NIAL Nested Interactive Array Language Dennis Brown Northern Kentucky University CSC 507 – November 2005

Origins of NIAL Based on nested array theory developed by Dr. Trenchard More, Jr. Invented in 1981 by Michael Jenkins of Queen’s University in Kingston, Ontario Influenced by APL and Lisp NIAL is an acronym for Nested Interactive Array Language, but is also a reference to Njal’s Saga (a Nordic legend)

APL vs. NIAL APL was invented in 1962 Very efficient for some types of calculation, but required a special character set:

APL vs. NIAL (cont.) NIAL uses keywords instead of symbols, so no custom keyboard is required –For example, ρ (rho) in APL becomes “reshape” in NIAL NIAL also adds control structures (from imperative languages) that APL did not have The original version of APL did not support nested arrays

NIAL Data Types Numbers –integers –floating points –booleans (l, o, True, False) Characters –`X, `v, `3 Lists –3 `C 5 (strand notation) –[3 `C 5] –[] (empty list) Strings –‘abc’ –`a `b `c Phrases –“dog –phrase ‘dog’ Faults –‘?conform’

Strings vs. Phrases A string is a list: first ‘abc’  `alast ‘abc’  `c A phrase is atomic: first “abc  “abclast “abc  “abc

Lists – Examples sum – 9 sum [2 3 4] –[2 3 4] sum (2 3 4) (1 2 3) –3 5 7 each sum (2 3 4) (1 2 3) –9 6 x y z := –assigns 5 to x, 6 to y, 7 to z [1 2 3] * 2 –[2 4 6] [1 2 3] * [3 2 1] –[3 4 3] [1 2 3] * –[3 6 9] [2 4 6] [1 2 3]

Lisp vs. NIAL (car 1 2 3) 1 (cdr 1 2 3) (2 3) (cons 1 (2 3)) (1 2 3) first rest hitch 1 (2 3) 1 2 3

Tables A table is a multi-dimensional list The reshape function can be used to create a table with a specified number of rows and columns 2 3 reshape reshape

Tables – Continued x := 3 3 reshape count x | [2,] (row slice) x | [,2] (col. slice) (1 2) 6 post

Functions Functions are defined using the syntax “is operation,” followed by the formal parameters, and then the function body enclosed in braces Functions are evaluated using right associativity Examples: factorial IS OPERATION x { * count x } nthroot IS OPERATION x n { power x ( reciprocal n ) }

Transformers A transformer changes how functions are applied “each” is a built-in transformer that applies a function to each value of a list each first (“abc “def) (3 7 8) (`z `x `q) –“abc 3 `z New transformers can be created using IS TRANSFORMER Transformers were a novel feature in NIAL, and allow the language to support parallel architectures efficiently

Atlases An atlas is a list of functions that can be applied to a data item, producing a list of results [first, last, reverse] `a `b `c –[`a `c ‘cba’] brackets are used because ‘cba’ is a list! [+, -, *, /, quotient] 12 7 –

Different Ways of Saying the Same Thing x := ‘aeiou’ x := True x := x gets 3 * 4 * 5 (0 3) x := `a `e `i `o `u x := l x gets 3 plus 4 x gets plus 3 4 x := 3 times prod 4 5 [0 3] choose x x | [0, 3]

IF Statements IF, ELSE, ELSEIF, and ENDIF are supported Comparison operators and boolean operations are available IF (x >= 3.4) and (y < 7) THEN out_of_range := True ELSE out_of_range := False ENDIF

CASE Statements CASE statements allow selection based on a value (not necessarily an integer) An optional ELSE clause handles the default case Each non-default case must end with END – there is no fall-through like in C and Java CASE n FROM 1: value := ‘one’ END 2: value := ‘two’ END ELSE value := ‘unknown’ ENDCASE

Loops NIAL supports the three usual types of loops: –WHILE {condition} DO {expressions} ENDWHILE –REPEAT {expressions} UNTIL {condition} ENDREPEAT –FOR {variable} WITH {range} DO {expressions} ENDFOR The count function is useful with FOR loops –FOR i WITH count 10 DO write(i) ENDFOR It is better to use the EACH transformer, however The EXIT statement can be used to force a loop to terminate

Q’Nial Interpreter Q’Nial allows NIAL statements to be entered and interpreted dynamically Windows version is now available free from NIAL Systems ( C++ source code for Q’Nial is also available free of charge

Q’Nial in Action

The Future of NIAL NIAL has been used in academic research (particularly in AI) and at some insurance companies, but has declined in popularity since the 1980s Newer languages in its niche can do the same tasks just as well or better –APL version 2 –J and its successors J is available for free; NIAL was very expensive until recently NIAL is not easy to integrate with native C libraries Best use of NIAL is as a prototyping language

References Nial Systems Limited Q’nial Research Project “A Quick Look at Nial,” Journal of J/APL Comparison of array languages, Keith Smillie “APL programming language,” Wikipedia

Questions?