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AIL also included the {{code|FORWARD}} qualifier, used to insert [[forward declaration]]s, typically when two procedures call each other.{{sfn|Smith|1976|p=21}} {{code|RETURN}} worked as in C, exiting the procedure and returning to the caller, as well as optionally returning a value if the procedure uses one.{{sfn|Smith|1976|p=23}} Parameters passed to the procedures could be by {{code|VALUE}} or {{code|REFERENCE}}, the later allowing values to be passed back.{{sfn|Smith|1976|p=24}}
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The basic variable types in SAIL are [[Integer (computer science)|integers]], [[Floating-point arithmetic|reals]] (floating point), [[Boolean data type|booleans]], and [[String (computer science)|strings]].{{sfn|Smith|1976|p=2}} Type conversions were automatic, so {{code|INTEGER i;i←SQRT(5);}} would convert the value 5 to a double as that is what SQRT requires.{{sfn|Smith|1976|p=13}} Any of these types can be turned into an array by adding the {{code|ARRAY}} qualifier and placing the array bounds in brackets, for instance, {{code|REAL ARRAY weeks[1:52]);}}. SAIL supported 1-d and 2-d arrays.{{sfn|Smith|1976|p=4}}
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Strings were manipulated using [[array slicing]], with {{code|aStr[i TO j]}} returning the substring with characters from i to j, or {{code|aStr[i FOR j]}} which returned the substring starting at i and running for j characters.{{sfn|Smith|1976|p=12}} The {{code|INF}}(inity) keyword represented the end of the string, so one could {{code|aStr[i TO INF]}} to return everything from i on.{{sfn|Smith|1976|p=13}} String functions and operators included {{code|EQU}} for testing if two strings were equal,{{sfn|Smith|1976|p=11}}, the ampersand for concatenation, {{code|LENGTH}} and {{code|LOP}} which removes the first character from the string.{{sfn|Smith|1976|p=12}}
===Records and pointers===
The concept of [[Record (computer science)|records]] as a data type had only recently been introduced when SAIL was being written. This feature thus shows the signs of being "bolted on" to the language syntax. For instance a record structure was defined using the {{code|RECORD!CLASS}} statement: {{code|RECORD!CLASS person (STRING name, address; INTEGER accountnum; REAL balance)}}. This statement worked in a fashion similar to the {{code|RECORD}} statement in Pascal, defining the template for the record. To create a record, one used the {{code|NEW!RECORD}} statement, which returned a {{code|RECORD!POINTER}}. Pointers were typed, and could be typed to more than one type, for insntace, {{code|RECORD POINTER (person,university) rp;}} defines rp, a pointer to either a person or university record.{{sfn|Smith|1976|p=40}} Pointers could also be declared to point to {{code|ANY!CLASS}}.{{sfn|Smith|1976|p=41}} Accessing the data in a record was similarly idiosyncratic; to print the name file of a person, for instance, the syntax was {{code|PRINT(person:name[rp]);}}.{{sfn|Smith|1976|p=41}}
===Compiler directives===
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