nLab
proofs as programs

natural deduction metalanguage, practical foundations

type theory (dependent, intensional, observational type theory, homotopy type theory)

logic	category theory	type theory
true	terminal object/(-2)-truncated object	h-level 0-type/unit type
false	initial object	empty type
proposition	(-1)-truncated object	h-level 1-type/h-prop
proof	generalized element	program
conjunction	product	product type
disjunction	coproduct ((-1)-truncation of)	sum type (bracket type of)
implication	internal hom	function type
negation	internal hom into initial object	function type into empty type
universal quantification	dependent product	dependent product type
existential quantification	dependent sum ((-1)-truncation of)	dependent sum type (bracket type of)
equivalence	path space object	identity type
equivalence class	quotient	quotient type
induction	colimit	inductive type, W-type, M-type
higher induction	higher colimit	higher inductive type
completely presented set	discrete object/0-truncated object	h-level 2-type/preset/h-set
set	internal 0-groupoid	Bishop set/setoid
universe	object classifier	type of types
modality	closure operator monad	modal type theory, monad (in computer science)

Idea

In type theory, regarding propositions as types, a proof of a proposition is given by constructing a term of the corresponding type. This can hence be regarded as a program to compute a specific term (output).

An exposition is in

That Martin-Löf dependent type theory can be regarded also as a functional programming language by identifying proofs as programs was stressed in

Per Martin-Löf, Constructive mathematics and computer programming, Philosophical Transactions of the Royal Society of London (Series A) 312 (1984), no. 1522, pp. 501–518.

Revised on September 5, 2012 17:33:06 by Urs Schreiber (131.174.191.191)