platypus/PLATYPUS Grammar Specification.md

PLATYPUS Language Specification

2. Lexical Specification (INCOMPLETE)

NOTE: This is incredibly incomplete and broken, I am simply writing this down and will fix it as I read along the informal language specification provided to me

2.1 Input Elements and Tokens

    <input character> ->
        ASCII characters but not SEOF

    <input> ->
        <input elements> SEOF

    <input elements> ->
        <input element> | <input elements> <input element>

    <token> ->
        <variable identifier> | <keyword> | <floating-point literal>
        | <integer literal> | <string literal> | <separator> | <operator>

2.2 White Space

    <white space> ->
        ASCII SP character (space)
        | ASCII HT character (horizontal tab)
        | ASCII VT character (vertical tab)
        | ASCII FF character (form feed)
        | <line terminator>
    
    <line terminator> ->
        CR | LF | CR LF

2.3 Comments

    <comment> ->
        !< <opt_characters in line> <line terminator>

    <characters in line> ->
        <comment character> | <characters in line> <comment character>

    <comment character> ->
        <input character> but not <line terminator>

2.4 Variable Identifiers

    <variable identifier> ->
        <arithmetic variable identifier> | <string variable identifier>

    <arithmetic identifier> ->
        <letter> <opt_letters or digits>

    <letters or digits> ->
        <letter or digit> | <letters or digits> <letter or digit>
    
    <letter> -> one of
        [a-z][A-Z]

    <letter or digit> -> one of
        [a-z][A-Z][0-9]

    <string variable identifier> ->
        <arithmetic variable identifier># 

2.5 Keywords

    <keyword> ->
        PLATYPUS | IF | THEN | ELSE | USING | REPEAT | INPUT | OUTPUT

2.6 Integer Literals

    <integer literal> ->
        <decimal integer literal> | <octal integer literal>
    
    <decimal integer literal> ->
        0 | <non-zero digit> <opt_digits>

    <digits> ->
        <digit> | <digits> <digit>

    <digit> ->
        0 | <non-zero digit>
    
    <non-zero digit> -> one of
        [1-9]

    <octal integer literal> ->
        0 <octal digit> <octal digits>

    <octal digit> ->
        0 | 1 | 2 | 3 | 4 | 5 | 6 | 7
    
    <octal digits> ->
        <octal digit> | <octal digits> <octal digit>
    

2.7 Floating-point Literals

    <floating-point literal> ->
        <decimal integer literal> . <opt_digits>

2.8 String Literals

    <string literal> ->
        "<opt_string characters>"

    <string chacters> ->
        <input character> | <string characters> <input character>

2.9 Separators

    <separator> -> one of
        ( ) { } , ; " .

2.10 Operators

    <operator> ->
        <arithmetic operator> | <string concatenation operator>
        | <relational operator> | <logical operator>
        | <assignment operator>
    
    <arithmetic operator> -> one of
        + - * /
    
    <string concatenation operator> -> one of
        > < == <>

    <logical operator> ->
        .AND. | .OR.

    <assignment operator> ->
        =

3. The PLATYPUS Syntatic Specification

3.1 PLATYPUS Program

    <program> ->
        PLATYPUS {<opt_statements>} SEOF
    
    <statements> ->
        <statement> | <statements> <statement>

3.2 Statements

    <statement> ->
        <assignment statement>
        | <selection statement>
        | <iteration statement>
        | <input statement>
        | <output statement>

3.3 Assignment Statement

    <assignment statement> ->
        <assignment expression>

    <assignment expression> ->
        AVID = <arithmetic expression>
        | SVID = <string expression>

3.2.2 Selection Statement (if statement)

    <selection statement> ->
        IF (<conditional expression>) THEN <statements>
        ELSE {<opt_statements>};

3.2.3 Iteration Statement (the loop statement)

    <iteration statement> ->
        <TBC>

3.2.4 Input Statement

    <input statement> ->
        INPUT (<variable list>);
    
    <variable list> ->
        <variable identifier> | <variable list>,<variable identifier>

3.2.5 Output Statement

    <output statement> ->
        <TBC>

3.3 Expressions

3.3.1 Arithmetic Expressions

    <arithmetic expression> ->
        <unary arithmetic expression>
        | <additive arithmetic expression>

    <unary arithmetic expression> ->
        - <primary arithmetic expression>
        | + <primary arithmetic expression

    <additive arithmetic expression> ->
        <additive arithmetic expression> + <multiplicative arithmetic expression>
        | <additive arithmetic expression> - <multiplicative arithmetic expression>
        | <multiplicative arithmetic expression>
    
    <multiplicative arithmetic expression> ->
        <multiplicative arithmetic expression> * <primary arithmetic expression>
        | <multiplicative arithmetic expression> / <primary arithmetic expression>
        | <primary arithmetic expression>

    <primary arithmetic expression> ->
        <variable identifier>
        | <floating-point literal>
        | <integer literal>
        | (<arithmetic expression>)

3.3.2 String Expression

    <string expression> ->
        <primary string expression>
        | <string expression> << <primary string expression>

    <primary string expression> ->
        <string variable identifier>
        | <string literal>

3.3.3 Conditional Expression

    <conditional expression> ->
        <logical OR expression>

    <logical OR expression> ->
        <TBC>

    <logical AND expression> ->
        <TBC>

3.3.4 Relational Expression

    <relational expression> ->
        <primary a_relational expression> == <primary a_relational expression>
        | <primary a_relational expression> <= <primary a_relational expression>
        | <primary a_relational expression> > <primary a_relational expression>
        | <primary a_relational expression> < <primary a_relational expression>
        | <primary s_relational expression> == <primary s_relational expression>
        | <primary s_relational expression> <= <primary s_relational expression>
        | <primary s_relational expression> > <primary s_relational expression>
        | <primary s_relational expression> < <primary s_relational expression>
    
    <primary a_relational expression> ->
        <floating-point literal>
        | <integer literal>
        | <variable identifier>

    <primary s_relational expression> ->
        <TBC>