4.7.2 TC-E Samples

This example demonstrates the computation and display of escaping variables (and formal arguments). By default, all the variables must be considered as escaping, since it is safe to put a non escaping variable onto the stack, while the converse is unsafe.

let
  var one := 1
  var two := 2
  function incr(x: int) : int = x + one
in
  incr(two)
end

$ tc -XEAeEA variable-escapes.tig
/* == Abstract Syntax Tree. == */

function _main() =
  (
    let
      var /* escaping */ one := 1
      var /* escaping */ two := 2
      function incr(/* escaping */ x : int) : int =
        (x + one)
    in
      incr(two)
    end;
    ()
  )
/* == Abstract Syntax Tree. == */

function _main() =
  (
    let
      var /* escaping */ one := 1
      var two := 2
      function incr(x : int) : int =
        (x + one)
    in
      incr(two)
    end;
    ()
  )

Compute the escapes after binding, so that the AST is known to be sane enough (type checking is irrelevant): the EscapeVisitor should not bother with undeclared entities.

undeclared

$ tc -e undefined-variable.tig
error→undefined-variable.tig:1.1-10: undeclared variable: undeclared
⇒4

Run your compiler on merge.tig and to study its output. There is a number of silly mistakes that people usually make on TC-E: they are all easy to defeat when you do have a reasonable test suite, and once you understood that torturing your project is a good thing to do.