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289 lines
6.6 KiB
D
289 lines
6.6 KiB
D
// Written in the D programming language.
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/**
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Functions that manipulate other functions.
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Macros:
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WIKI = Phobos/StdFunctional
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Author:
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$(WEB erdani.org, Andrei Alexandrescu)
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*/
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/*
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* Copyright (C) 2004-2006 by Digital Mars, www.digitalmars.com
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* Written by Andrei Alexandrescu, www.erdani.org
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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*
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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*
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* o The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* o Altered source versions must be plainly marked as such, and must not
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* be misrepresented as being the original software.
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* o This notice may not be removed or altered from any source
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* distribution.
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*/
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module std.functional;
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import std.string; // for making string functions visible in *naryFun
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import std.conv; // for making conversions visible in *naryFun
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import std.typetuple;
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import std.typecons;
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import std.stdio;
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import std.metastrings;
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/**
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Transforms a string representing an expression into a unary
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function. The string must use symbol name $(D a) as the parameter.
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Example:
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----
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alias unaryFun!("(a & 1) == 0") isEven;
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assert(isEven(2) && !isEven(1));
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----
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*/
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template unaryFun(string comp, bool byRef = false) {
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static if (byRef)
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{
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void unaryFun(ElementType)(ref ElementType a)
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{
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mixin(comp ~ ";");
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}
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}
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else
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{
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// @@@BUG1816@@@: typeof(mixin(comp)) should work
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typeof({ ElementType a; return mixin(comp);}())
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unaryFun(ElementType)(ElementType a)
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{
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return mixin(comp);
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}
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}
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}
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/**
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Transforms a string representing an expression into a Boolean binary
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predicate. The string must use symbol names $(D a) and $(D b) as the
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compared elements.
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Example:
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----
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alias binaryFun!("a < b") less;
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assert(less(1, 2) && !less(2, 1));
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alias binaryFun!("a > b") greater;
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assert(!greater("1", "2") && greater("2", "1"));
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----
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*/
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template binaryFun(string comp)
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{
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// @@@BUG1816@@@: typeof(mixin(comp)) should work
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typeof({
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static ElementType1 a;
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static ElementType2 b;
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return mixin(comp);
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}())
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binaryFun(ElementType1, ElementType2)(ElementType1 a, ElementType2 b)
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{
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return mixin(comp);
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}
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}
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unittest
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{
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alias binaryFun!(q{a < b}) less;
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assert(less(1, 2) && !less(2, 1));
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assert(less("1", "2") && !less("2", "1"));
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}
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/*
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Predicate that returns $(D_PARAM a < b).
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*/
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//bool less(T)(T a, T b) { return a < b; }
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//alias binaryFun!(q{a < b}) less;
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/*
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Predicate that returns $(D_PARAM a > b).
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*/
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//alias binaryFun!(q{a > b}) greater;
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/*
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Predicate that returns $(D_PARAM a == b).
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*/
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//alias binaryFun!(q{a == b}) equalTo;
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/*
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Binary predicate that reverses the order of arguments, e.g., given
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$(D pred(a, b)), returns $(D pred(b, a)).
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*/
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template binaryRevertArgs(alias pred)
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{
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typeof({ ElementType1 a; ElementType2 b; return pred(b, a);}())
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binaryRevertArgs(ElementType1, ElementType2)(ElementType1 a, ElementType2 b)
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{
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return pred(b, a);
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}
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}
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unittest
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{
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alias binaryRevertArgs!(binaryFun!("a < b")) gt;
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assert(gt(2, 1) && !gt(1, 1));
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int x = 42;
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bool xyz(int a, int b) { return a * x < b / x; }
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auto foo = &xyz;
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foo(4, 5);
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alias binaryRevertArgs!(foo) zyx;
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assert(zyx(5, 4) == foo(4, 5));
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}
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template not(alias pred)
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{
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bool not(T...)(T args) { return !pred(args); }
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}
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/*private*/ template Adjoin(F...)
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{
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template For(V...)
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{
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static if (F.length == 0)
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{
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alias TypeTuple!() Result;
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}
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else
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{
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alias F[0] headFun;
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alias typeof({ V values; return headFun(values); }()) Head;
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alias TypeTuple!(Head, Adjoin!(F[1 .. $]).For!(V).Result) Result;
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}
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}
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}
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/**
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Takes multiple functions and adjoins them together. The result is a
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$(XREF typecons, Tuple) with one element per passed-in function. Upon
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invocation, the returned tuple is the adjoined results of all
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functions.
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Example:
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----
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static bool f1(int a) { return a != 0; }
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static int f2(int a) { return a / 2; }
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auto x = adjoin!(f1, f2)(5);
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assert(is(typeof(x) == Tuple!(bool, int)));
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assert(x._0 == true && x._1 == 2);
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----
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*/
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template adjoin(F...)
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{
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Tuple!(Adjoin!(F).For!(V).Result) adjoin(V...)(V a)
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{
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typeof(return) result;
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foreach (i, r; F)
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{
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// @@@BUG@@@
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mixin("result.field!("~ToString!(i)~") = F[i](a);");
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}
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return result;
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}
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}
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unittest
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{
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static bool F1(int a) { return a != 0; }
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static int F2(int a) { return a / 2; }
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auto x = adjoin!(F1, F2)(5);
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alias Adjoin!(F1, F2).For!(int).Result R;
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assert(is(typeof(x) == Tuple!(bool, int)));
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assert(x._0 == true && x._1 == 2);
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}
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// /*private*/ template NaryFun(string fun, string letter, V...)
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// {
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// static if (V.length == 0)
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// {
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// enum args = "";
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// }
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// else
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// {
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// enum args = V[0].stringof~" "~letter~"; "
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// ~NaryFun!(fun, [letter[0] + 1], V[1..$]).args;
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// enum code = args ~ "return "~fun~";";
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// }
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// alias void Result;
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// }
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// unittest
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// {
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// writeln(NaryFun!("a * b * 2", "a", int, double).code);
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// }
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// /**
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// naryFun
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// */
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// template naryFun(string fun)
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// {
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// //NaryFun!(fun, "a", V).Result
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// int naryFun(V...)(V values)
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// {
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// enum string code = NaryFun!(fun, "a", V).code;
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// mixin(code);
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// }
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// }
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// unittest
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// {
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// alias naryFun!("a + b") test;
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// test(1, 2);
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// }
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/**
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Composes two functions $(D F1) and $(D F2), returning a function $(D
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F(x)) that in turn returns $(D F1(F2(x))).
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Example:
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----
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auto x = 5;
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auto y = compose!("!a", "a > 0")(x);
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assert(!y);
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----
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*/
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template compose(alias F1, alias F2)
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{
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typeof({ E a; return F1(F2(a)); }()) compose(E)(E a)
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{
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return F1(F2(a));
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}
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}
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/// Ditto
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template compose(alias F1, string F2)
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{
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alias .compose!(F1, unaryFun!(F2)) compose;
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}
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/// Ditto
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template compose(string F1, alias F2)
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{
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alias .compose!(unaryFun!(F1), F2) compose;
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}
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/// Ditto
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template compose(string F1, string F2)
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{
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alias .compose!(unaryFun!(F1), unaryFun!(F2)) compose;
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}
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