Pure (programming language)
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Developer Albert Gräf | | |
| First appeared | 2008 | |
|---|---|---|
| Stable release | 0.68
/ 11 April 2018 | |
Pure, successor to the equational language Q, is a dynamically typed,
Overview
Pure comes with an interpreter and debugger, provides automatic memory management, has powerful functional and symbolic programming abilities, and interfaces to
The Pure language is a successor of the equational programming language Q, previously created by the same author, Albert Gräf at the
Pure plug-ins are available for the Gnumeric spreadsheet and Miller Puckette's Pure Data graphical multimedia software, which make it possible to extend these programs with functions written in the Pure language. Interfaces are also provided as library modules to GNU Octave, OpenCV, OpenGL, the GNU Scientific Library, FAUST, SuperCollider, and liblo (for Open Sound Control (OSC)).
Examples
The
fib 0 = 0;
fib 1 = 1;
fib n = fib (n-2) + fib (n-1) if n>1;
Better (
fib n = fibs (0,1) n with
fibs (a,b) n = if n<=0 then a else fibs (b,a+b) (n-1);
end;
Compute the first 20 Fibonacci numbers:
map fib (1..20);
An algorithm for the n queens problem which employs a list comprehension to organize the backtracking search:
queens n = search n 1 [] with
search n i p = [reverse p] if i>n;
= cat [search n (i+1) ((i,j):p) | j = 1..n; safe (i,j) p];
safe (i,j) p = ~any (check (i,j)) p;
check (i1,j1) (i2,j2)
= i1==i2 || j1==j2 || i1+j1==i2+j2 || i1-j1==i2-j2;
end;
While Pure uses
primes = sieve (2..inf) with
sieve (p:qs) = p : sieve [q | q = qs; q mod p] &;
end;
Use of the & operator turns the tail of the sieve into a
primes!!(0..99); // yields the first 100 primes
Pure has efficient support for vectors and matrices (similar to that of
gauss_elimination x::matrix = p,x
when n,m = dim x; p,_,x = foldl step (0..n-1,0,x) (0..m-1) end;
step (p,i,x) j
= if max_x==0 then p,i,x else
// updated row permutation and index:
transp i max_i p, i+1,
{// the top rows of the matrix remain unchanged:
x!!(0..i-1,0..m-1);
// the pivot row, divided by the pivot element:
{x!(i,l)/x!(i,j) | l=0..m-1};
// subtract suitable multiples of the pivot row:
{{x!(k,l)-x!(k,j)*x!(i,l)/x!(i,j) | k=i+1..n-1; l=0..m-1}}
when
n,m = dim x; max_i, max_x = pivot i (col x j);
x = if max_x>0 then swap x i max_i else x;
end with
pivot i x = foldl max (0,0) [j,abs (x!j)|j=i..#x-1];
max (i,x) (j,y) = if x<y then j,y else i,x;
end;
/* Swap rows i and j of the matrix x. */
swap x i j = x!!(transp i j (0..n-1),0..m-1) when n,m = dim x end;
/* Apply a transposition to a permutation. */
transp i j p = [p!tr k | k=0..#p-1]
with tr k = if k==i then j else if k==j then i else k end;
/* Example: */
let x = dmatrix {2,1,-1,8; -3,-1,2,-11; -2,1,2,-3};
x; gauss_elimination x;
As a language based on
expand = reduce with
(a+b)*c = a*c+b*c;
a*(b+c) = a*b+a*c;
end;
factor = reduce with
a*c+b*c = (a+b)*c;
a*b+a*c = a*(b+c);
end;
expand ((a+b)*2); // yields a*2+b*2
factor (a*2+b*2); // yields (a+b)*2
Calling
"Hello, world!" on the terminal:
extern int puts(char*);
hello = puts "Hello, world!";
hello;
See also
References
- Albert Gräf. "Signal Processing in the Pure Programming Language". Linux Audio Conference 2009.
- Michael Riepe. "Pure – eine einfache funktionale Sprache". Heise.
- "Interview With Albert Gräf". blueparen.
Notes
- ^ Turner, David A. SASL language manual. Tech. rept. CS/75/1. Department of Computational Science, University of St. Andrews 1975.
