PAL---a language designed for teaching programming linguistics

Protection in programming languages

“…The first language to allow procedures to be passed about was LISP, with its FUNARG lists [6]. Later languages, ISWIM [5], PAL [2], and GEDANKEN [7], also have such procedures and have the execute-only restriction (LISP does not). Our example programs will be written in GEDANKEN as its definition is probably the most readily accessible to the reader.…”

“…Furthermore, by (2), any user of the primitive functions will not be able to examine the objects except through the functions provided.…”

Simple LR(k) grammars

“…They have been compared with a similar system based on the mixed strategy precedence (MSP) technique of McKeeman [12]. The MSP and SLR(1) systems were used to generate parsers for the languages XPL [12], SPL [15], EULER [14], ALGOL 60 [13], and PAL [16]. Here at ucsc, the SLR(1) system generated parsers in from one-twentieth to one-tenth the time required by the MSP system.…”

Some examples of the use of function-producing functions

“…a I g(f(h x)(h y))(zip a g f (t x)(t y)); def pair x y = x,y; def hums = (1,2,3,4,5); def zips ffi zip () prefix pair zips nums (reverse nums); ((1,5), (2,4), (3,3),(4,2),(5,1)) def sproduet = zip 0 plus mult; def map2 f x y = let g z = map(f z)y; concat (map g x); def cproduct = map2 pair; cproduct (1,2,3)(4,5,6); Functions for analyzing strings of characters may be constructed systematically by defining a set of functions for analyzing called 'parsers' and then by defining functions which create parsers from other parsers.…”