S-Expressions

The org.jfuncmachine.sexprlang.parser package provides a Parser class that reads a file or string containing one or more S-expressions and returns an SexprItem representing its contents.

By default, the parser only reads the first S-expression, so if you want to parse a whole file of S-expressions, you need to call the parser with the parseMultipleSexprs value set to true.

SexprItem and Subclasses

The SexprItem class is the base class for the possibly values in an S-expression. Its subclasses are:

Symbols

One place where there is some variation in S-expressions is in what constitutes a symbol. You can provide the parser with a class that implements SymbolMatcher, which defines a method to determine whether a character can appear as the first character in a symbol (isSymbolFirstCharacter) and a method to determine if a character can appear anywhere after the first character in a symbol (isSymbolChar). JFuncMachine provides a default matcher named JavaSymbolMatcher that uses the same rules as Java for symbols, and also JavaExtSymbolMatcher which allows ‘.’ to appear in a symbol, so that a symbol could represent a fully-qualified Java class name.

Example

Here is a snippet of Java code that parses a simple program expressed in an S-expression using its own custom matcher. The null is the name of the file that was parsed. The parser will embed the filename and line number where an S-expression starts in each SexprItem, which can be useful when interacting with JFuncMachine since it also allows filename and line number to be associated with expressions:

SexprItem item = Parser.parseString("""
    (define fact (n acc)
      (if (< n 2) acc
        (fact (- n 1) (* acc n))))

    (print "10! is %d" (fact 10 1))
                """, null, true, new IntlangSymbolMatcher());