Informal Introduction

Unix file is a sequence of bytes.

(0) CHARACTERISTICS

-type specified: sequence

-features: deterministic, non-parameterized

-foreign types: byte, global

(1) SYNTAX

ACCESS-PROGRAMS

(2) CANONICAL TRACES

canonical(T) T = _ n:<int>; p[0]..p[n]:<int>; b[0]..b[n]:<byte>n 0 p[0] 0 p[n] < global::

AUXILIARY FUNCTIONS

errorval: <byte>

errorval() = -1

size: <sequence> <int>

size(s) =

Condition	Value
s = _	0
! s1:<sequence>; p:<int>; b:<byte> [s = s1.PUT(*, p, b) ]	p + 1

get: <sequence> × <int> <byte>

get(seq, pos) =

Condition	Value
pos < 0 pos global::G_sequence_size()	errorval()
size(seq) pos pos < global::G_sequence_size()	global::EOF()
¬( ! s1,s2:<sequence>; b:<byte> [seq = s1.PUT(*, pos, b).s2 ] 0 pos pos < size(seq))	byte::_
! s1,s2:<sequence>; b:<byte> [seq = s1.PUT(*, pos, b).s2 ]	b

(3) SEMANTICS

Legality(PUT((n, T), p, b)) =

Condition	Value
p < 0 p global::G_sequence_size()	%invalid position%
p 0 p < global::G_sequence_size()	%legal%

PUT((n, T) , p, b) =

Condition	Value
! T1,T2:<sequence>; b1:<byte> [T = T1.PUT(*, p, b1).T2 ]	T1.PUT(*, p, b).T2
¬ ! T1,T2:<sequence>; b1:<byte> [T = T1.PUT(*, p, b1).T2 ]	T1.PUT(*, p, b).T2 where T1,T2:<sequence> [T = T1.T2 canonical(T1.PUT(*, p, b).T2)]

Legality(GET(T, p, (n, b))) =

Condition	Value
p < 0 p global::G_sequence_size()	%invalid position%
p 0 p < global::G_sequence_size()	%legal%

GET(T, p, (n, b) ) = get(T, p)

Legality(TRUNC((n, T), p)) =

Condition	Value
p < 0 p global::G_sequence_size()	%invalid position%
p 0 p < global::G_sequence_size()	%legal%

TRUNC((n, T) , p) =

Condition	Value
size(T) p	T
! T1,T2:<sequence>; p1,p2:<int>; b1,b2:<byte>p1 < p p p2 [T = T1.PUT(*, p1, b1).PUT(*, p2, b2).T2 ]	T1.PUT(*, p1, b1).[PUT(*, i, byte::_)]i=p1 + 1..p - 1
T1:<sequence>; p1:<int>; b1:<byte>p p1 [T = PUT(*, p1, b1) ]	_

Legality(SIZE(T)) = %legal%

SIZE(T) = size(T)