2016-12-16 research

Strict Shell - Current Overview

So the semester had ended, and many changes have been made to Strict Shell. In fact, now it even has a name! (Though the name may change, because how do you even say stsh?)
Well, here you will find all the new information on Strict Shell.

Grammar

program : stmt_list
        ;

decl_list : real_decl_list
          | /* nothing */
          ;

real_decl_list : decl COMMA decl_list
               | decl
               ;

decl : type id
     | type id ASSIGN expr
     | type id L_PAREN decl_list R_PAREN stmt_list END
     | ARRAY id ASSIGN L_BRACKET expr_list R_BRACKET
     ;

id : IDENTIFIER
   ;

stmt_list : stmt stmt_list
          |
          ;

stmt : decl SEMICOLON
     | FOR L_PAREN expr_or_nothing SEMICOLON expr_or_nothing SEMICOLON expr_or_nothing R_PAREN stmt_list END SEMICOLON
     | RETURN expr SEMICOLON
     | IF L_PAREN expr R_PAREN stmt_list END SEMICOLON
     | IF L_PAREN expr R_PAREN stmt_list ELSE stmt_list END SEMICOLON
     | expr SEMICOLON
     | PRINT expr_list SEMICOLON
     | WHILE L_PAREN expr R_PAREN stmt_list END SEMICOLON
     | BREAK SEMICOLON
     ;

expr_list : real_expr_list
          | /*nothing */
          ;

real_expr_list : expr COMMA real_expr_list
               | expr

expr_or_nothing : expr
                | /* nothing */
                ;

expr : or_expr ASSIGN expr
     | or_expr
     ;

or_expr : or_expr OR and_expr
        | and_expr
        ;

and_expr : and_expr AND expr_compare
         | expr_compare
         ;

expr_compare : expr_compare GT add_expr
             | expr_compare GE add_expr
             | expr_compare LT add_expr
             | expr_compare LE add_expr
             | expr_compare EQ add_expr
             | expr_compare NE add_expr
             | add_expr
             ;

add_expr : add_expr ADD mul_expr
         | add_expr MINUS mul_expr
         | mul_expr
         ;

mul_expr : mul_expr MULTIPLY exp_expr
          | mul_expr MOD exp_expr
          | mul_expr DIVIDE exp_expr
          | exp_expr
          ;

exp_expr : exp_expr EXPON un_expr
         | un_expr
         ;

un_expr : MINUS un_expr
        | NOT un_expr
        | incr_expr
        ;

incr_expr : expr_group INCREMENT
          | expr_group DECREMENT
          | expr_group
          ;

expr_group : L_PAREN expr R_PAREN
           | id L_PAREN expr_list R_PAREN
           | command
           ;

command :  L_BRACE expr_list R_BRACE
           | atomic
            ;

atomic : TRUE
       | FALSE 
       | id 
       | STRING_LITERAL
       | CHAR_LITERAL
       | INTEGER_LITERAL 
       | FLOAT_LITERAL 
       | COMMAND
       ;

type : STRING 
     | BOOLEAN 
     | INTEGER 
     | VOID
     | FLOAT 
     ;

Examples

Variables:

string $url = "http://blahblah.com"
int $day = 35; 
bool $is_True = True;
float $salary = 5600.00;
string $find = { find, $dir, "-type f" };

Running Commands:

{ firefox, $url };
{ wget, $url };
{ pkill, "-9", $pid }; 
{ find, $dir, "-type f", "-printf \"%p %s\n\"", "2>/dev/null" };

Functions:

string $summary()
    return { df, "-Th", $dir};
END;

Conditionals:

if ( $var == True )
    int $month = 9;
    int $day = 11;
    float $money = 32.32;
END;

Loops:

for ( $i = 0; $i < 10; $i++)
    {echo, $i};
END;

Types

Strict Shell has strong typing and enforces type safety, so operations are only allowd on matching types. This may change, since I have found it handy to add characters with integers in some sneaky computations, but we will see.

Evaluation

Evaluation is the next step in this process. I started evaluating expressions, but quickly fell into the strong typing trap. I also started statement evaluation, but not much can be finished until we take a step back from the language and come back with fresh eyes.

More updates to come in the Spring of 2017.

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