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Diffstat (limited to 'standard-ml.html.markdown')
| -rw-r--r-- | standard-ml.html.markdown | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/standard-ml.html.markdown b/standard-ml.html.markdown index cc5132f1..8fc849cb 100644 --- a/standard-ml.html.markdown +++ b/standard-ml.html.markdown @@ -383,6 +383,25 @@ val test_poem = readPoem "roses.txt" (* gives [ "Roses are red,", "Violets are blue.", "I have a gun.", "Get in the van." ] *) + +(* We can create references to data which can be updated *) +val counter = ref 0 (* Produce a reference with the ref function *) + +(* Assign to a reference with the assignment operator *) +fun set_five reference = reference := 5 + +(* Read a reference with the dereference operator *) +fun equals_five reference = !reference = 5 + +(* We can use while loops for when recursion is messy *) +fun decrement_to_zero r = if !r < 0 + then r := 0 + else while !r >= 0 do r := !r - 1 + +(* This returns the unit value (in practical terms, nothing, a 0-tuple) *) + +(* To allow returning a value, we can use the semicolon to sequence evaluations *) +fun decrement_ret x y = (x := !x - 1; y) ``` ## Further learning |