sml-windchill

Zero-dependency Standard ML library for apparent temperature indices: NWS wind chill, NOAA heat index (Rothfusz polynomial), Canadian humidex, Steadman apparent temperature, Magnus dew point, and unit-conversion helpers.

API

signature WINDCHILL =
sig
  val windChillF    : {tF:real, windMph:real} -> real      (* NWS formula *)
  val windChillC    : {tC:real, windKmh:real} -> real
  val heatIndexF    : {tF:real, rh:real} -> real           (* rh 0..100 % *)
  val heatIndexC    : {tC:real, rh:real} -> real
  val humidexC      : {tC:real, dewC:real} -> real
  val apparentTempC : {tC:real, rh:real, windMs:real} -> real  (* rh 0..1 *)
  val dewPointC     : {tC:real, rh:real} -> real               (* rh 0..1 *)
  val cToF : real -> real    val fToC : real -> real
  val kmhToMph : real -> real    val mphToKmh : real -> real
end

Usage example

val wc = Windchill.windChillF {tF=0.0, windMph=15.0}   (* ~-19 F *)
val hi = Windchill.heatIndexF {tF=90.0, rh=70.0}       (* ~105 F *)
val hx = Windchill.humidexC   {tC=30.0, dewC=25.0}     (* ~42 *)
val dp = Windchill.dewPointC  {tC=20.0, rh=0.5}        (* ~9.3 C *)

Example

make example builds and runs examples/demo.sml, which computes wind chill, heat index, humidex, Steadman apparent temperature, dew point, and unit conversions across representative inputs (output is byte-identical under MLton and Poly/ML):

Wind chill (NWS formula, Fahrenheit/mph):
  0F,  15mph -> ~19.40 F
  32F, 10mph -> 23.73 F
  60F, 20mph -> 60.00 F (out of range: T > 50F, returns input)

Wind chill (Celsius/km-h):
  -10C, 30km/h -> ~19.49 C

Heat index (Rothfusz polynomial):
  90F, 70% rh -> 105.92 F
  32C, 60% rh -> 37.07 C

Humidex (Canada):
  30C air, 25C dew point -> 42.34

Steadman apparent temperature:
  25C, 60% rh, 5m/s wind -> 23.75 C

Magnus dew point:
  20C, 50% rh -> 9.26 C

Unit conversions:
  0C -> 32.00 F,  100C -> 212.00 F
  32F -> 0.00 C
  100km/h -> 62.14 mph,  60mph -> 96.56 km/h

Scope and limitations

• Wind chill: NWS 2001 formula; returns input temperature when T > 50 °F or wind < 3 mph.
• Heat index: Rothfusz polynomial; rh is a percentage (0..100); returns input temperature below 80 °F.
• Humidex: Canadian formula using Buck vapour-pressure approximation.
• apparentTempC / dewPointC: rh is a fraction (0..1).
• No solar radiation or clothing corrections.

Build and test

make all-tests   # MLton + Poly/ML
make test        # MLton only
make test-poly   # Poly/ML only