(fn f [x] ;; we have to define `f` without `ns` + (if (> x 0) (f (- x 1)))) ;; because we're going to use it in `g` +(set ns.f f) -## `fn*` -Clojure's `fn` equivalent. -Returns a function of fixed amount of arguments by doing runtime dispatch based on argument count. -Capable of producing multi-arity functions: +(fn ns.g [x] (f (* x 100))) ;; `g` can be defined as `ns.g` as it is only exported - (fn* square "square number" [x] (^ x 2)) +ns +``` - (square 9) ;; => 81.0 - (square 1 2) ;; => error +It is possible to write: - (fn* range - "Returns increasing sequence of numbers from `lower' to `upper'. - If `lower' is not provided, sequence starts from zero. - Accepts optional `step'" - ([upper] (range 0 upper 1)) - ([lower upper] (range lower upper 1)) - ([lower upper step] - (let [res []] - (for [i lower (- upper step) step] - (table.insert res i)) - res))) +``` fennel +(local ns {}) - (range 10) ;; => [0 1 2 3 4 5 6 7 8 9] - (range -10 0) ;; => [-10 -9 -8 -7 -6 -5 -4 -3 -2 -1] - (range 0 1 0.2) ;; => [0.0 0.2 0.4 0.6 0.8] +(fn* ns.f [x] + (if (> x 0) (f (- x 1)))) -Both variants support up to one arity with `& more`: +(fn* ns.g [x] (f (* x 100))) ;; we can use `f` here no problem - (fn* vec [& xs] xs) +ns +``` - (vec 1 2 3) ;; => [1 2 3] +It is still possible to call `f` and `g` in current scope without `ns` +part, so functions can be reused inside the module, and `ns` will hold +both functions, so it can be exported from the module. - (fn* add - "sum two or more values" - ([] 0) - ([a] a) - ([a b] (+ a b)) - ([a b & more] (add (+ a b) (unpack more)))) +Note that `fn` will not create the `ns` for you, hence this is just a +syntax sugar. Functions deeply nested in namespaces require exising +namespace tables: - (add) ;; => 0 - (add 1) ;; => 1 - (add 1 2) ;; => 3 - (add 1 2 3 4) ;; => 10 +``` fennel +(local ns {:strings {} + :tables {}}) -One extra capability of `fn*` supports the same semantic as `def` regarding namespaces: +(fn* ns.strings.join + ([s1 s2] (.. s1 s2)) + ([s1 s2 & strings] + (join (join s1 s2) (unpack strings)))) ;; call `join` resolves to ns.strings.join - (local ns {}) +(fn* ns.tables.join + ([t1 t2] + (let [res []] + (each [_ v (ipairs t1)] (table.insert res v)) + (each [_ v (ipairs t2)] (table.insert res v)) + res)) + ([t1 t2 & tables] + (join (join t1 t2) (unpack tables)))) ;; call to `join` resolves to ns.tables.join +``` - (fn* ns.plus - ([] 0) - ([x] x) - ([x y] (+ x y)) - ([x y & zs] (apply plus (+ x y) zs))) +Note that this creates a collision and local `join` overrides `join` +from `ns.strings`, so the latter must be fully qualified +`ns.strings.join` when called outside of the function: - ns +``` fennel +(ns.strings.join "a" "b" "c") +;; => abc +(join ["a"] ["b"] ["c"] ["d" "e"]) +;; => ["a" "b" "c" "d" "e"] +(join "a" "b" "c") +;; {} +``` -Note, that `plus` is used without `ns` part, e.g. not `ns.plus`. -If we `require` this code from file in the REPL, we will see that our `ns` has single function `plus`: +## `if-let` +Function signature: - >> (local ns (require :module)) - >> ns - {add #} +``` +(if-let [binding test] then-branch else-branch) +``` -This is possible because `fn*` separates the namespace part from the function name, and creates a `local` variable with the same name as function, then defines the function within lexical scope of `do`, sets `namespace.foo` to it and returns the function object to the outer scope. +If test is logical true, +evaluates `then-branch` with binding-form bound to the value of test, +if not, yields `else-branch`. - (local plus - (do (fn plus [...] - ;; plus body - ) - (set ns.plus plus) - plus)) +## `if-some` +Function signature: -See `core.fnl` for more examples. +``` +(if-some [binding test] then-branch else-branch) +``` +If test is non-`nil`, evaluates +`then-branch` with binding-form bound to the value of test, if not, +yields `else-branch`. -## `fn+` -Works similarly to Fennel's `fn`, by creating ordinary function without arity semantics, except does the namespace automation like `fn*`, and has the same order of arguments as the latter: +## `into` +Function signature: - (local ns {}) +``` +(into to from) +``` - ;; module & file-local functions - (fn+ ns.double - "double the number" - [x] - (* x 2)) +Transform one table into another. Mutates first table. - (fn+ ns.triple - [x] - (* x 3)) +Transformation happens in runtime, but type deduction happens in +compile time if possible. This means, that if literal values passed +to `into` this will have different effects for associative tables and +vectors: - ;; no namespace, file-local function - (fn+ quadruple - [x] - (* x 4)) +``` fennel +(into [1 2 3] [4 5 6]) ;; => [1 2 3 4 5 6] +(into {:a 1 :c 2} {:a 0 :b 1}) ;; => {:a 0 :b 1 :c 2} +``` - ;; anonymous file-local function - (fn+ [x] (* x 5)) +Conversion between different table types is also supported: - ns +``` fennel +(into [] {:a 1 :b 2 :c 3}) ;; => [[:a 1] [:b 2] [:c 3]] +(into {} [[:a 1] [:b 2]]) ;; => {:a 1 :b 2} +``` -See `core.fnl` for more examples. +Same rules apply to runtime detection of table type, except that this +will not work for empty tables: +``` fennel +(local empty-table {}) +(into empty-table {:a 1 :b 2}) ;; => [[:a 1] [:b 2]] +``` fennel -## `if-let` and `when-let` -When test expression is not `nil` or `false`, evaluates the first body form with the `name` bound to the result of the expressions. +If table is empty, `into` defaults to sequential table, because it +allows safe conversion from both sequential and associative tables. - (if-let [val (test)] - (print val) - :fail) +Type for non empty tables hidden in variables can be deduced at +runtime, and this works as expected: -Expanded form: +``` fennel +(local t1 [1 2 3]) +(local t2 {:a 10 :c 3}) +(into t1 {:a 1 :b 2}) ;; => [1 2 3 [:a 1] [:b 2]] +(into t2 {:a 1 :b 2}) ;; => {:a 1 :b 2 :c 3} +``` - (let [tmp (test)] - (if tmp - (let [val tmp] - (print val)) - :fail)) +`cljlib.fnl` module provides two additional functions `vector` and +`hash-map`, that can create empty tables, which can be distinguished +at runtime: -`when-let` is mostly the same, except doesn't have false branch and accepts any amount of forms: +``` fennel +(into (vector) {:a 1 :b 2}) ;; => [[:a 1] [:b 2]] +(into (hash-map) [[:a 1 :b 2]]) ;; => {:a 1 :b 2} +``` - (when-let [val (test)] - (print val) - val) +## `meta` +Function signature: -Expanded form: +``` +(meta value) +``` - (let [tmp (test)] - (if tmp - (let [val tmp] - (print val) - val))) +Get `value` metadata. If value has no metadata, or metadata +feature is not enabled returns `nil`. +### Example -## `if-some` and `when-some` -Much like `if-let` and `when-let`, except tests expression for not being `nil`. +``` fennel +>> (meta (with-meta {} {:meta "data"})) +;; => {:meta "data"} +``` - (when-some [val (foo)] - (print (.. "val is not nil: " val)) - val) +### Note +There are several important gotchas about using metadata. +First, note that this works only when used with Fennel, and only when +`(require fennel)` works. For compiled Lua library this feature is +turned off. -## `into` -Clojure's `into` function is implemented as macro, because Fennel has no runtime distinction between `[]` and `{}` tables, since Lua also doesn't feature this feature. -However we can do this at compile time. +Second, try to avoid using metadata with anything else than tables and +functions. When storing function or table as a key into metatable, +its address is used, while when storing string of number, the value is +used. This, for example, may cause documentation collision, when +you've set some variable holding a number value to have certain +docstring, and later you've defined another variable with the same +value, but different docstring. While this isn't a major breakage, it +may confuse if someone will explore your code in the REPL with `doc`. + +Lastly, note that prior to Fennel 0.7.1 `import-macros` wasn't +respecting `--metadata` switch. So if you're using Fennel < 0.7.1 +this stuff will only work if you use `require-macros` instead of +`import-macros`. + +## `when-let` +Function signature: + +``` +(when-let [binding test] & body) +``` + +If test is logical true, +evaluates `body` in implicit `do`. + +## `when-meta` +Function signature: - (into [1 2 3] [4 5 6]) ;; => [1 2 3 4 5 6] - (into [] {:a 1 :b 2 :c 3 :d 4}) ;; => [["d" 4] ["a" 1] ["b" 2] ["c" 3]] - (into {} [[:d 4] [:a 1] [:b 2] [:c 3]]) ;; => {:a 1 :b 2 :c 3 :d 4} - (into {:a 0 :e 5} {:a 1 :b 2 :c 3 :d 4}) ;; => {:a 1 :b 2 :c 3 :d 4 :e 5} +``` +(when-meta [& body]) +``` -Because the type check at compile time it will only respect the type when literal representation is used. -If a variable holding the table, its type is checked at runtime. -Empty tables default to sequential ones: +Wrapper that compiles away if metadata support was not enabled. What +this effectively means, is that everything that is wrapped with this +macro will disappear from the resulting Lua code if metadata is not +enabled when compiling with `fennel --compile` without `--metadata` +switch. - (local a []) - (into a {:a 1 :b 2}) ;; => [["b" 2] ["a" 1]] +## `when-some` +Function signature: - (local b {}) - (into b {:a 1 :b 2}) ;; => [["b" 2] ["a" 1]] +``` +(when-some [binding test] & body) +``` -However, if target table is not empty, its type can be deduced: +If test is non-`nil`, +evaluates `body` in implicit `do`. - (local a {:c 3}) - (into a {:a 1 :b 2}) ;; => {:a 1 :b 2 :c 3} +## `with-meta` +Function signature: - (local b [1]) - (into b {:a 1 :b 2}) ;; => [1 ["b" 2] ["a" 1]] +``` +(with-meta value meta) +``` -Note that when converting associative table into sequential table order is determined by the `pairs` function. -Also note that if variable stores the table has both integer key 1, and other associative keys, the type will be the same as of sequential table. +Attach metadata to a value. When metadata feature is not enabled, +returns the value without additional metadata. +``` fennel +>> (local foo (with-meta (fn [...] (let [[x y z] [...]] (+ x y z))) + {:fnl/arglist ["x" "y" "z" "..."] + :fnl/docstring "sum first three values"})) +>> (doc foo) +(foo x y z ...) + sum first three values +``` -## `defmulti` and `defmethod` -A bit more simple implementations of Clojure's `defmulti` and `defmethod`. -`defmulti` macros returns an empty table with `__call` metamethod, that calls dispatching function on its arguments. -Methods are defined inside `multimethods` table, which is also stored in the metatable. -`defmethod` adds a new method to the metatable of given `multifn`. -It accepts the multi-fn table as its first argument, the dispatch value as second, and Fennel's arglist followed by the body: +--- - (defmulti fac (fn [x] x)) +Copyright (C) 2020 Andrey Orst - (defmethod fac 0 [_] 1) - (defmethod fac :default [x] (* x (fac (- x 1)))) +License: [MIT](https://gitlab.com/andreyorst/fennel-cljlib/-/raw/master/LICENSE) - (fac 4) ;; => 24 -`:default` is a special method which gets called when no other methods were found for given dispatch value. + -- cgit v1.2.3