Numbers

Three numeric types, each for a different job.

int overflow is an error

9223372036854775807 + 1     # runtime error, not a wraparound

Silent wraparound is a bug that surfaces far from its cause. Ecko refuses at the operation.

float equality is exact IEEE

0.1 + 0.2 == 0.3            # false
approx(0.1 + 0.2, 0.3)      # true
approx(a, b, 0.01)          # explicit epsilon

== on floats does what IEEE says, which is the honest answer. approx has a default epsilon of 1e-9.

decimal for money

price = 19.99m
qty = 3
subtotal = price * qty          # 59.97 exactly

tax_rate = decimal("0.0825")
total = subtotal + subtotal * tax_rate

print(0.1m + 0.2m)              # 0.3
print(0.1 + 0.2)                # 0.30000000000000004

The rules, chosen so money behaves:

• decimal mixes with int and the result is decimal. 5m == 5 is true.
• decimal with float is a hard error. A binary float has already lost

precision; letting it into an exact calculation would silently corrupt the result. Convert explicitly if you truly mean to.

• decimal(aFloat) is rejected. Pass a string - decimal("0.1") - to state

the exact value you want. decimal(x) does accept an int or a numeric string.

• +, -, * preserve scale, so cents are never dropped: 19.99m + 0.01m

is 20.00.

• / and % return the exact quotient normalized: decimal(10) / 4 is 2.5.
• Overflow and divide-by-zero raise, as with int.

Integer division truncates

7 / 2        # 3
7.0 / 2      # 3.5
float(7) / 2 # 3.5

A common surprise. Convert one operand when you want a fraction.

JSON

JSON has no exact-decimal type. json_encode emits a decimal as a plain number in its canonical text, and decoding gives back a float. A round trip through JSON is float-precision - if exactness must survive transport, send a string.

Maths

std.math has the constants and functions: pi, e, sqrt, sin, log, floor, clamp, gcd, isclose and the rest.