ref: 41e27b2d10c6a60c49931332e8677438736a1e36
dir: /man/6/ubfa/
.TH UBFA 6 .SH NAME ubfa \- universal binary format for data transport .SH DESCRIPTION .I UBF(A) is the data transport encoding for Armstrong's Universal Binary Format. It provides four primitive types: atoms (symbolic constants), integers, strings, and binary data. There are two compound types: fixed-length tuples and variable-length lists. .IR Ubfa (2) provides basic support in Limbo for reading and writing streams of UBF(A)-encoded data. .PP The .I input syntax is defined by the following rules: .IP .EX .ft R .ta \w'\f2simple-xxx\f1'u +\w'\ ::=\ 'u \f2input\fP ::= \f2item\fP* '$' \f2item\fP ::= \f2integer\fP | \f2atom\fP | \f2string\fP | \f2binary\fP | \f2tuple\fP | \f2list\fP | \f2store\fP | \f2push\fP | \f2comment\fP | \f2tag\fP \f2integer\fP ::= \f5'-'\fP?\f5[0-9]\fP+ \f2atom\fP ::= "'" (\f5[^\e']\fP | '\e\e' | "\e'")* "'" \f2string\fP ::= '"' (\f5[^\e"]\fP | '\e\e' | '\e"')* '"' \f2binary\fP ::= '~' \f2byte\fP* '~' # preceded by \f2integer\fP byte count \f2tuple\fP ::= '{' \f2item\fP* '}' \f2list\fP ::= '#' (\f2item\fP '&')* \f2store\fP ::= '>' \f2reg\fP \f2push\fP ::= \f2reg\fP \f2reg\fP ::= \f5[^-%"~'`{}#& \en\er\et,0-9]\fP \f2comment\fP ::= '%' (\f5[^\e%]\fP | '\e\e' | '\e%')* '%' \f2tag\fP ::= '`' (\f5[^\e`]\fP | '\e\e' | '\e`')* '`' .EE .PD .DT .PP White space is any sequence of blank, tab, newline or carriage-return characters, and can appear before or after any instance of .I item in the grammar. .PP The .I input data is interpreted by a simple virtual machine. The machine contains a stack of values of primitive and compound types, and a set of registers also containing values of those types. White space and comments are ignored. Primitive .IR integer , .I atom and .IR string values are pushed onto the stack as they are recognised. Certain input bytes outside any value act as operators: .TP .B { Note the current stack depth. .TP .B } Pop stack values to restore the most recently noted stack depth. Push a single value representing a tuple of those items; the left-most value in the tuple is the last one popped (the first in the original input stream). .TP .B ~ Pop an integer value .I n from the stack. Read .I n bytes from the input stream and push a value onto the stack that represents them. The next byte must be the character .BR ~ , which is discarded. .TP .B # Push a value representing an empty list onto the stack. .TP .B & Pop a value .IR v . Pop another value .IR l , which must represent a list. Push a value that represents the list .IB v :: l . (Note that the items in a .I list therefore appear in reverse order in the input stream.) .TP .BI > reg Pop the top value from the stack and store it in a register labelled by the byte .IR reg . .TP .I reg Push the value of register .I reg (which must be non-null) onto the stack. .TP .I tag Associate the tag string with the value on top of the stack. The .IR ubfa (2) implementation does so by replacing it by a special .B Tag tuple. .TP .B $ End-of-input: there must be exactly one value on the stack, which is the result. .PP Applications using UBF(A) typically take turns to exchange .I input values on a communication channel. .SH SEE ALSO .IR ubfa (2), .IR json (6), .IR sexprs (6) .br J L Armstrong, ``Getting Erlang to talk to the outside world'', .I "ACM SIGPLAN Erlang workshop 2002" , Pittsburg, PA USA .br UBF web page, .B "http://www.sics.se/~joe/ubf/"