Try to figure it out on your own, then come back with the code if you can't do it. I'm not lazy the code is shorter than this comment.
An assert macro with informative failure reports, as a syntax-rule or a defmacro. A concise definition form with optional arguments and default values MetaScheme, or untyped MetaOCaml and the underlying alpha-conversion macro Applicative syntax-rules: It is very difficult to write macros that compose, to assemble complex macros from already written and tested components.
The previous approaches to composable syntax-rules are heavy, notationally and computationally. This article presents an alternative, lightweight style of writing composable syntax-rules, based on the CK abstract machine. We demonstrate recursive, higher-order applicative macros defined in the style that looks like that of ML or strict Haskell.
We write composable, call-by-value--like macros without resorting to the continuation-passing-style and thus requiring no macro-level lambda. The syntax remains direct-style, with nested applications.
Syntax-rules are difficult to compose because of their evaluation order: That per se does not preclude functional composition since the normal-order lambda-calculus or non-strict languages like Haskell do not evaluate arguments of a function application either.
However, lambda-calculus has first-class anonymous abstractions; Haskell also has the case form that forces evaluation of an expression, to the extent needed to choose among the pattern-match clauses.
Syntax-rules have none of these compensating features. Generally, a syntax-rule cannot obtain the result of the expansion of its argument expression.
The article on Systematic Macro Programming on this page explains the composability problem in detail.
So far, the only way out has been to effectively change the evaluation order by writing macros in the continuation-passing style CPS. However, CPS code is hard to read. Furthermore, building continuations requires the notation for first-class, preferably anonymous syntax-rule abstractions.
Although the latter are possible to emulate, the result is stylistically ugly and computationally expensive. Some macro expanders take the shocking amount of time and memory to expand CPS macros with anonymous abstractions. This project was inspired by the question posed by Dan Friedman in March Write the macro permute that takes any number of arguments and returns the list of their permutations: One should write permute without resorting to CPS.
Our answer is the transliteration of the standard Haskell code implementing the straightforward algorithm for all permutations: Our macros are written in a CK style. We distinguish values, which are always quoted like ' 1 2 3from general applicative expressions such as c-append ' 1 c-cons '2 ' 3 4which may contain nested applications.
Values are regarded as results of the CK evaluation. Here is the first example, of the CK-style macro cons: The macro should never look at s, passing it to the macro ck described below.
All arguments of a CK-macro except for s are always values; the macro is free to pattern-match on them. A CK-macro always expands into the call to the macro ck, passing it the s argument followed by the produced value or by the expression that will produce the resulting value.Recursion in computer science is a method of solving a problem where the solution depends on solutions to smaller instances of the same problem (as opposed to iteration).
The approach can be applied to many types of problems, and recursion is one of the central ideas of computer science.. The power of recursion evidently lies in the possibility of defining an infinite set of objects by a.
Functions . A function, which can also be referred to as subroutine, procedure, subprogram or even method, carries out tasks defined by a sequence of statements called a statement block that need only be written once and called by a program as many times as needed to carry out the same task..
Functions may depend on variables passed to them, called arguments, and may pass results of a task. Catalan numbers You are encouraged to solve this task according to the task description, using any language you may know.
Code for Prolog program to find factorial of given number in Artificial Intelligence predicates start find_factorial(real,real) goal clearwindow, start. 8 PL/SQL Subprograms. Civilization advances by extending the number of important operations that we can perform without thinking about them.
--Alfred North WhiteheadThis chapter shows you how to use subprograms, which let you name and encapsulate a sequence of statements. Cabal is the build system for Haskell.. For example, to install the parsec package to your system from Hackage, the upstream source of Haskell packages, invoke the install command: $ cabal install parsec # latest version $ cabal install parsec== # exact version.