Vault's Syntax at a Glance

Many programmers find it tedious to learn a language's syntax from a formal grammar. This web page provides a quick reference to Vault's syntax by providing a single example of every major construct in the language. Since Vault statements and expressions are familiar from C, the code below has few examples of these. (Hovering the mouse over a syntactic element will provide information about that element.) For a more complete reference, we also have a formal grammar.

extern module Region : extern REGION;

interface SampleIntf {
  type color;
  type stack<$T>;
  type length = int;
  length size<$T>(stack<$T>);
  float const pi;
  struct point { int x,y; };
  point? cursor;
}

module SampleMod : SampleIntf {
  type color = (int,int,int);
  variant stack<$T> [ `Empty | `Node($T,stack<$T>) ];
  type length = int;
  length size<$T>(stack<$T> stk) {
    switch (stk) {
      case `Empty: return 0;
      case `Node(_,stk2): return 1 + size(stk2);
    }
  }
  float const pi = 3.14159;
  module Inner { int const ZERO = 0; }
  struct point { int x,y; };
  point? cursor = new point {x=Inner.ZERO; y=Inner.ZERO;};
  int privatefun<$L:key>(tracked($R) region rgn, {$R}:int[$L] array, tracked($L) int len) [-$R] {
    int average($Q:int[$L] arr) [$Q] {
      int sum = 0;
      for (int i=0; i<arr.length; i++)
        sum += arr[i];
      return sum / arr.length;
    }
    int avg = average(array);
    Region.delete(rgn);
    return avg;
  }
}