Subj : Re: OO compilers and efficiency
To   : comp.programming
From : Chris Dollin
Date : Wed Jul 27 2005 10:38 am

Chris Dollin wrote:

> Functional programs have if-then-else. What they don't have is
> updatable locations.

Probably I should say that *pure* functional *languages* don't have
update. Impure FLs - eg ML, Scheme - have limited update and lots
of idioms that don't use it.

[My excuse is that I spent too much time in an environment when
 "functional" implied "pure", and it hasn't worn off yet.]

So, to be positive, what do functional programs - better, languages - 
have (or tend to have)? A non-exhaustive list includes:

* functions as first-class objects, so any function can be passed
  as an argument or returned as a result, capturing any bound
  non-local variables [ie thay are "closures"]

* notation for function-expressions, so you can write anonymous
  functions, eg   (x => x + 1) to denote "the [a] function that 
  adds one to things". Sometimes this includes operator abbreviation
  such as (1.0 /), "reciprocal". 

* [Sometimes] strong static inferred typing, which gives a lot
  of the benefits of compile-time type-checking without the
  syntactic litter

* [Sometimes] compact definitions of data-types like tuples,
  records, and tagged unions, often with syntactic sugar for
  decomposing them ...

* ... using pattern-matching in function definitions. 

EG, and with no particular syntax,

    type List T = nil | cons of (hd: T x tl: List T)

    def length nil = 0
    |   length cons of (h, t) = 1 + length t


-- 
Chris "electric hedgehog" Dollin
predicting self-predictors' predictions is predictably unpredictable.

.