mike dupont
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" TMC (Tail Modulo Cons) is a code transformation that\n rewrites transformed functions in destination-passing-style, in\n such a way that certain calls that were not in tail position in the\n original program become tail-calls in the transformed program.\n\n As a classic example, the following program\n {|\n let[@tail_mod_cons] rec map f = function\n | [] -> []\n | x :: xs ->\n let y = f x in\n y :: map f xs\n |}\n becomes (expressed in almost-source-form; the translation is in\n fact at the Lambda-level)\n {|\n let rec map f = function\n | [] -> []\n | x :: xs ->\n let y = f x in\n let dst = y :: Placeholder in\n map_dps dst 1 f xs; dst\n and map_dps dst offset f = function\n | [] ->\n dst.offset <- []\n | x :: xs ->\n let y = f x in\n let dst' = y :: Placeholder in\n dst.offset <- dst';\n map_dps dst 1 f fx\n |}\n\n In this example, the expression (y :: map f xs) had a call in\n non-tail-position, and it gets rewritten into tail-calls. TMC\n handles all such cases where the continuation of the call\n (what needs to be done after the return) is a \"construction\", the\n creation of a (possibly nested) data block.\n\n The code transformation generates two versions of the\n input function, the \"direct\" version with the same type and\n behavior as the original one (here just [map]), and\n the \"destination-passing-style\" version (here [map_dps]).\n\n Any call to the original function from outside the let..rec\n declaration gets transformed into a call into the direct version,\n which will itself call the destination-passing-style versions on\n recursive calls that may benefit from it (they are in tail-position\n modulo constructors).\n\n Because of this inherent code duplication, the transformation may\n not always improve performance. In this implementation, TMC is\n opt-in, we only transform functions that the user has annotated\n with an attribute to request the transformation.\n",
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