Here are the definitions pre-loaded for working on assignment 3:
-<textarea id="INPUT" style="border: 2px solid black; color: black; font-family:
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- ; booleans
- 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 fst = true in
- let snd = false in
- let empty = make_pair true junk in
- let isempty = \x. x fst 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
-
- ; 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
- let pred = \n. iszero n 0 (length (tail (n (\p. make_list junk p) empty))) 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
-
- let length = Y (\length l. isempty l 0 (succ (length (tail l)))) in
-
- ; synonyms
- let makePair = make_pair 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 id="INPUT" style="border: 2px solid black; color: black; font-family: monospace; height: 3in; overflow: auto; padding: 0.5em; width: 100%;">
+; booleans
+let true = \x y. x in
+let false = \x y. y in
+let and = \l r. l (r true false) false in
+let or = \l r. l true r in
+;
+let make\_pair = \f s g. g f s in
+let get\_fst = true in
+let get\_snd = false in
+let empty = make\_pair true junk in
+let isempty = \x. x get\_fst in
+let make\_list = \h t. make\_pair false (make\_pair h t) 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
+;
+; church numerals
+let iszero = \n. n (\x. false) true in
+let succ = \n s z. s (n s z) in
+let add = \l r. l succ r in
+let mul = \m n s. m (n s) 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
+;
+; 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 fold = Y (\f l g z. isempty l z (g (head l)(f (tail l) g z))) 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 t1 = (make\_list 1 empty) in
+let t2 = (make\_list 2 empty) in
+let t3 = (make\_list 3 empty) in
+let t12 = (make\_list t1 (make\_list t2 empty)) in
+let t23 = (make\_list t2 (make\_list t3 empty)) in
+let ta = (make\_list t1 t23) in
+let tb = (make\_list t12 (make\_list t3 empty)) in
+let tc = (make\_list t1 (make\_list t23 empty)) in
+;
+;sum-leaves t1 ; ~~> 1
+;sum-leaves t2 ; ~~> 2
+;sum-leaves t3 ; ~~> 3
+;sum-leaves t12 ; ~~> 3
+;sum-leaves t23 ; ~~> 5
+;sum-leaves ta ; ~~> 6
+;sum-leaves tb ; ~~> 6
+;sum-leaves tc ; ~~> 6
+;
+; updated: added add, and fold for v1 lists; and defn of tb fixed
+; hint:
+fold mylist add 0
</textarea>
+
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<input id="ETA" type="checkbox">do eta-reductions too
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