fun/interpreter.bruijn

# originally written in obfuscated form by John Tromp for IOCCC 2012
# run with `printf 000010 | bruijn interpreter.bruijn`
# note that Tromp's IO uses an additional abstraction at the beginning ("00" ++ ...)

:import std/Combinator .
:import std/Number/Binary .
:import std/List .

uni [0 0] int [0 Ω] ⧗ (List Bit) → Term
	int [[[0 go (2 2) 1]]]
		go [[[[2 match]]]]
			match [4 case-0 case-1]
				case-0 2 exp
					exp [1 case-00 case-01]
						case-00 2 abs
							abs [[2 [0 1 2]]]
						case-01 3 [3 app]
							app [2 0 (1 0)]
				case-1 0 case-10 case-11
					case-10 1 cont
						cont [0 1]
					case-11 [3 [3 var] 4]
						var [1 (0 3)]

str→blc map (c ∘ lsb)

:test (str→blc "0010") ([[1]] : ([[1]] : ([[0]] : {}[[1]])))

exec uni ∘ str→blc

:test (exec "0011") ([0])
:test (exec "001111") ([0])
:test (exec "000010") ([0])
:test (exec "00000001110011100111010") ((+3u))
:test (exec "0001010000000001011111011001011110110100000011100111001110100000011100111001110011100111010") ((+8u))
:test (exec "00010000010101110000001100111000000101111011001110100011000100000011100111001110011100111010") ((+120u))
:test (exec "000101010100010001110000101110110100001110000101110110100000000001011000000001010111111110111111001011111110111110111011011001000000010111101011000000001011011101100000100001011000000001110011001100110011001110011100110111000010110000000011001110011001100110011100111001101110000101100000000111001110011001100110011100111001101110000010") ("cba")

main exec