Standard ML Examples

-> Functionality "Evaluate Standard ML expression"
-> is implemented by shell command
-> "cp %(test-body-file) /tmp/foo.sml && echo ';printVal it' >>/tmp/foo.sml && mosml -quietdec /tmp/foo.sml"

-> Tests for functionality "Evaluate Standard ML expression"

Some basic expressions.

1
===> 1

~100 * ~100 * ~100
===> ~1000000

A conditional.

if true then 5 else 6
===> 5

The basic usage of let to create name bindings.

let val a = 2 in a end
===> 2

let fun r(x) = 77 in r(1) end
===> 77

let fun r(x) = x in r(66) end
===> 66

You can also use val and fn to define function values in a let.

let val r = fn(x) => x in r(66) end
===> 66

ML's let is like Scheme's let*: later bindings can refer to earlier ones.

let
  fun r(x) = x * 2
  fun p(x) = r(x) * 2
in
  p(10)
end
===> 40

However in a let, earlier bindings cannot refer to later ones.

Skipping because I don't know why mosml doesn't report this error under falderal. It does when you run it from the command line.

main() = let fun oddp(x) = if x = 0 then false else evenp(x - 1) fun evenp(x) = if x = 0 then true else oddp(x - 1) in evenp(6) end ???> Unbound value identifier: evenp

You need to use rec in order to let earlier bindings refer to later ones, and you need to use and between all the mutually recursive functions.

let
  val rec oddp = fn(x)  => if x = 0 then false else evenp(x - 1)
  and rec evenp = fn(x) => if x = 0 then true else oddp(x - 1)
in
  evenp(6)
end
===> true

let
  val rec oddp = fn(x)  => if x = 0 then false else evenp(x - 1)
  and rec evenp = fn(x) => if x = 0 then true else oddp(x - 1)
in
  evenp(7)
end
===> false