Comprehensions, Iteration and Loops

Basic forms

# all these return a new array, containing every value that was in mySource
array mySource
array myValue in mySource
array myValue in mySource with myValue
array myIndex, myValue in mySource with myValue

# with-clause specified as a block
array myIndex, myValue in mySource
  myValue

Types

Comprehensions start with a reserved word which indicates the type of the comprehension. The types are:

• True Comprehensions
  • array returns a new array
  • object returns a new object
• Comprehension-like loops
  • each returns the fromClause value or the value specified in the variableDefinition
  • find
    • with whenClause: returns the value of the first withClause and stops
    • without whenClause: returns the first, present value returned from withClause and stops
    • returns null if the iteration completes without finding a value.

Syntax

comprehension: type /from|in/? fromClause optionalClauses
comprehension: type variableDefinition /from|in/ fromClause optionalClauses

type:       /object|array|each|find/
fromClause: expression

optionalClauses: intoClause? byClause? whenClause? withClause?
intoClause: /into/     expression
byClause:   /by/       expression
whenClause: /when/     expression
withClause: /with|do/  expression
withClause: block

variableDefinition: functionParams

Variable Definition

Variable definition uses the same syntax as function parameters - without the parentheses. Order matters, as does the number of parameters:

• 0 variables - You don't have to specify any variables. Since the with-clause returns the value from each iteration by default, this can be useful. Usually you'll want to be able to access one or more of the loop variables.
• 1 variable: value
• 2 variables: key, value
• 3 variables: key, value, out

Where:

• key: is the index or property-name for the current value
• value: the current value
• out: the value the comprehension will return

Each iteration of the loop sets 'key', 'value' and 'out'.

When

# create a new array
# from every value in mySource
# that is true for: myTest value
array value in mySource when myTest value