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*To*: address@hidden*Subject*: Re: CPS in Parrot*From*: Dave Long <address@hidden>*Date*: Sat, 09 Aug 2003 14:56:52 -0700*Sender*: address@hidden

> Dan is right when he says that we shouldn't think of them as > plain functions and Scheme may have made a mistake there. A contributing factor* (from a symmetry view) may be the REPL orientation, which leads to thinking of Expressions being evaluated to produce Values, but if one takes Continuations as dual to Values, then: Values (1->A) are what they are, and can be passed to a Function (A->B) to yield a new Value (1->B), or handed off to a Continuation (A->0) of the right shape. Functions can act on Values, as above, and on Continuations, as below, and can also be composed directly, from (Z->A) and (A->B) to (Z->B). Continuations (A->0) are what they are, and can be composed with a Function (Z->A) to yield a new Continuation (Z->0), or passed a Value (1->A) of the right shape. Andrzej Filinski, Declarative Continuations and Categorical Duality <http://citeseer.nj.nec.com/filinski89declarative.html> Think of a spreadsheet: one enters data into the cells (values), selects output formats for the cells (continuations), and puts formulae in between (functions). For each intermediate cell, cells which refer to it look like continuations, and cells to which it refers, like values. -Dave :: :: :: * I recall at least one early AIM which recognized Hewitt's actors as being in a looking glass world, so the symmetry isn't completely hidden by REPLing. Landin makes sure to note that an ISWIM program-point definition introduces a "deviant" kind of function, not a plain one.

**Follow-Ups**:**Re: CPS in Parrot***From:*Matthias Felleisen <matthias@ccs.neu.edu>

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