P′′

P′′

Paradigm	Imperative, structured
Designed by	Corrado Böhm
First appeared	1964
Typing discipline	untyped
Dialects
Brainfuck
Influenced
Brainfuck

P′′ is a primitive computer programming language created by Corrado Böhm in 1964 to describe a family of Turing machines.

${\displaystyle {\mathcal {P}}^{\prime \prime }}$ (hereafter written P′′) is formally defined as a set of words on the four-instruction alphabet {R, λ, (, )}, as follows:

Böhm gives the following program to compute the predecessor (x-1) of an integer x > 0:

which translates directly to the equivalent brainfuck program:

The program expects an integer to be represented in bijective base-n notation, with a₁, ..., a_n coding the digits 1,...,n, respectively, and to have an a₀ before and after the digit-string. (E.g. in bijective base-2, the number eight would be encoded as a₀a₁a₁a₂a₀, because 8 = 1*2² + 1*2¹ + 2*2⁰.) At the beginning and end of the computation, the tape-head is on the a₀ preceding the digit-string.

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