THE ALGOL FAMILY AND ML

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Horatio Johnston
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1 THE ALGOL FAMILY AND ML

2 Lisp Algl 60 Algl 68 Pascal ML Mdula Haskell Many ther languages: Algl 58, Algl W, Euclid, EL1, Mesa (PARC), Mdula-2, Obern, Mdula-3 (DEC)

! Basic Language f 1960! Simple imperative language + functins! Successful syntax, BNF -- used by many successrs! statement riented! begin end blcks (like C { } )! if then else!

3 ! Basic Language f 1960! Simple imperative language + functins! Successful syntax, BNF -- used by many successrs! statement riented! begin end blcks (like C { } )! if then else! Recursive functins and stack strage allcatin! Fewer ad hc restrictins than Frtran! General array references: A[ x + B[3]*y]! Type discipline was imprved by later languages! Very influential but nt widely used in US! Tny Hare: Here is a language s far ahead f its time that it was nt nly an imprvement n its predecessrs but als n nearly all f its successrs.

4 real prcedure average(a,n); real array A; integer n; begin real sum; sum := 0; fr i = 1 step 1 until n d sum := sum + A[i]; average := sum/n end; n ; here set prcedure return value by assignment

5 ! Questin: Is x := x equivalent t ding nthing?! Interesting answer in Algl integer prcedure p; begin. p := p. end; Assignment here is actually a recursive call

6 ! Hles in type discipline Parameter types can be arrays, but " N array bunds Parameter types can be prcedures, but " N argument r return types fr prcedure parameters! Prblems with parameter passing mechanisms Pass-by-name lazy evaluatin Pass-by-value expensive fr arrays! Sme awkward cntrl issues gt ut f blck requires memry management

! Cnsidered difficult t understand Idisyncratic terminlgy " Types were called mdes " Arrays were called multiple values Used vw grammars instead f BNF "

7 ! Cnsidered difficult t understand Idisyncratic terminlgy " Types were called mdes " Arrays were called multiple values Used vw grammars instead f BNF " Cntext-sensitive grammar invented by van Wijngaarden Elabrate type system Cmplicated type cnversins! Fixed sme prblems f Algl 60 Eliminated pass-by-name! Nt widely adpted

8 ! Primitive mdes int real char bl string cmpl (cmplex) bits bytes sema (semaphre) frmat (I/O) file # Cmpund mdes # arrays # structures # prcedures # sets # pinters Rich, structured, and rthgnal type system is a majr cntributin f Algl 68.

9 ! Strage management Lcal strage n stack Heap strage, explicit allc, and garbage cllectin! Parameter passing Pass-by-value Use pinter types t btain pass-by-reference! Assignable prcedure variables Fllw rthgnality principle rigrusly

variants, subranges Mre restrictive than Algl 60/68 " Prcedure

10 ! Designed by Niklaus Wirth (Turing Award)! Revised the type system f Algl Gd data-structuring cncepts " recrds, variants, subranges Mre restrictive than Algl 60/68 " Prcedure parameters cannt have prcedure parameters! Ppular teaching language! Simple ne-pass cmpiler Niklaus Wirth

11 ! Array bunds part f type prcedure p(a : array [1..10] f integer) prcedure p(n: integer, a : array [1..n] f integer) Attempt at rthgnal design backfires Parameter must be given a type Type cannt cntain variables # Nt successful fr industrial-strength prjects # Kernighan: Why Pascal is nt my favrite language

12 Designed by Dennis Ritchie, Turing Award winner, fr writing Unix! Evlved frm B, which was based n BCPL B was an untyped language; C adds sme checking! Relatinship between arrays and pinters An array is treated as a pinter t first element Pinter arithmetic is nt cmmn in ther languages! Ritchie qute C is quirky, flawed, and a tremendus success.

Cmbinatin f Lisp and Algl-like features Expressin-riented Higher-rder functins

13 ! Statically typed, general-purpse prgramming language! Type safe!! Intended fr interactive use! Cmbinatin f Lisp and Algl-like features Expressin-riented Higher-rder functins Garbage cllectin Abstract data types Mdule system Exceptins! Designed by Turing-Award winner Rbin Milner fr LCF therem prver! Used in textbk as example language

! Haskell is a prgramming language that is

higher-rder, functinal, supprts type inference,

frm ML: lazy evaluatin, purely functinal,

! Designed by cmmittee in 80 s and 90 s t unify

14 ! Haskell is a prgramming language that is Similar t ML: general-purpse, strngly typed, higher-rder, functinal, supprts type inference, supprts interactive and cmpiled use Different frm ML: lazy evaluatin, purely functinal, rapidly evlving type system.! Designed by cmmittee in 80 s and 90 s t unify research effrts in lazy languages. Haskell 1.0 in 1990, Haskell 98, Haskell nging. A histry f Haskell: Being lazy with class HOPL 3 Paul Hudak Simn Peytn Jnes Jhn Hughes Phil Wadler

15 ! Gd vehicle fr studying language cncepts Types and type checking " General issues in static and dynamic typing " Type inference " Plymrphism and generic prgramming Cntrl " Retentin

16 ! Functinal prgramming will make yu think differently abut prgramming. Mainstream languages are all abut state Functinal prgramming is all abut values! Ideas will make yu a better prgrammer in whatever language yu regularly use.! A lt f current research is dne in the cntext f Functinal Prgramming.

- Replacement of a single statement with a sequence of statements(promotes regularity)

- Replacement of a single statement with a sequence of statements(promotes regularity) ALGOL - Java and C built using ALGOL 60 - Simple and cncise and elegance - Universal - Clse as pssible t mathematical ntatin - Language can describe the algrithms - Mechanically translatable t machine