[Contents]

2. Interpreter Architecture

2.4. Syntax Analyzer

2.4.2. Expression

The formal description of an expression syntax is:

 tag ::= UNOP tag
         NUMBER
         STRING
         '(' expression ')'
         VARIABLE { '[' expression_list ']' }
         FUNC '(' expression_list ')'
         .

 expression_list ::= expression [ ',' expression_list ] .
 expression_i(1) ::= tag .
 expression_i(i) := expression_i(i-1) [ OP(i) expression_i(i) ] .
 expression ::= expression_i(MAX_PREC) .

where

• OP(i) is a binary operator having precdence I
• UNOP is an unary operator
• NUMBER is a number (float or integer)
• STRING is a string
• VARIABLE is a symbol that is to a local or global variable
• FUNC is a function name, which is either a built-in function or a user defined function
• MAX_PREC is the maximal precedence

The syntax analyzer is written to match an expression whenever an expression syntax definition element is to be matched according to these rules. The list of built-in function, unary operators and binary operators are defined in the module "global" variables, BuiltInFunctions, Unaries, and Binaries.