An Introduction to Functional Programming Through Lambda Calculus

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- 234 -iii) rec DTRAVERSE TEMPTY = []or DTRAVERSE [V,L,R] = APPEND (DTRAVERSE R) (V::(DTRAVERSE L))3)rec EVAL [E1,OP,E2] =let R1 = EVAL E1inlet R2 = EVAL E2inIF STRING_EQUAL OP "+"THEN R1 + R2ELSEIF STRING_EQUAL OP "-"THEN R1 - R2ELSEIF STRING_EQUAL OP "*"THEN R1 * R2ELSE R1 / R2or EVAL N = NChapter 81)i)Normal orderλs.(s s) (λf.λa.(f a) λx.x λy.y) =>(λf.λa.(f a) λx.x λy.y) (λf.λa.(f a) λx.x λy.y) =>(λa.(λx.x a) λy.y) (λf.λa.(f a) λx.x λy.y) =>(λx.x λy.y) (λf.λa.(f a) λx.x λy.y) =>λy.y (λf.λa.(f a) λx.x λy.y) =>λf.λa.(f a) λx.x λy.y =>λa.(λx.x a) λy.y =>λx.x λy.y =>λy.y8 reductionsλf.λa.(f a) λx.x λy.y reduced twiceApplicative orderλs.(s s) (λf.λa.(f a) λx.x λy.y) ->λs.(s s) (λa.(λx.x a) λy.y) ->λs.(s s) (λx.x λy.y) ->λs.(s s) λy.y ->λy.y λy.y ->λy.y5 reductionsλf.λa.(f a) λx.x λy.y reduced onceLazyλs.(s s) (λf.λa.(f a) λx.x λy.y) 1=>(λf.λa.(f a) λx.x λy.y) 1(λf.λa.(f a) λx.x λy.y) 1=>(λa.(λx.x a) λy.y) 2(λa.(λx.x a) λy.y) 2=>(λx.x λy.y) 3(λx.x λy.y) 3=>λy.y λy.y =>
- 235 -λy.y5 reductionsλf.λa.(f a) λx.x λy.y reduced onceii)Normal orderλx.λy.x λx.x (λs.(s s) λs.(s s)) =>λy.λx.x (λs.(s s) λs.(s s)) =>λx.x2 reductionsλs.(s s) λs.(s s) not reducedApplicative orderλx.λy.x λx.x (λs.(s s) λs.(s s)) ->λx.λy.x λx.x (λs.(s s) λs.(s s)) -> ...Non-terminating - 1 reduction/cycleλs.(s s) λs.(s s) reduced every cycleLazyλx.λy.x λx.x (λs.(s s) λs.(s s)) =>λy.λx.x (λs.(s s) λs.(s s)) =>λx.x2 reductions - as normal orderiii)Normal orderλa.(a a) (λf.λs.(f (s s)) λx.x) =>(λf.λs.(f (s s)) λx.x) (λf.λs.(f (s s)) λx.x) =>λs.(λx.x (s s)) (λf.λs.(f (s s)) λx.x) =>λx.x ((λf.λs.(f (s s)) λx.x) (λf.λs.(f (s s)) λx.x)) =>(λf.λs.(f (s s)) λx.x) (λf.λs.(f (s s)) λx.x) => ...Non-terminating - 3 reductions/cycleλf.λs.(f (s s)) λx.x reduced every cycleApplicative orderλa.(a a) (λf.λs.(f (s s)) λx.x) ->λa.(a a) λs.(λx.x (s s)) ->λs.(λx.x (s s)) λs.(λx.x (s s)) ->λx.x (λs.(λx.x (s s)) λs.(λx.x (s s))) ->λs.(λx.x (s s)) λs.(λx.x (s s)) -> ...Non-terminating - 2 reductions/cycleλf.λs.(f (s s)) λx.x reduced before non-terminating cycleLazyλa.(a a) (λf.λs.(f (s s)) λx.x) 1=>(λf.λs.(f (s s)) λx.x) 1(λf.λs.(f (s s)) λx.x) 1=>λs.(λx.x (s s)) λs.(λx.x (s s)) =>λx.x (λs.(λx.x (s s)) λs.(λx.x (s s))) =>λs.(λx.x (s s)) λs.(λx.x (s s)) => ...Non-terminating - 2 reductions/cycleλf.λs.(f (s s)) λx.x reduced before non-terminating cycle
Page 1 and 2:
AN INTRODUCTION TO FUNCTIONAL PROGR
Page 3 and 4:
- 3 -LISP was one of the earliest l
Page 5 and 6:
- 5 -1.4. Execution order in impera
Page 7 and 8:
- 7 -B[1] + B[2] + ... + B[M] + SUM
Page 9 and 10:
- 9 -quantifiers to describe proper
Page 11 and 12:
- 11 -program specification all use
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- 13 -To begin with, we will briefl
Page 15 and 16:
- 15 -Now, compare this with the fo
Page 17 and 18:
- 17 -wherefor example: ::= λx.x
Page 19 and 20:
- 19 -giving:λx.xAn identity opera
Page 21 and 22:
- 21 -λx.xThis is now evaluated as
Page 23 and 24:
- 23 -in the body:λarg.(func arg)g
Page 25 and 26:
- 25 -We can use the self applicati
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- 27 -and body:λsecond.firstWhen a
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- 29 -2.12.3. Making pairs from two
Page 31 and 32:
- 31 -(λx.x λx.x) =>λx.xIt is po
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- 33 -i) the expression is an appli
Page 35 and 36:
- 35 -((λfunc.λarg.(func arg) arg
Page 37 and 38:
- 37 -Bound variablesi) is bound i
Page 39 and 40:
- 39 -i) λx.λy.(λx.y λy.x)ii)
Page 41 and 42:
- 41 -(((cond false) true) x) ==(((
Page 43 and 44:
- 43 -3.5. OROR is a binary operato
Page 45 and 46:
- 45 -two ==(succ one) ==(λn.λs.(
Page 47 and 48:
- 47 -So:def pred = λn.(((cond zer
Page 49 and 50:
- 49 -For example, we could re-writ
Page 51 and 52:
- 51 -4) Show that:λx.(succ (pred
Page 53 and 54:
- 53 -gobble a sweet andgobble a sw
Page 55 and 56:
- 55 -then xelse f (succ x) (pred y
Page 57 and 58:
- 57 -and:-> ... ->will still imply
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- 59 -If this function is now appli
Page 61 and 62:
- 61 -def add1 f x y =if iszero yth
Page 63 and 64:
- 63 -the second minus the first wi
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- 65 -succ (succ (div1 one four)) -
Page 67 and 68:
- 67 -n * n-1 * n-2 * ... * 1in nor
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- 69 -within our intended interpret
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- 71 -Sometimes it may be necessary
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- 73 -λvalue.λs.(s error_type val
Page 75 and 76:
- 75 -def AND X Y =if and (isbool X
Page 77 and 78:
- 77 -def ISBOOL B = MAKE_BOOL (isb
Page 79 and 80:
- 79 -Note that we return NUMB_ERRO
Page 81 and 82:
- 81 -def ’1’ = MAKE_CHAR (succ
Page 83 and 84:
- 83 -will do so. However, for a no
Page 85 and 86:
- 85 -To simplify the presentation
Page 87 and 88:
- 87 -rec 0 = or (SUCC ) = Thus,
Page 89 and 90:
- 89 -def signed_type = ...def SIGN
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- 91 -If the head of a list and the
Page 93 and 94:
- 93 -def MAKE_LIST = make_obj list
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- 95 -LIST_ERRORThe test for an emp
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- 97 -CONS 1 (APPEND (TAIL (CONS 1
Page 99 and 100:
- 99 -For example:1::(2::(3::(4::[]
Page 101 and 102:
- 101 -LIST_EQUAL [] [] = TRUELIST_
Page 103 and 104:
- 103 -In general, the string:" "is
Page 105 and 106:
- 105 -(STRING_LESS (’r’::"ridg
Page 107 and 108:
- 107 -gives value of "" with 10*(1
Page 109 and 110:
- 109 -In general, for:rec =IF IS
Page 111 and 112:
- 111 -Note that this description t
Page 113 and 114:
- 113 -Similarly, to remove a speci
Page 115 and 116:
- 115 -rec DOUBLE [] = []or DOUBLE
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- 117 -"cats"::"dogs"::(λW.(APPEND
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- 119 -‘TAIL ’>6.18. Exercises1
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- 121 -["Betty","Baker"].For exampl
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- 123 -For example:IF STRING_EQUAL
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- 125 -["VDU",25,12]::["modem",20,1
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- 127 -matches the argument:so:[,,]
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- 129 -For example, suppose we have
Page 131 and 132:
- 131 -to place the Nth item, skip
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- 133 -[7,EMPTY,EMPTY]To add 4 to t
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- 135 -[3,EMPTY,EMPTY],[5,EMPTY,[6,
Page 137 and 138:
- 137 -TFIND 5 [4,[3,EMPTY,EMPTY],[
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- 139 -7.14. Binary tree efficiency
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- 141 -λ[a,b].(SUM_SQ2 a b)so:def
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- 143 -and so on.def istype (t::o)=
Page 145 and 146:
- 145 - ::= ( + ) |( + ) |( + ) |(
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- 147 -IF ISZERO (ADD 1 2)THEN 1ELS
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- 149 -cond one (add (succ one) (pr
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- 151 -λdummy.e2Instead, we have t
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- 153 -The first Church-Rosser theo
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- 155 -(λx.x λy.y) 2=>λy.yand th
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- 157 -For example, consider:SQUARE
Page 159 and 160:
- 159 -SQUARE 1 => ... =>IFIND 1 SQ
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- 161 - : For objects which do not
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- 163 -is a tuple consisting of two
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- 165 -to indicate both integer and
Page 167 and 168:
- 167 -- tl;> fn : (’a list) -> (
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- 169 -Functions have the form:fn
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- 171 -For example, to find the lar
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- 173 -9.19. Pattern matchingSML fu
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- 175 -end;> val sort = fn : (int l
Page 177 and 178:
- 177 -- fun length [] = 0 |length
Page 179 and 180:
- 179 -- datatype traffic_light = r
Page 181 and 182:
- 181 -but this defines the new typ
Page 183 and 184: - 183 -con empty = empty : (’a tr
Page 185 and 186: - 185 -iv)Join strings s1 and s2 to
Page 187 and 188: - 187 -( + )( - )( * )( / ) == numb
Page 189 and 190: - 189 -10.4. Logictis the primitive
Page 191 and 192: - 191 -(> 9 8 7 6 5) ->tThe primiti
Page 193 and 194: - 193 -It is important to note that
Page 195 and 196: - 195 -nilwhich may be also written
Page 197 and 198: - 197 -(car ’(1 2 3)) ->1(cdr ’
Page 199 and 200: - 199 -(tadd 7 nil) ->(7 nil nil)(t
Page 201 and 202: - 201 -For example, suppose the ave
Page 203 and 204: - 203 -10.17. Symbols, quoting and
Page 205 and 206: - 205 -Note once again that there m
Page 207 and 208: - 207 -iv) find the sum of applying
Page 209 and 210: - 209 -ii) Write a function which i
Page 211 and 212: - 211 -Chapter 3 - Conditions, bool
Page 213 and 214: - 213 -11. R. M. Burstall, J. S. Co
Page 215 and 216: - 215 -55. P. Wegner, Programming L
Page 217 and 218: - 217 - - (g h) - - g - - h - f
Page 219 and 220: - 219 -λb.b3)i) a) (identity ) =>
Page 221 and 222: - 221 -λb.(λa.{a} b))λa.{a}a fre
Page 223 and 224: - 223 -not (or false false) => ...
Page 225 and 226: - 225 -false (implies false true) f
Page 227 and 228: - 227 -then fun nelse add (fun n) (
Page 229 and 230: - 229 -i) ISBOOL 3 => ... =>MAKE_BO
Page 231 and 232: - 231 -iii)def SIGN_+ X Y =if and (
Page 233: - 233 -THEN [H,M,S]ELSElet M = M +
Page 237 and 238: - 237 -gconstr (v:int) ((h::t):int
Page 239 and 240: - 239 -0(+ n (nsum (- n 1)))))ii) (
Page 241: - 241 -(if (= m1 m2)(if (< s1 s2)tn
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An Introduction to Functional Programming Through Lambda Calculus

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