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Lustre (programming language) - Wikiwand

Lustre is a formally defined, declarative, and synchronous dataflow programming language for programming reactive systems. It began as a research project in the early 1980s. A formal presentation of the language can be found in the 1991 Proceedings of the IEEE.[1] In 1993 it progressed to practical, industrial use in a commercial product as the core language of the industrial environment SCADE, developed by Esterel Technologies. It is now used for critical control software in aircraft,[2] helicopters, and nuclear power plants.

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A Lustre program is a series of node definitions, written as:

node foo(a : bool) returns (b : bool);
let
  b = not a;
tel

Where foo is the name of the node, a is the name of the single input of this node and b is the name of the single output. In this example the node foo returns the negation of its input a, which is the expected result.

Inner variables

Additional internal variables can be declared as follows: 

node Nand(X,Y: bool) returns (Z: bool);
  var U: bool;
let
  U = X and Y;
  Z = not U;
tel

Note: The equations order doesn't matter, the order of lines U = X and Y; and Z = not U; doesn't change the result.

Special operators

pre pReturns the previous value of p
p -> qSet p as the initial value of the expression q

Edge detection

node Edge (X : bool) returns (E : bool);
let
  E = false -> X and not pre X;
tel