Control structures

Control structures

MSE Script has two types of control structures.

Conditional statement (if then else)

To switch between two options use:

 if condition then a else b

If the condition evaluates to true, then the expression evaluates to a, otherwise it evaluates to b. The else part is optional.

For example:

 if 1 + 1 == 2 then "yes sir!" else "something is wrong"

Will evaluate to "yes sir!".

Note that if-then-else is an expression, it can be used almost everywhere:

 1 + (if card.color == "red" then 1 else 2)
 color := (if card.color == "red"   then "r") +
          (if card.color == "green" then "g")

Multiple conditions can be checked by using else if:

 if      card.color == "white"  then "W"
 else if card.color == "red"    then "R"
 else if card.color == "blue"   then "U"
 else                                "something else"

The then and else parts can also contain assignments and other control structures.

 if card.color == "red" then
     filter := filter + "r"

To use multiple statements in the then or else branches you must use parentheses:

 # WRONG
 if 1 + 1 == 2 then
     x := y
     y := z
 # RIGHT
 if 1 + 1 == 2 then (
     x := y
     y := z
 )

Loop statement (for each)

To iterate over all elements in a list the for each construct can be used

 for each variable in list do expression

If list is a list of items, for example set.cards, the expression is evaluated for each item in that list. The variable becomes set to that each item in succession. The results of the expression are combined using the + operator:

 for each x in ["a","b","c"] do x      ==  "abc"
 for each x in ["a","b","c"] do [x+x]  ==  ["aa","bb","cc"]

When iterating over a map the key is also available:

 for each key:variable in list do expression

For example:

 (for each k:v in [name:"Thing", rank:"High"] do
     "Its {k} is {v}. "
 )  ==  "Its name is Thing. Its rank is High. "

When iterating over a list, the key is the index in the list, starting with 0:

 (for each k:v in ["a","b","c"] do
     ["element {k} is {v}"]
 )  ==  ["element 0 is a","element 1 is b","element 2 is c"]

It is also possible to iterate over a range of values:

 for variable from begin to end do expression

The expression is evaluated for each number from begin to end (including begin, not including end). The variable becomes set to that each number in succession. Again, the results of the expression are combined using +.

Summary

Syntax Description
if a then b else c If a is true evaluates to b, otherwise evaluates to c.
for each x in list do something Does something for each element in a list, adding the results
for each k:v in list do something Does something for each element in a map using the key/index in the map.
for x from 1 to 100 do something Does something for all numbers from 1 to 100.