grammar.peg

// MUSHcode Grammar with Uniform AST Structure
// Lemuel Canady, Jr (lem@digibear.io)

start = expression*

expression = _ e:(function / percent_substitution / string_literal / word) _ {
    return e;
}

function = bracket_function / standard_function

bracket_function = "[" _ f:standard_function _ "]" {
    return f;
}

standard_function = call:word "(" _ args:arg_list? _ ")" {
    return {
        type: "function",
        operator: {
            type: "word",
            value: call
        },
        args: args || []
    };
}

arg_list = head:arg tail:(_ "," _ arg)* {
    return [head, ...tail.map(item => item[3])].filter(arg => arg !== undefined);
}

arg = e:(function / percent_substitution / string_literal / word) { return e; } / "" { return null; }

word = w:[^%\[\](),\s"]+ { 
    return {
        type: "word",
        value: w.join("")
    };
}

string_literal = '"' content:([^"]* ('""' [^"]*)*) '"' {
    return {
        type: "string",
        value: content.join("").replace(/""/g, '"')
    };
}

percent_substitution = "%" substitution:[a-zA-Z0-9]+ {
    return {
        type: "substitution",
        value: substitution.join("")
    };
}

_ = [ \t\n\r]*