For loops in ocaml

Question

I want to do something like the following.

let switchgraph cases =
  let g = Graph.makeGraph() in
  let g = (Graph.addNode g 1) in
  for i = 2 to cases do 
    let g = (Graph.addNode g i) in
  done
  g

But apparently, this is not possible. How else can I achieve this?

Answer 1

There are two things you need to fix:

• you need to use references (see ref, := and !) for this, since let bindings are immutable
• to sequence two expressions, you need to use ;

Something like this should work:

let switchgraph cases =
    let g = ref (Graph.makeGraph()) in
    g := Graph.addNode (!g) 1;
    for i = 2 to cases do
        g := Graph.addNode (!g) i
    done;
    !g

Note that g is the reference, and !g the value.