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fixed assignment3 pred
[lambda.git]
/
assignment_3_evaluator.mdwn
diff --git
a/assignment_3_evaluator.mdwn
b/assignment_3_evaluator.mdwn
index
9207c05
..
c910064
100644
(file)
--- a/
assignment_3_evaluator.mdwn
+++ b/
assignment_3_evaluator.mdwn
@@
-6,38
+6,40
@@
let true = \x y. x in
let false = \x y. y in
let and = \l r. l (r true false) false in
let make\_pair = \f s g. g f s in
let false = \x y. y in
let and = \l r. l (r true false) false in
let make\_pair = \f s g. g f s in
-let fst = true in
-let snd = false in
+let
get\_
fst = true in
+let
get\_
snd = false in
let empty = make\_pair true junk in
let empty = make\_pair true junk in
-let isempty = \x. x fst in
+let isempty = \x. x
get\_
fst in
let make\_list = \h t. make\_pair false (make\_pair h t) in
let make\_list = \h t. make\_pair false (make\_pair h t) in
-let head = \l. isempty l err (l
snd
fst) in
-let tail = \l. isempty l err (l
snd
snd) in
-
+let head = \l. isempty l err (l
get\_snd get\_
fst) in
+let tail = \l. isempty l err (l
get\_snd get\_
snd) in
+;
; a list of numbers to experiment on
let mylist = make\_list 1 (make\_list 2 (make\_list 3 empty)) in
; a list of numbers to experiment on
let mylist = make\_list 1 (make\_list 2 (make\_list 3 empty)) in
-
+;
; church numerals
let iszero = \n. n (\x. false) true in
let succ = \n s z. s (n s z) in
let mul = \m n s. m (n s) in
; church numerals
let iszero = \n. n (\x. false) true in
let succ = \n s z. s (n s z) in
let mul = \m n s. m (n s) in
-let pred =
\n. iszero n 0 (length (tail (n (\p. make\_list junk p) empty)))
in
+let pred =
(\shift n. n shift (make\_pair 0 0) get\_snd) (\p. p (\x y. make\_pair (succ x) x))
in
let leq = \m n. iszero(n pred m) in
let eq = \m n. and (leq m n)(leq n m) in
let leq = \m n. iszero(n pred m) in
let eq = \m n. and (leq m n)(leq n m) in
-
+;
; a fixed-point combinator for defining recursive functions
let Y = \f. (\h. f (h h)) (\h. f (h h)) in
; a fixed-point combinator for defining recursive functions
let Y = \f. (\h. f (h h)) (\h. f (h h)) in
-
+;
let length = Y (\length l. isempty l 0 (succ (length (tail l)))) in
let length = Y (\length l. isempty l 0 (succ (length (tail l)))) in
-
+;
; synonyms
let makePair = make\_pair in
; synonyms
let makePair = make\_pair in
+let fst = get\_fst in
+let snd = get\_snd in
let nil = empty in
let isNil = isempty in
let makeList = make\_list in
let isZero = iszero in
let mult = mul in
let nil = empty in
let isNil = isempty in
let makeList = make\_list in
let isZero = iszero in
let mult = mul in
-
+;
length (tail mylist)
</textarea>
length (tail mylist)
</textarea>