alias-hacks

aliases for common clojure names to mal builtins

• let / when / def / fn / defn
• partial

benchmark

• benchmark
  An alternative approach, to complement perf

equality

This file checks whether the = function correctly implements equality of hash-maps and sequences (lists and vectors). If not, it redefines the = function with a pure mal (recursive) implementation that only relies on the native original = function for comparing scalars (integers, booleans, symbols, strings, keywords, atoms, nil).

• scalar-equal?
  Save the original (native) = as scalar-equal?
• mal-equal?
  This implements = in pure mal (using only scalar-equal? as native impl)

load-file-once

• load-file-once
  Like load-file, but will never load the same path twice.

memoize

Memoize any function.

• memoize
  Implement memoize using an atom (mem) which holds the memoized results (hash-map from the arguments to the result). When the function is called, the hash-map is checked to see if the result for the given argument was already calculated and stored. If this is the case, it is returned immediately; otherwise, it is calculated and stored in mem.
  For recursive functions, take care to store the wrapper under the same name than the original computation with an assignment like (def! f (memoize f)), so that intermediate results are memorized.

perf

Mesure performances.

• time
  Evaluate an expression, but report the time spent
• run-fn-for
  Count evaluations of a function during a given time frame.

    ;; fn       : function without parameters;; max-secs : number (seconds);; return   : number (iterations)
  

pprint

• pprint
  Pretty printer a MAL object.

protocols

A sketch of Clojure-like protocols, implemented in Mal.

• find-type
  This function maps a MAL value to a keyword representing its type.
  Most applications will override the default with an explicit value for the :type key in the metadata.
• defprotocol
  A protocol (abstract class, interface…) is represented by a symbol.
  It describes methods (abstract functions, contracts, signals…).
  Each method is described by a sequence of two elements.
  First, a symbol setting the name of the method.
  Second, a vector setting its formal parameters.
  The first parameter is required, plays a special role.
  It is usually named this (self…).
  For example,

     (defprotocol protocol(method1 [this])(method2 [this argument]))
  ;; can be thought as:(def! method1 (fn* [this]) ..)(def! method2 (fn* [this argument]) ..)(def! protocol ..)
  ;; The return value is the new protocol.
  

  A protocol is an atom mapping a type extending the protocol to another map from method names as keywords to implementations.
• extend
  A type (concrete class…) extends (is a subclass of, implements…) a protocol when it provides implementations for the required methods.

     (extend type protocol {:method1 (fn* [this] ..):method2 (fn* [this arg1 arg2])})
  

  Additional protocol/methods pairs are equivalent to successive calls with the same type.
  The return value is nil.
• satisfies?
  An object satisfies a protocol when its type extends the protocol, that is if the required methods can be applied to the object.
  If (satisfies protocol obj) with the protocol below then (method1 obj) and (method2 obj 1 2) dispatch to the concrete implementation provided by the exact type.
  Should the type evolve, the calling code needs not change.

reducers

Left and right folds.

• reduce
  Left fold (f (… (f (f init x1) x2) …) xn)
• foldr
  Right fold (f x1 (f x2 (… (f xn init)) …))
  The natural implementation for foldr is not tail-recursive, and the one based on reduce constructs many intermediate functions, so we rely on efficient nth and count.

test_cascade

Iteration on evaluations interpreted as boolean values.

• or
(or x1 x2 .. xn x) is almost rewritten as (if x1 x1 (if x2 x2 (.. (if xn xn x)))) except that each argument is evaluated at most once.
  Without arguments, returns nil.
• every?
  Conjonction of predicate values (pred x1) and … and (pred xn)
  Evaluate (pred x) for each x in turn. Return false if a result is nil or false, without evaluating the predicate for the remaining elements. If all test pass, return true.
• some
  Disjonction of predicate values (pred x1) or … (pred xn)
  Evaluate (pred x) for each x in turn. Return the first result that is neither nil nor false, without evaluating the predicate for the remaining elements. If all tests fail, return nil.
• and
  Search for first evaluation returning nil or false.
  Without arguments, returns true.

threading

Composition of partially applied functions.

• ->
  Rewrite x (a a1 a2) .. (b b1 b2) as (b (.. (a x a1 a2) ..) b1 b2)
  If anything else than a list is found where (a a1 a2) is expected, replace it with a list with one element, so that -> x a is equivalent to -> x (list a).
• ->>
  Like ->, but the arguments describe functions that are partially applied with left arguments. The previous result is inserted at the end of the new argument list.
  Rewrite x (a a1 a2) .. (b b1 b2) as (b b1 b2 (.. (a a1 a2 x) ..)).

trivial

Trivial but convenient functions.

• inc / dec / zero? / identity
• gensym
  Generate a hopefully unique symbol.