CODEWITHSUNDEEP
sml
Tom
Tom

Reputation: 673

SML - if's condition with some "or"

I want to make a if condition like this:

if

 ((head(c) = 1) or (head(c) = ~1) or (head(c) = ~5) or (head(c) = ~17) or (head(c) = 0))
count +1
else..

the function head return 'a;

It gives me the next error: operator is not a function [tycon dismatch] operator: bool in expression

What is the problem? thank you.

Upvotes: 3

Views: 13164

Answers (3)

A. Mikhaylov
A. Mikhaylov

Reputation: 258

It's called orelse, not just or and andalso instead of and. But orelse and andalso are not functions. Citation from Programming in Standard ML '97:

Note in particular that andalso and orelse are not infix functions because they are not strict in their second argument—that is, they do not always force the evaluation of their second argument—and such functions cannot be defined in a strict programming language such as Standard ML. Thus we cannot apply the op keyword to andalso or orelse.

Upvotes: 5

tbrk
tbrk

Reputation: 1299

For this example, you could also write:

let val h = head c in
if List.exists (fn x => x = h) [1, ~1, ~5, ~17, 0]
then count + 1
else ...
end

Upvotes: 1

Omri Barel
Omri Barel

Reputation: 9480

I think it's called orelse in SML.

Upvotes: 9

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