From 823441e43dd007d4e8931fb236ffbeada12eabd2 Mon Sep 17 00:00:00 2001 From: bnewbold Date: Wed, 14 Jan 2009 16:24:34 -0500 Subject: bunch of new --- software/functional programming | 52 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) create mode 100644 software/functional programming (limited to 'software/functional programming') diff --git a/software/functional programming b/software/functional programming new file mode 100644 index 0000000..4720280 --- /dev/null +++ b/software/functional programming @@ -0,0 +1,52 @@ +=================================== +Functional Programming +=================================== + +Recursion +-------------- +**Partial** functions can recurse endlessly over a finite input. **Total** +functions will terminate/halt over a finite input. (TODO: check this +definition) + +Collectors +-------------- +The collector concept/pattern/paradigm is the one I am least familiar with +in functional programming. + +My current understanding is that they essentially allow allow recursive +functions to maintain something like state by wrapping immutable functions +or variables in layer after layer of functions and just holding on to +the outermost layer. For instance, the typical way to write a ``length`` +function in python would be:: + +>>> def how-long(x): +>>> l = 0 +>>> while x.has_next() +>>> l = l+1; +>>> x.pop() +>>> return l + +Using recursion, we could do:: + +>>> def how-long-recurse(x): +>>> if x.has_next() +>>> x.pop() +>>> return how-long-recurse(x) + 1 +>>> else +>>> return 0 + +Using the collector paradigm, we could do:: + +>>> def add1(x): return a+1; +>>> def how-long-col(x, col): +>>> if x.has_next() +>>> return col(0) +>>> else +>>> x.pop() +>>> return how-long-col(x, lambda a: col(add1(a))) + +The first two ways, the plus one operation is actually executed at any given +time, while with the collector implementation we're really creating a +function step by step which will give the answer at the end when it is all +executed. + -- cgit v1.2.3