Basics

Values and types

Taipan’s basic types are int (64-bit), float, bool, str and None. Every value has a type, known when the program compiles.

let answer = 42
let ratio = 0.75
let ready = True
let name = "Taipan"
print(answer, ratio, ready, name)

42 0.75 True Taipan

let, var and const

• let declares a name that can’t be reassigned.
• var declares one that can.
• const declares a top-level constant, visible everywhere, whose value is computed from literals.

const LIMIT = 3

var total = 0
for i in range(LIMIT):
    total += i
let message = f"total is {total}"
print(message)

total is 3

A type annotation is optional on let and var, and needed when the initializer doesn’t say enough, as with an empty list:

var names: list[str] = []
names.append("ada")
let limit: float = 10
print(names, limit)

["ada"] 10.0

Each block has its own scope. A name is visible from its declaration to the end of its block, and a name in an inner block can’t shadow one from an outer block.

Numbers

int arithmetic is checked: overflow raises OverflowError rather than wrapping. / always gives a float, // and % floor as in Python, and ** is a power.

print(7 / 2, 7 // 2, -7 // 2, 7 % 3, 2 ** 10)
print(1_000_000 * 3, 0.1 + 0.2)
print(int(3.9), float(2), round(2.5), abs(-4))

3.5 3 -4 1 1024
3000000 0.30000000000000004
3 2.0 2 4

An int is accepted where a float is expected. No other conversion is implicit.

Strings

Strings are immutable Unicode text, in "…" or '…'. F-strings take expressions and Python’s format specs:

let lang = "taipan"
let version = 0.4
print(lang.upper(), len(lang), lang[0], lang[-2:])
print(f"{lang!r} {version:.2f} {42:>5} {1234567:,}")
print(f"{lang=}")
print(", ".join(["a", "b", "c"]), "a,b".split(","))

TAIPAN 6 t an
"taipan" 0.40    42 1,234,567
lang="taipan"
a, b, c ["a", "b"]

Inside containers, and with !r, strings are written with double quotes.

Conditions

if, elif, else and while work as in Python, and a condition must be a bool. and, or and not take bools too.

def describe(n: int) -> str:
    if n < 0:
        return "negative"
    elif n == 0:
        return "zero"
    elif n % 2 == 0 and n < 100:
        return "small and even"
    else:
        return "other"

for n in [-5, 0, 8, 7]:
    print(n, describe(n))

-5 negative
0 zero
8 small and even
7 other

Comparisons don’t chain: write 0 < x and x < 10 rather than 0 < x < 10.

Loops

for goes over anything iterable: lists, strings, dicts, ranges and generators. while repeats while its condition holds, and break and continue work as in Python.

for i in range(10, 0, -3):
    print(i, end=" ")
print()

var n = 27
var steps = 0
while n != 1:
    if n % 2 == 0:
        n = n // 2
    else:
        n = 3 * n + 1
    steps += 1
print(steps)

10 7 4 1
111

Printing and input

print takes Python’s sep, end, file and flush arguments; print(x, file=sys.stderr) writes to standard error, after import sys. input() reads a line from standard input.

print("a", "b", sep="-")
print("no newline", end="")
print()

a-b
no newline

There’s no conditional expression (a if c else b). Use an if statement, or a match expression:

let n = 7
let parity = match n % 2 == 0:
    True: "even"
    False: "odd"
print(parity)

odd

Next: Collections.