97 lines
3.0 KiB
Markdown
97 lines
3.0 KiB
Markdown
# Elna programming language
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Elna is a simple, imperative, low-level programming language.
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It is intendet to accompany other languages in the areas, where a high-level
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language doesn't fit well. It is also supposed to be an intermediate
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representation for a such high-level hypothetical programming language.
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## File extension
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.elna
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## Current implementation
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This repository contains a GCC frontend for Elna. After finishing the frontend
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I'm planning to rewrite the compiler in Elna itself with its own backend and
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a hand-written parser. So GCC gives a way to have a simple bootstrap compiler
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and a possbility to compile Elna programs for different platforms.
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## Grammar
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```ebnf
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digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9";
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letter = "A" | "B" | … | "Z" | "a" | "b" | … | "z";
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ident = letter { letter | digit | "_" };
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integer = digit { digit };
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float = integer "." integer;
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boolean = "true" | "false";
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literal = integer | float | boolean | "'" character "'" | """ { character } """;
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program = [ "type" type_definitions ";" ]
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[ constant_part ]
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{ procedure_definition }
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[ variable_part ]
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compound_statement ".";
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procedure_definition = "proc" ident formal_parameter_list ";" ( block | "extern" ) ";";
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block = [ constant_part ]
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[ variable_part ]
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statement;
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constant_part = "const" ident "=" integer { "," ident "=" integer } ";";
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variable_part = "var" variable_declarations ";";
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statement = compound_statement
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| ident ":=" expression
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| ident actual_parameter_list
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| "while" condition "do" statement
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| "if" expression "then" statement [ else statement ];
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statement_list = statement {";" statement };
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compound_statement = "begin" [ statement_list ] "end";
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condition = "odd" expression |
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expression ("="|"#"|"<"|"<="|">"|">=") expression;
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comparison_operator = "=", "/=", "<", ">", "<=", ">=";
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unary_prefix = "not", "@";
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expression = logical_operand { ("and" | "or") logical_operand };
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logical_operand = comparand { comparison_operator comparand };
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comparand = summand { ("+" | "-") summand };
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summand = factor { ("*" | "/") factor };
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factor = pointer { unary_prefix pointer };
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pointer = literal
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| designator_expression { $$ = $1; }
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| "(" expression ")";
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designator_expression = designator_expression "[" expression "]"
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| designator_expression "." ident
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| designator_expression "^"
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| ident;
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formal_parameter_list = "(" [ variable_declarations ] ")";
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actual_parameter_list = "(" [ expressions ] ")";
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expressions = expression { "," expression };
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variable_declarations = variable_declaration { ";" variable_declaration };
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variable_declaration = ident ":" type_expression;
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type_expression = "array" integer "of" type_expression
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| "^" type_expression
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| "record" field_list "end"
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| ident;
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field_list = field_declaration { ";" field_declaration };
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field_declaration = ident ":" type_expression;
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```
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