<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Jul 11, 2012, at 3:52 PM, Ryan Newton wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; font-family: 'Lucida Grande'; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; ">So would this mean using a marking approach like David's example?  Or simply pick an evaluation order, but provide a mechanism to proceed if the desired redex is stuck (e.g. a blocked 'get' waiting for communication)?</span></blockquote></div><br><div><br></div><div>short: Redex book chapter 1</div><div><br></div><div>long: eval is the semantics, |--> is the machine, --> is an "algebraic" system. Both specify eval, independently. The "naive" view is that |---> "fixes" an evaluation order, and that was debunked with Plotkin's 1972 paper. In general, people are happy with a |--> specification, because a calculus is too far away from machine thinking, which is what PL people prefer. |--> does not have to be a 'sequential' [Milner 1971] transition function. </div><div><br></div><div>for the mathematical spec, you don't need markings. That's just for machine processing. I have never seen it used (or would bother to use it) in a pencil-and-paper model. </div><div><br></div><div>Helps? -- Matthias</div><div><br></div></body></html>