test.red

https://drivy.engineering/ruby-lambda-composition/

Red []

GREET: func[val][rejoin ["hello " val]]
UPPER: func[val][uppercase val]

print GREET "world"
print UPPER "world"

PRESENT: func[val][upper greet val]

print PRESENT "world"

PRESENT: func[val][greet upper val]

print PRESENT "world"

TAX:           func[val][val * 5% + val]
FEE:           func[val][val + 1]
PREMIUM:       func[val][val + 10]
DISCOUNT:      func[val][val * 90%]
ROUND-TO-CENT: func[val][round/to val 0.01]
PRESENT:       func[val][pad/left val 7]

REGULAR-SET:    [FEE TAX      ROUND-TO-CENT PRESENT]
PREMIUM-SET:    [FEE PREMIUM  TAX           ROUND-TO-CENT PRESENT]
DISCOUNTED-SET: [FEE DISCOUNT TAX           ROUND-TO-CENT PRESENT]

apply-rules: func[b v][
  do append reverse copy b v
]

amount: 100

print["regular....:" apply-rules REGULAR-SET    amount]  ; 106.05
print["premium....:" apply-rules PREMIUM-SET    amount]  ; 116.55
print["discounted.:" apply-rules DISCOUNTED-SET amount]  ;  95.45