Next section: Syntax of Dylan Files
Special function call syntax
Infix OperatorsCertain predefined operators are called using standard algebraic syntax. Operators and their arguments must be separated by whitespace or parentheses. All binary operators are left-associative, except for the assignment operator :=, which is right-associative.
These are listed in descending order of precedence. Operators within a group share the same precedence.unary - negative unary ~ not (boolean) binary ^ exponentiation binary * multiplication binary / division binary + addition binary - subtraction binary = equality binary == identity binary ~= not equals binary < less than binary > greater than binary <= less than or equals binary >= greater than or equals binary & and binary | or binary := assignExcept for the last three, all of these infix operators are functions. These functions are first class, like all Dylan functions, but in order to use one where a variable name is expected (for example, as the variable name in a define method, or as a function argument) the operator must be prefixed with the infix operator escape character (\).
The order of evaluation for general infix expressions is as follows:
In an expression of the formarg1 op ... op argnarg1 ... argn are evaluated in that order. The evaluation time of module variables that op 's are defined to invoke (e.g. the plus function for +), is unspecified.
The last three infix operators listed here (&, |, and :=) are syntax forms. They have special evaluation rules which are described where these forms are defined.
Slot ReferenceDylan provides a shorthand syntax for slot reference. The syntax argument.function applies function to argument. This syntax is usually used for slot reference, to access the function slot of the object argument.
This can be cascaded and is left associative (i.e., moo.goo.gai.pan gets the pan slot of the gai slot of the goo slot of moo.).
Examples:? america.capital "Washington, D.C." ? me.mother.current-husband.favorite-child == me #t
Dylan's left-to-right evaluation rule applies here: argument is evaluated first, followed by function.
Array ReferenceDylan provides a shorthand syntax for array reference. The syntax foo[i] is equivalent to the function call element(foo, i). The syntax foo[i1, i2, ... in] where n != 1 is equivalent to the function call aref (foo, i1, i2, ... in).
? define constant vect = #[7, 8, 9] defined vect ? vect 7
In expressions of the form
sequence[arg1, ..., argn]
sequence is evaluated first, then arg1 ... argn in that order.
The evaluation time of the variable <element in Dylan module> or <aref in Dylan module>, which this expression is defined to invoke, is unspecified.