Layout and calls

Most Koskari in a .ki file looks like Python: a header line ending in a colon, then an indented body. Inside (, [, or { the reader switches to s-expression rules, which is why a nested call is still (+ 1 2).

Two rules

What does a line mean?

A line with more than one element is a call whose first element is the callee. A line with one element is that element. So print "hi" is (print "hi"), and x alone is the value of x.

What does a colon mean?

A line ending in : opens a block, and the indented lines under it are arguments to that line. def double [x]: followed by a body is one form, (def double [x] BODY...).

Functions

Python

def double(x):
    return x * 2

Koskari

def double [x]:
  (* x 2)

Where is return?

The last form in the body is the result. return exists for leaving early; Functions and scope covers it.

Python

double = lambda x: x * 2

Koskari

def double [x] (* x 2)

Why no colon on that one?

The body fits on the header line, so there is nothing to continue. A colon is only for a body that follows on indented lines.

Conditionals

Python

def sign(n):
    if n < 0:
        return "negative"
    elif n == 0:
        return "zero"
    else:
        return "positive"

Koskari

def sign [n]:
  if (< n 0):
    "negative"
  elif (== n 0):
    "zero"
  else:
    "positive"

Why is the test in parentheses?

(< n 0) is a call to <, and a call inside a header needs its parentheses. Only the line itself gets the implicit call.

Python

if n > 0:
    print(n)

if not ready:
    print("wait")

Koskari

when (> n 0):
  print n

unless ready:
  print "wait"

Where parentheses stay

When do I still write them?

Around a nested expression, an inner call on the line, formals and bindings, and a collection literal. The four places, each with an example, are in Koskari and s-expressions.

Run it

Save as sign.ki:

def sign [n]:
  if (< n 0):
    "negative"
  elif (== n 0):
    "zero"
  else:
    "positive"

@entry-point
def main []:
  print (sign -3)
  print (sign 0)
  print (sign 9)

koskari sign.ki

negative
zero
positive

The rules, each beside the s-expression it reads to, are in Koskari and s-expressions.