From: Jim Pryor <profjim@jimpryor.net>
Date: Sun, 21 Nov 2010 22:45:24 +0000 (-0500)
Subject: week9 tweak
X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=8ff8ea492898be6cbb5fa1a237cbcf91471a7cee;ds=sidebyside

week9 tweak

Signed-off-by: Jim Pryor <profjim@jimpryor.net>
---

diff --git a/week9.mdwn b/week9.mdwn
index 3f0911ab..19041582 100644
--- a/week9.mdwn
+++ b/week9.mdwn
@@ -500,62 +500,73 @@ To get the whole process started, the complex computation so defined will need t
 
 -- FIXME --
 
-    [H] ; *** aliasing ***
-        let y be 2 in
-          let x be y in
-            let w alias y in
-              (y, x, w)           ==> (2, 2, 2)
-
-    [I] ; mutation plus aliasing
-        let y be 2 in
-          let x be y in
-            let w alias y in
-              change y to 3 then
-                (y, x, w)         ==> (3, 2, 3)
-
-    [J] let f be (lambda (y) -> BODY) in  ; a
-          ... f (EXPRESSION) ...
-
-        (lambda (y) -> BODY) EXPRESSION
-
-        let y be EXPRESSION in            ; b
-          ... BODY ...
-
-    [K] ; *** passing "by reference" ***
-        let f be (lambda (alias w) ->     ; ?
-          BODY
-        ) in
-          ... f (y) ...
-
-        let w alias y in                  ; d
-          ... BODY ...
-
-    [L] let f be (lambda (alias w) ->
-          change w to 2 then
-            w + 2
-        ) in
-          let y be 1 in
-            let z be f (y) in
-              ; y is now 2, not 1
-              (z, y)              ==> (4, 2)
-
-    [M] ; hyper-evaluativity
-        let h be 1 in
-          let p be 1 in
-            let f be (lambda (alias x, alias y) ->
-              ; contrast here: "let z be x + y + 1"
-              change y to y + 1 then
-                let z be x + y in
-                  change y to y - 1 then
-                    z
-            ) in
-              (f (h, p), f (h, h))
-                                  ==> (3, 4)
-
-    Notice: h, p have same value (1), but f (h, p) and f (h, h) differ
-
-
-Fine and Pryor on "coordinated contents" (see, e.g., [Hyper-Evaluativity](http://www.jimpryor.net/research/papers/Hyper-Evaluativity.txt))
+	[H] ; *** aliasing ***
+	    let y be 2 in
+	      let x be y in
+	        let w alias y in
+	          (y, x, w)
+								; evaluates to (2, 2, 2)
+
+	[I] ; mutation plus aliasing
+	    let y be 2 in
+	      let x be y in
+	        let w alias y in
+	          change y to 3 then
+	            (y, x, w)
+								; evaluates to (3, 2, 3)
+
+	[J] ; as we already know, these are all equivalent:
+	
+	    let f be (lambda (y) -> BODY) in  ; #1
+	      ... f (EXPRESSION) ...
+	
+	    (lambda (y) -> BODY) EXPRESSION   ; #2
+	
+	    let y be EXPRESSION in            ; #3
+	      ... BODY ...
+
+	[K] ; *** passing by reference ***
+	    ; now think: "[J#1] is to [J#3] as [K#1] is to [K#2]"
+	
+	    ?                                 ; #1
+	
+	    let w alias y in                  ; #2
+	      ... BODY ...
+	
+	    ; We introduce a special syntactic form to supply
+	    ; the missing ?
+	
+	    let f be (lambda (alias w) ->     ; #1
+	      BODY
+	    ) in
+	      ... f (y) ...
+
+	[L] let f be (lambda (alias w) ->
+	      change w to 2 then
+	        w + 2
+	    ) in
+	      let y be 1 in
+	        let z be f (y) in
+	          ; y is now 2, not 1
+	          (z, y)
+								; evaluates to (4, 2)
+
+	[M] ; hyper-evaluativity
+	    let h be 1 in
+	      let p be 1 in
+	        let f be (lambda (alias x, alias y) ->
+	          ; contrast here: "let z be x + y + 1"
+	          change y to y + 1 then
+	            let z be x + y in
+	              change y to y - 1 then
+	                z
+	        ) in
+	          (f (h, p), f (h, h))
+								; evaluates to (3, 4)
+
+Notice: in [M], `h` and `p` have same value (1), but `f (h, p)` and `f (h, h)` differ.
+
+See Pryor's "[Hyper-Evaluativity](http://www.jimpryor.net/research/papers/Hyper-Evaluativity.txt)".
 
 
 ##Four grades of mutation involvement##