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| -rw-r--r-- | standard-ml.html.markdown | 24 |
1 files changed, 22 insertions, 2 deletions
diff --git a/standard-ml.html.markdown b/standard-ml.html.markdown index b545f3e1..07896beb 100644 --- a/standard-ml.html.markdown +++ b/standard-ml.html.markdown @@ -3,13 +3,14 @@ language: "Standard ML" contributors: - ["Simon Shine", "http://shine.eu.org/"] - ["David Pedersen", "http://lonelyproton.com/"] + - ["James Baker", "http://www.jbaker.io/"] --- Standard ML is a functional programming language with type inference and some side-effects. Some of the hard parts of learning Standard ML are: Recursion, pattern matching, type inference (guessing the right types but never allowing -implicit type conversion). If you have an imperative background, not being able -to update variables can feel severely inhibiting. +implicit type conversion). Standard ML is distinguished from Haskell by including +references, allowing variables to be updated. ```ocaml (* Comments in Standard ML begin with (* and end with *). Comments can be @@ -383,6 +384,25 @@ 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 |