## Mangarevan Counting

### June 20, 2017

Here are our conversion functions:

```(define (integer->mangareva n)
(when (not (<= 1 n 799))
(error 'integer->mangareva "out of range"))
(let loop ((n n) (m (list)))
(cond ((<= 80 n) (loop (remainder n 80)
(cons "V" (cons (number->string (quotient n 80)) m))))
((<= 40 n) (loop (- n 40) (cons "T" m)))
((<= 20 n) (loop (- n 20) (cons "P" m)))
((<= 10 n) (loop (- n 10) (cons "K" m)))
((<= 1  n) (loop 0 (cons (number->string n) m)))
(else (apply string-append (reverse m))))))```
```(define (mangareva->integer str)
(define (digit? c) (char<=? #\1 c #\9))
(let loop ((cs (string->list str)) (n 0))
(list-match cs
(() n)
((m) (digit? m) (loop '() (+ n (char->integer m) -48)))
((#\K . rest) (loop rest (+ n 10)))
((#\P . rest) (loop rest (+ n 20)))
((#\T . rest) (loop rest (+ n 40)))
((m #\V . rest) (digit? m)
(loop rest (+ n (* (- (char->integer m) 48) 80))))
(else (error 'mangareva->integer "not a number")))))```

We used pattern matching for the conversion from Mangarevan to integer, because it’s much easier to read than parsing each element of the number. Note that our error checking is not sufficient to find all mis-formed Mangarevan numbers. It’s easy to do an exhaustive test:

```> (do ((n 1 (+ n 1))) ((= n 800))
(assert (mangareva->integer (integer->mangareva n)) n))```

That writes nothing, on the theory that no news is good news. Here’s a complete list of Mangarevan counting numbers:

```> (map integer->mangareva (range 1 800))
("1" "2" "3" "4" "5" "6" "7" "8" "9" "K" "K1" "K2" "K3" "K4"
"K5" "K6" "K7" "K8" "K9" "P" "P1" "P2" "P3" "P4" "P5" "P6"
"P7" "P8" "P9" "PK" "PK1" "PK2" "PK3" "PK4" "PK5" "PK6"
"PK7" "PK8" "PK9" "T" "T1" "T2" "T3" "T4" "T5" "T6" "T7"
"T8" "T9" "TK" "TK1" "TK2" "TK3" "TK4" "TK5" "TK6" "TK7"
"TK8" "TK9" "TP" "TP1" "TP2" "TP3" "TP4" "TP5" "TP6" "TP7"
"TP8" "TP9" "TPK" "TPK1" "TPK2" "TPK3" "TPK4" "TPK5" "TPK6"
"TPK7" "TPK8" "TPK9" "1V" "1V1" "1V2" "1V3" "1V4" "1V5"
"1V6" "1V7" "1V8" "1V9" "1VK" "1VK1" "1VK2" "1VK3" "1VK4"
"1VK5" "1VK6" "1VK7" "1VK8" "1VK9" "1VP" "1VP1" "1VP2"
"1VP3" "1VP4" "1VP5" "1VP6" "1VP7" "1VP8" "1VP9" "1VPK"
"1VPK1" "1VPK2" "1VPK3" "1VPK4" "1VPK5" "1VPK6" "1VPK7"
"1VPK8" "1VPK9" "1VT" "1VT1" "1VT2" "1VT3" "1VT4" "1VT5"
"1VT6" "1VT7" "1VT8" "1VT9" "1VTK" "1VTK1" "1VTK2" "1VTK3"
"1VTK4" "1VTK5" "1VTK6" "1VTK7" "1VTK8" "1VTK9" "1VTP"
"1VTP1" "1VTP2" "1VTP3" "1VTP4" "1VTP5" "1VTP6" "1VTP7"
"1VTP8" "1VTP9" "1VTPK" "1VTPK1" "1VTPK2" "1VTPK3" "1VTPK4"
"1VTPK5" "1VTPK6" "1VTPK7" "1VTPK8" "1VTPK9" "2V" "2V1"
"2V2" "2V3" "2V4" "2V5" "2V6" "2V7" "2V8" "2V9" "2VK" "2VK1"
"2VK2" "2VK3" "2VK4" "2VK5" "2VK6" "2VK7" "2VK8" "2VK9"
"2VP" "2VP1" "2VP2" "2VP3" "2VP4" "2VP5" "2VP6" "2VP7"
"2VP8" "2VP9" "2VPK" "2VPK1" "2VPK2" "2VPK3" "2VPK4" "2VPK5"
"2VPK6" "2VPK7" "2VPK8" "2VPK9" "2VT" "2VT1" "2VT2" "2VT3"
"2VT4" "2VT5" "2VT6" "2VT7" "2VT8" "2VT9" "2VTK" "2VTK1"
"2VTK2" "2VTK3" "2VTK4" "2VTK5" "2VTK6" "2VTK7" "2VTK8"
"2VTK9" "2VTP" "2VTP1" "2VTP2" "2VTP3" "2VTP4" "2VTP5"
"2VTP6" "2VTP7" "2VTP8" "2VTP9" "2VTPK" "2VTPK1" "2VTPK2"
"2VTPK3" "2VTPK4" "2VTPK5" "2VTPK6" "2VTPK7" "2VTPK8"
"2VTPK9" "3V" "3V1" "3V2" "3V3" "3V4" "3V5" "3V6" "3V7"
"3V8" "3V9" "3VK" "3VK1" "3VK2" "3VK3" "3VK4" "3VK5" "3VK6"
"3VK7" "3VK8" "3VK9" "3VP" "3VP1" "3VP2" "3VP3" "3VP4"
"3VP5" "3VP6" "3VP7" "3VP8" "3VP9" "3VPK" "3VPK1" "3VPK2"
"3VPK3" "3VPK4" "3VPK5" "3VPK6" "3VPK7" "3VPK8" "3VPK9"
"3VT" "3VT1" "3VT2" "3VT3" "3VT4" "3VT5" "3VT6" "3VT7"
"3VT8" "3VT9" "3VTK" "3VTK1" "3VTK2" "3VTK3" "3VTK4" "3VTK5"
"3VTK6" "3VTK7" "3VTK8" "3VTK9" "3VTP" "3VTP1" "3VTP2"
"3VTP3" "3VTP4" "3VTP5" "3VTP6" "3VTP7" "3VTP8" "3VTP9"
"3VTPK" "3VTPK1" "3VTPK2" "3VTPK3" "3VTPK4" "3VTPK5"
"3VTPK6" "3VTPK7" "3VTPK8" "3VTPK9" "4V" "4V1" "4V2" "4V3"
"4V4" "4V5" "4V6" "4V7" "4V8" "4V9" "4VK" "4VK1" "4VK2"
"4VK3" "4VK4" "4VK5" "4VK6" "4VK7" "4VK8" "4VK9" "4VP"
"4VP1" "4VP2" "4VP3" "4VP4" "4VP5" "4VP6" "4VP7" "4VP8"
"4VP9" "4VPK" "4VPK1" "4VPK2" "4VPK3" "4VPK4" "4VPK5"
"4VPK6" "4VPK7" "4VPK8" "4VPK9" "4VT" "4VT1" "4VT2" "4VT3"
"4VT4" "4VT5" "4VT6" "4VT7" "4VT8" "4VT9" "4VTK" "4VTK1"
"4VTK2" "4VTK3" "4VTK4" "4VTK5" "4VTK6" "4VTK7" "4VTK8"
"4VTK9" "4VTP" "4VTP1" "4VTP2" "4VTP3" "4VTP4" "4VTP5"
"4VTP6" "4VTP7" "4VTP8" "4VTP9" "4VTPK" "4VTPK1" "4VTPK2"
"4VTPK3" "4VTPK4" "4VTPK5" "4VTPK6" "4VTPK7" "4VTPK8"
"4VTPK9" "5V" "5V1" "5V2" "5V3" "5V4" "5V5" "5V6" "5V7"
"5V8" "5V9" "5VK" "5VK1" "5VK2" "5VK3" "5VK4" "5VK5" "5VK6"
"5VK7" "5VK8" "5VK9" "5VP" "5VP1" "5VP2" "5VP3" "5VP4"
"5VP5" "5VP6" "5VP7" "5VP8" "5VP9" "5VPK" "5VPK1" "5VPK2"
"5VPK3" "5VPK4" "5VPK5" "5VPK6" "5VPK7" "5VPK8" "5VPK9"
"5VT" "5VT1" "5VT2" "5VT3" "5VT4" "5VT5" "5VT6" "5VT7"
"5VT8" "5VT9" "5VTK" "5VTK1" "5VTK2" "5VTK3" "5VTK4" "5VTK5"
"5VTK6" "5VTK7" "5VTK8" "5VTK9" "5VTP" "5VTP1" "5VTP2"
"5VTP3" "5VTP4" "5VTP5" "5VTP6" "5VTP7" "5VTP8" "5VTP9"
"5VTPK" "5VTPK1" "5VTPK2" "5VTPK3" "5VTPK4" "5VTPK5"
"5VTPK6" "5VTPK7" "5VTPK8" "5VTPK9" "6V" "6V1" "6V2" "6V3"
"6V4" "6V5" "6V6" "6V7" "6V8" "6V9" "6VK" "6VK1" "6VK2"
"6VK3" "6VK4" "6VK5" "6VK6" "6VK7" "6VK8" "6VK9" "6VP"
"6VP1" "6VP2" "6VP3" "6VP4" "6VP5" "6VP6" "6VP7" "6VP8"
"6VP9" "6VPK" "6VPK1" "6VPK2" "6VPK3" "6VPK4" "6VPK5"
"6VPK6" "6VPK7" "6VPK8" "6VPK9" "6VT" "6VT1" "6VT2" "6VT3"
"6VT4" "6VT5" "6VT6" "6VT7" "6VT8" "6VT9" "6VTK" "6VTK1"
"6VTK2" "6VTK3" "6VTK4" "6VTK5" "6VTK6" "6VTK7" "6VTK8"
"6VTK9" "6VTP" "6VTP1" "6VTP2" "6VTP3" "6VTP4" "6VTP5"
"6VTP6" "6VTP7" "6VTP8" "6VTP9" "6VTPK" "6VTPK1" "6VTPK2"
"6VTPK3" "6VTPK4" "6VTPK5" "6VTPK6" "6VTPK7" "6VTPK8"
"6VTPK9" "7V" "7V1" "7V2" "7V3" "7V4" "7V5" "7V6" "7V7"
"7V8" "7V9" "7VK" "7VK1" "7VK2" "7VK3" "7VK4" "7VK5" "7VK6"
"7VK7" "7VK8" "7VK9" "7VP" "7VP1" "7VP2" "7VP3" "7VP4"
"7VP5" "7VP6" "7VP7" "7VP8" "7VP9" "7VPK" "7VPK1" "7VPK2"
"7VPK3" "7VPK4" "7VPK5" "7VPK6" "7VPK7" "7VPK8" "7VPK9"
"7VT" "7VT1" "7VT2" "7VT3" "7VT4" "7VT5" "7VT6" "7VT7"
"7VT8" "7VT9" "7VTK" "7VTK1" "7VTK2" "7VTK3" "7VTK4" "7VTK5"
"7VTK6" "7VTK7" "7VTK8" "7VTK9" "7VTP" "7VTP1" "7VTP2"
"7VTP3" "7VTP4" "7VTP5" "7VTP6" "7VTP7" "7VTP8" "7VTP9"
"7VTPK" "7VTPK1" "7VTPK2" "7VTPK3" "7VTPK4" "7VTPK5"
"7VTPK6" "7VTPK7" "7VTPK8" "7VTPK9" "8V" "8V1" "8V2" "8V3"
"8V4" "8V5" "8V6" "8V7" "8V8" "8V9" "8VK" "8VK1" "8VK2"
"8VK3" "8VK4" "8VK5" "8VK6" "8VK7" "8VK8" "8VK9" "8VP"
"8VP1" "8VP2" "8VP3" "8VP4" "8VP5" "8VP6" "8VP7" "8VP8"
"8VP9" "8VPK" "8VPK1" "8VPK2" "8VPK3" "8VPK4" "8VPK5"
"8VPK6" "8VPK7" "8VPK8" "8VPK9" "8VT" "8VT1" "8VT2" "8VT3"
"8VT4" "8VT5" "8VT6" "8VT7" "8VT8" "8VT9" "8VTK" "8VTK1"
"8VTK2" "8VTK3" "8VTK4" "8VTK5" "8VTK6" "8VTK7" "8VTK8"
"8VTK9" "8VTP" "8VTP1" "8VTP2" "8VTP3" "8VTP4" "8VTP5"
"8VTP6" "8VTP7" "8VTP8" "8VTP9" "8VTPK" "8VTPK1" "8VTPK2"
"8VTPK3" "8VTPK4" "8VTPK5" "8VTPK6" "8VTPK7" "8VTPK8"
"8VTPK9" "9V" "9V1" "9V2" "9V3" "9V4" "9V5" "9V6" "9V7"
"9V8" "9V9" "9VK" "9VK1" "9VK2" "9VK3" "9VK4" "9VK5" "9VK6"
"9VK7" "9VK8" "9VK9" "9VP" "9VP1" "9VP2" "9VP3" "9VP4"
"9VP5" "9VP6" "9VP7" "9VP8" "9VP9" "9VPK" "9VPK1" "9VPK2"
"9VPK3" "9VPK4" "9VPK5" "9VPK6" "9VPK7" "9VPK8" "9VPK9"
"9VT" "9VT1" "9VT2" "9VT3" "9VT4" "9VT5" "9VT6" "9VT7"
"9VT8" "9VT9" "9VTK" "9VTK1" "9VTK2" "9VTK3" "9VTK4" "9VTK5"
"9VTK6" "9VTK7" "9VTK8" "9VTK9" "9VTP" "9VTP1" "9VTP2"
"9VTP3" "9VTP4" "9VTP5" "9VTP6" "9VTP7" "9VTP8" "9VTP9"
"9VTPK" "9VTPK1" "9VTPK2" "9VTPK3" "9VTPK4" "9VTPK5"
"9VTPK6" "9VTPK7" "9VTPK8" "9VTPK9")```

You can run the program at http://ideone.com/5lLuG2.

Pages: 1 2

### 4 Responses to “Mangarevan Counting”

1. Rutger said

In Python, abusing the eval() function.

```import string

K = 10
P = 20
T = 40
V = 80

def to_Mangarevan(x):
result = ""
n, r = divmod(x, V)
if n:
result += str(n)+"V"
if r > T:
result += "T"
r -= T
if r > P:
result += "P"
r -= P
if r > K:
result += "K"
r -= K
if r:
result += str(r)
return result

def from_Mangeravan(m):
m = m[::-1]
result = 0
for i,x in enumerate(m):
if i == 0 and x in string.digits:
result += eval(m[0])
if x in "KPT":
result += eval(x)
if i == len(m)-1 and x in string.digits:
result += eval(x)*V
return result

for x in [73, 219, 799, 164]:
print(x, to_Mangarevan(x))
assert x == from_Mangeravan(to_Mangarevan(x))

# output
# 73 TPK3
# 219 2VTK9
# 799 9VTPK9
# 164 2V4
```
2. Jussi Piitulainen said

(@Praxis, your parsing function does not look right. I see it missing newlines and cut short.)

```# In Julia 0.6.0 that was released just
# Only notation mava"3VTPK1" and binary addition
# Allow 0 digit and even mava"" as 0
# No overflow check
# Regex matching feels fragile, seems ok
# Suboptimal error message on no match
# Unsure of proper macro usage, returns actual value, seems ok
# Unsure of printing mechanism, show() using print() seems ok

module PracticalMangarevaCounting

export Mava, @mava_str
import Base: +, show

primitive type Mava 16 end

macro mava_str(digits)
mo = match(r"^((\d)V)?(T)?(P)?(K)?(\d)?\$", digits)
_, v, t, p, k, r = mo.captures
reinterpret(Mava, UInt16(+((v == nothing) ? 0 : parse(v) * 80,
(t == nothing) ? 0 : 40,
(p == nothing) ? 0 : 20,
(k == nothing) ? 0 : 10,
(r == nothing) ? 0 : parse(r))))
end

function show(io::IO, mava::Mava)
w = reinterpret(UInt16, mava)
v, r = divrem(w, 80)
t, r = divrem(r, 40)
p, r = divrem(r, 20)
k, r = divrem(r, 10)
print(io, "mava", '"',
v > 0 ? v : "",
v > 0 ? "V" : "",
t > 0 ? "T" : "",
p > 0 ? "P" : "",
k > 0 ? "K" : "",
r > 0 ? r : "",
'"')
end

function +(ma::Mava, va::Mava)
reinterpret(Mava, reinterpret(UInt16, ma) +
reinterpret(UInt16, va))
end

end
```
```julia> include("mangareva.jl")
PracticalMangarevaCounting

julia> using PracticalMangarevaCounting

julia> reinterpret(Mava, UInt16(73))
mava"TPK3"

julia> reinterpret(Mava, UInt16(219))
mava"2VTK9"

julia> reinterpret(Mava, UInt16(799))
mava"9VTPK9"

julia> mava"1VPK9" + mava"1"
mava"1VT"

julia> mava"3VPK3" + mava"2VTK9"
mava"6VK2"

```
3. programmingpraxis said

@Jussi: Fixed. Thanks. WordPress recently updated its editor, again, and every time they do something breaks.

4. Paul said

In Python with checks on input.

```prog = re.compile("^([1-9]V)?(T)?(P)?(K)?([1-9])?\$")
VALUE = {str(i)+"V": i*80 for i in range(1, 10)}
VALUE.update(dict(zip("TPK123456789", (40, 20, 10) + tuple(range(1, 10)))))

def man_to_dec(man):
m = prog.match(man)
if not m:
raise ValueError("not a valid Mangarevan format " + man)
return sum(VALUE[group] for group in filter(None, m.groups()))

def dec_to_man(n):
if not 1 <= n <= 799:
raise ValueError("Outside range [1, 799]")
res = []
d, m = divmod(n, 80)
if d:
res += [str(d), "V"]
for i, s in zip((40, 20, 10), "TPK"):
if m >= i:
m -= i
res.append(s)
if m:
res.append(str(m))
return "".join(res)
```