Expression calculator

Type a whole expression — functions, variables, parentheses. Hand-written parser, no eval.

WHAT IT WILL NOT DO

Double-precision arithmetic: integers above 2^53 lose digits and 23! up is approximate.
Numeric only — no equation solving, simplification or derivatives; variables are just slots.
No bitwise operators: use D06 for AND, OR, XOR and shifts, G02 for base conversion.