The goal is to development an interpreter for a subset of the SCL language. The interpreter can implemented in any of the following programming languages: C/C++, Java, Python, or Ada.

Interpreter

This consists of developing an interpreter for a minimal form (subset) of the SCL language. The specification of the grammar is given below.

The interpreter will process an SCL program and build some intermediate data structures. These data structures will then be interpreted to execute the program. All tokens in this language are separated by white space. The parsing algorithm should detect any syntactical or semantic error. The first such error discovered should cause an appropriate error message to be printed, and then the interpreter should terminate. Run-time errors should also be detected with appropriate error messages being printed.

rammar for the (subset of SCL) language Syntax Rules, see scl_subset.yy

Lexical Rules

identifier letter char_list char_list letter_digit char_list | letter_digit

literal_integer digit literal_integer | digit assignment_operator = le_operator <= lt_operator <

ge_operator >=

gt_operator > eq_operator = = ne_operator ~= add_operator + sub_operator - mul_operator * div_operator /

///// scl_subset.yy

%{ /* SCL A Scientific Computing Language // for the low-level programming

// First implemented as a pre-processor that generates C programs // Feb. 2016 // // Subset of SCL specified for YACC (Bison), Jan 2017

start : symbols forward_refs specifications globals implement ; symbols : | symbols symbol_def ; symbol_def : SYMBOL IDENTIFIER HCON ; forward_refs : | FORWARD frefs ; frefs : REFERENCES forward_list | forward_list ; forward_list : forwards | forward_list forwards ; forwards : | check_ext func_main dec_parameters ; check_ext : | MEXTERN ; func_main : | FUNCTION IDENTIFIER oper_type | MAIN {dec_main();} ; oper_type : RETURN chk_ptr chk_array ret_type ; chk_ptr : | POINTER {pointer_flag = true;} ; chk_array : | ARRAY array_dim_list ; array_dim_list : LB array_index RB | array_dim_list LB array_index RB ; array_index : IDENTIFIER | ICON ;

ret_type : TYPE type_name | STRUCT IDENTIFIER | STRUCTYPE IDENTIFIER ; type_name : MVOID | INTEGER | SHORT | REAL | FLOAT | DOUBLE | TBOOL | CHAR | TSTRING OF LENGTH ICON | TBYTE ;

specifications : | SPECIFICATIONS spec_list ; spec_list : spec_def | spec_list spec_def ; spec_def : ENUM | STRUCT ; globals : | GLOBAL declarations ; declarations : | DECLARATIONS ; implement : IMPLEMENTATIONS funct_list ; funct_list : funct_def | funct_list funct_def ; funct_def : funct_body ; funct_body: FUNCTION main_head parameters f_body ; main_head : MAIN | IDENTIFIER ; parameters : | PARAMETERS param_list ; param_list : param_def | param_list COMMA param_def ; param_def : identifier chk_const chk_ptr chk_array OF TYPE type_name ; chk_const : | CONSTANT ; f_body : BEGIN ENDFUN ; statement_list : statement | statement_list statement ; statement : if_statement | assignment_statement | while_statement | print_statement | repeat_statement ; if_statement : IF boolean_expression THEN statement_list ELSE statement_list ENDIF ;

while_statement : WHILE boolean_expression DO statement_list ENDWHILE ;

assignment_statement : LET identifier assignment_operator arithmetic_expression ;

repeat_statement : REPEAT statement_list UNTIL boolean_expression ENDREPEAT ;

print_statement : DISPLAY arg_list ; arg_list : args | arg_list comma args ; args : identifier | constant | string ; boolean_expression : arithmetic_exp relative_op arithmetic_exp ;

relative_op : le_operator | lt_operator | ge_operator | gt_operator | eq_operator | ne_operator ;

arithmetic_exp : arithmetic_exp add_operator mulexp | arithmetic_exp sub_operator mulexp | mulexp ; mulexp : mulexp mul_operator primary | mulexp div_operator primary | primary ; primary : left_paren arithmetic_exp right_paren | minus primary | constant | identifier ;