Macro syntax

Reserved keywords

The following words are reserved and cannot be used as identifiers:

and by case do else end export extern for function global if import in include inline loop nil not object of on or otherwise repeat return task tell then to until when while

Comments

To write comments, use the character #. Any text from this character to the end of the line is ignored. Each line to be commented must be preceded by the # character, i.e. C-like multi-line comments are not allowed.

# Now plot the field
plot (Z500) # using default contours

Variables and scope

Variables declared in the program scope are not visible to functions unless they are declared global. This is usually discouraged, but an example is here:

global my_var = 5

function modify_my_var()
    my_var = 6
end modify_my_var

print(my_var)    # 5
modify_my_var()
print(my_var)    # 6

If the word global had not been present, the last line would have printed 5, because the function would have simply set the value of a local variable and not touched the one declared outside.

Loops

# basic for loop
for i = 1 to 4 do
    print (i)
end for

# for loop with a list
for i = 1 to count(thisList) do
    print (i, " : ", thisList[i])
end for

# for loop using dates with a step
for day = 2003-01-24 to 2003-02-14 by 3 do
    print (day)
end for

# basic while loop
n = 1
while n <= 10 do
    print(n)
    n = n + 1
end while

# basic repeat loop
n = 1
repeat
    print(n)
    n = n + 1
until n > 10

# loop - can be used on lists, fieldsets and geopoints
loop element in thisList
    print(element)
end loop

Tests

# basic if test
if a = b then
    print("a and b are equal")
end if

# if test with an else condition
if a = b then
    print("a and b are equal")
else print("a and b are different")
end if

# if test with an else if and an else condition
if a > 0 then
    print("a is positive")
else if a < 0 then
    print("a is negative")
else print("a is null")
end if

# when statement. The code following the first true expression is
# executed.
when
    a > 0 :
        print("a is positive")
        end
    a < 0 :
        print("a is negative")
        end
    a = 0 :
        print("a is null")
        end
end when

# case statement
case type(x) of
    "number" :
        print("x is a number")
        end
    "date" :
        print("x is a date")
        end
    otherwise :
        stop("Unsupported type")
        end
end case

Functions

You can define your own functions in Macro. Functions can take any number of input arguments and can optionally enforce type-checking on them. A function does not need to have a return value. Only one value can be returned - to return multiple values, return a structure such as a list, vector or definition containing the values.

The following examples show how to write functions in Macro.

# function that takes no arguments
function always_return_5 ()
    return 5
end always_return_5

five = always_return_5()  # 5

# function that takes an argument and does no type-checking
function add_10_untyped (a)
    return a+10
end add_10_untyped

b = add_10_untyped(4) # 14

# function that takes two arguments
function add_two_untyped (a, b)
    return a+b
end add_two_untyped

b = add_two_untyped(9, 11) # 20

# function that takes an argument that must be a number
function add_10_to_number (a:number)
    return a+10
end add_10_to_number

b = add_10_to_number(6) # 16
b = add_10_to_number('Hello')  # Run-time error

# function that returns a list of four values
function return_4_values_as_list(a)
    return [a+4, a+3, a+2, a+1]
end return_4_values

b = return_4_values_as_list(10) # [14,13,12,11]

# return four values as named elements of a structure
function return_4_values_as_definition(a)
    return (w: a+1, x: a+2, y:a+3, z:a+20)
end return_4_values_as_definition

b = return_4_values_as_definition(10) # (w:11,x:12,y:13,z:30)

# function that takes any number of arguments
function print_all_params
    loop arg in arguments()
        print(arg)
    end loop
end print_all_params

print_all_params(5, 6, 7, 'Hello')

Macro tutorial

To learn more about the Macro syntax, please follow the Metview Tutorials.