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‎Makefile

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# GNU Makefile for cpp-tutor/flex-bison-cpp
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# note: can run 'make calc1' or 'make calc2'
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FLEX = flex
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BISON = bison
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CPP = g++
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CPPFLAGS =
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CALC1 = calc1
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CALC2 = calc2
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AUTOGEN1 = Parser1.hpp Parser1.cpp Scanner1.hpp Scanner1.cpp
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AUTOGEN2 = Parser2.hpp Parser2.cpp Scanner2.cpp
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all: $(CALC1) $(CALC2)
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$(AUTOGEN1): lexer1.l grammar1.y
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$(FLEX) lexer1.l
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$(BISON) grammar1.y
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$(AUTOGEN2): lexer2.l grammar2.y
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$(FLEX) lexer2.l
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$(BISON) grammar2.y
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$(CALC1): $(AUTOGEN1)
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$(CPP) $(CPPFLAGS) -o $(CALC1) Parser1.cpp Scanner1.cpp
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$(CALC2): $(AUTOGEN2) Scanner2.hpp
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$(CPP) $(CPPFLAGS) -o $(CALC2) Parser2.cpp Scanner2.cpp
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clean:
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rm -f $(CALC1) $(AUTOGEN1) $(CALC2) $(AUTOGEN2)

‎Scanner2.hpp

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namespace calc { // note: depends upon FlexLexer.h and Parser2.hpp
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class Scanner : public yyFlexLexer {
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public:
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Scanner(std::istream& arg_yyin, std::ostream& arg_yyout)
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: yyFlexLexer(arg_yyin, arg_yyout) {}
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Scanner(std::istream* arg_yyin = nullptr, std::ostream* arg_yyout = nullptr)
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: yyFlexLexer(arg_yyin, arg_yyout) {}
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int lex(Parser::semantic_type *yylval); // note: this is the prototype we need
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};
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} // namespace calc

‎build_VS2019.bat

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@ECHO OFF
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@ECHO Generating: Scanner1.hpp Scanner1.cpp
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win_flex --wincompat lexer1.l
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@ECHO Generating: Parser1.hpp Parser1.cpp
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win_bison grammar1.y
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cl /EHsc /FeCalc1.exe Parser1.cpp Scanner1.cpp
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@ECHO Generating: Scanner2.cpp
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win_flex --wincompat lexer2.l
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@ECHO Generating: Parser2.hpp Parser2.cpp
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win_bison grammar2.y
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cl /EHsc /FeCalc2.exe /I. Parser2.cpp Scanner2.cpp

‎grammar1.y

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%{
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#include <iostream>
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#include <string>
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#include <cmath>
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#include "Scanner1.hpp"
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%}
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%require "3.7.4"
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%language "C++"
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%defines "Parser1.hpp"
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%output "Parser1.cpp"
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%define api.parser.class {Parser}
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%define api.namespace {calc}
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%define api.value.type variant
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%param {yyscan_t scanner}
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%code provides
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{
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#define YY_DECL \
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int yylex(calc::Parser::semantic_type *yylval, yyscan_t yyscanner)
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YY_DECL;
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}
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%token EOL LPAREN RPAREN
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%token <long long> INT
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%token <double> FLT
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%token <char> INTVAR FLTVAR
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%nterm <long long> iexp
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%nterm <double> fexp
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%nonassoc ASSIGN
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%left PLUS MINUS
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%left MULTIPLY DIVIDE MODULO
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%precedence UMINUS
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%precedence FACTORIAL
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%right EXPONENT
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%code
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{
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namespace calc {
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long long ivars['Z' - 'A' + 1];
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double fvars['z' - 'a' + 1];
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long long factorial(long long n) {
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if (n < 2) {
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return 1;
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}
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else {
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return n * factorial(n - 1);
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}
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}
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} // namespace calc
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} // %code
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%%
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lines : %empty
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| lines line
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;
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line : EOL { std::cerr << "Read an empty line.\n"; }
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| iexp EOL { std::cout << $1 << '\n'; }
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| fexp EOL { std::cout << $1 << '\n'; }
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| INTVAR ASSIGN iexp EOL { ivars[$1 - 'A'] = $3; }
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| FLTVAR ASSIGN fexp EOL { fvars[$1 - 'a'] = $3; }
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| error EOL { yyerrok; }
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;
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iexp : INT { $$ = $1; }
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| iexp PLUS iexp { $$ = $1 + $3; }
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| iexp MINUS iexp { $$ = $1 - $3; }
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| iexp MULTIPLY iexp { $$ = $1 * $3; }
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| iexp DIVIDE iexp { $$ = $1 / $3; }
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| iexp MODULO iexp { $$ = $1 % $3; }
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| MINUS iexp %prec UMINUS { $$ = -$2; }
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| iexp FACTORIAL { $$ = factorial($1); }
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| LPAREN iexp RPAREN { $$ = $2; }
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| INTVAR { $$ = ivars[$1 - 'A']; }
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;
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fexp : FLT { $$ = $1; }
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| fexp PLUS fexp { $$ = $1 + $3; }
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| fexp MINUS fexp { $$ = $1 - $3; }
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| fexp MULTIPLY fexp { $$ = $1 * $3; }
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| fexp DIVIDE fexp { $$ = $1 / $3; }
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| fexp EXPONENT fexp { $$ = pow($1, $3); }
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| MINUS fexp %prec UMINUS { $$ = -$2; }
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| LPAREN fexp RPAREN { $$ = $2; }
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| FLTVAR { $$ = fvars[$1 - 'a']; }
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;
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%%
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void calc::Parser::error(const std::string& msg) {
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std::cerr << msg << '\n';
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}
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int main() {
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yyscan_t scanner;
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yylex_init(&scanner);
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calc::Parser parser{ scanner };
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std::cout.precision(10);
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parser.parse();
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yylex_destroy(scanner);
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}

‎grammar2.y

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%{
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#include <iostream>
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#include <string>
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#include <cmath>
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#include <FlexLexer.h>
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%}
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%require "3.7.4"
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%language "C++"
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%defines "Parser2.hpp"
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%output "Parser2.cpp"
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%define api.parser.class {Parser}
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%define api.namespace {calc}
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%define api.value.type variant
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%parse-param {Scanner* scanner}
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%code requires
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{
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namespace calc {
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class Scanner;
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} // namespace calc
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} // %code requires
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%code
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{
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#include "Scanner2.hpp"
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#define yylex(x) scanner->lex(x)
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}
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%token EOL LPAREN RPAREN
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%token <long long> INT
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%token <double> FLT
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%token <char> INTVAR FLTVAR
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%nterm <long long> iexp
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%nterm <double> fexp
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%nonassoc ASSIGN
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%left PLUS MINUS
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%left MULTIPLY DIVIDE MODULO
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%precedence UMINUS
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%precedence FACTORIAL
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%right EXPONENT
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%code
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{
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namespace calc {
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long long ivars['Z' - 'A' + 1];
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double fvars['z' - 'a' + 1];
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long long factorial(long long n) {
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if (n < 2) {
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return 1;
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}
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return n * factorial(n - 1);
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}
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} // namespace calc
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} // %code
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%%
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lines : %empty
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| lines line
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;
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line : EOL { std::cerr << "Read an empty line.\n"; }
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| iexp EOL { std::cout << $1 << '\n'; }
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| fexp EOL { std::cout << $1 << '\n'; }
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| INTVAR ASSIGN iexp EOL { ivars[$1 - 'A'] = $3; }
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| FLTVAR ASSIGN fexp EOL { fvars[$1 - 'a'] = $3; }
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| error EOL { yyerrok; }
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;
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iexp : INT { $$ = $1; }
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| iexp PLUS iexp { $$ = $1 + $3; }
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| iexp MINUS iexp { $$ = $1 - $3; }
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| iexp MULTIPLY iexp { $$ = $1 * $3; }
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| iexp DIVIDE iexp { $$ = $1 / $3; }
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| iexp MODULO iexp { $$ = $1 % $3; }
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| MINUS iexp %prec UMINUS { $$ = -$2; }
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| iexp FACTORIAL { $$ = factorial($1); }
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| LPAREN iexp RPAREN { $$ = $2; }
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| INTVAR { $$ = ivars[$1 - 'A']; }
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;
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fexp : FLT { $$ = $1; }
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| fexp PLUS fexp { $$ = $1 + $3; }
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| fexp MINUS fexp { $$ = $1 - $3; }
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| fexp MULTIPLY fexp { $$ = $1 * $3; }
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| fexp DIVIDE fexp { $$ = $1 / $3; }
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| fexp EXPONENT fexp { $$ = pow($1, $3); }
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| MINUS fexp %prec UMINUS { $$ = -$2; }
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| LPAREN fexp RPAREN { $$ = $2; }
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| FLTVAR { $$ = fvars[$1 - 'a']; }
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;
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%%
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void calc::Parser::error(const std::string& msg) {
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std::cerr << msg << '\n';
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}

‎lexer1.l

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%{
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#include <cstdlib>
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#include "Parser1.hpp"
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using namespace calc;
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%}
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%option reentrant interactive noyywrap noyylineno nodefault outfile="Scanner1.cpp" header="Scanner1.hpp"
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dseq ([[:digit:]]+)
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dseq_opt ({dseq}?)
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frac (({dseq_opt}"."{dseq})|{dseq}".")
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exp ([eE][+-]?{dseq})
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exp_opt ({exp}?)
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integer ({dseq})
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float (({frac}{exp_opt})|({dseq}{exp}))
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intvar ([[:upper:]])
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fltvar ([[:lower:]])
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%%
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{integer} yylval->emplace<long long>(strtoll(yytext, nullptr, 10)); return Parser::token::INT;
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{float} yylval->emplace<double>(strtod(yytext, nullptr)); return Parser::token::FLT;
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{intvar} yylval->emplace<char>(yytext[0]); return Parser::token::INTVAR;
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{fltvar} yylval->emplace<char>(yytext[0]); return Parser::token::FLTVAR;
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"+" return Parser::token::PLUS;
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"-" return Parser::token::MINUS;
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"*" return Parser::token::MULTIPLY;
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"/" return Parser::token::DIVIDE;
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"%" return Parser::token::MODULO;
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"!" return Parser::token::FACTORIAL;
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"^" return Parser::token::EXPONENT;
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"(" return Parser::token::LPAREN;
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")" return Parser::token::RPAREN;
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"=" return Parser::token::ASSIGN;
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\n return Parser::token::EOL;
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<<EOF>> return Parser::token::YYEOF;
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. /* no action on unmatched input */
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%%
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// main() can't go here due to bug in flex 2.6.4

‎lexer2.l

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%{
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#include "Parser2.hpp"
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#include "Scanner2.hpp"
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#define YY_DECL int calc::Scanner::lex(calc::Parser::semantic_type *yylval)
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// workaround for bug in flex 2.6.4
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#define yypanic(X) (void)(X)
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%}
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%option c++ interactive noyywrap noyylineno nodefault outfile="Scanner2.cpp"
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dseq ([[:digit:]]+)
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dseq_opt ({dseq}?)
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frac (({dseq_opt}"."{dseq})|{dseq}".")
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exp ([eE][+-]?{dseq})
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exp_opt ({exp}?)
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integer ({dseq})
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float (({frac}{exp_opt})|({dseq}{exp}))
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intvar ([[:upper:]])
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fltvar ([[:lower:]])
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%%
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{integer} yylval->emplace<long long>(strtoll(YYText(), nullptr, 10)); return Parser::token::INT;
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{float} yylval->emplace<double>(strtod(YYText(), nullptr)); return Parser::token::FLT;
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{intvar} yylval->emplace<char>(YYText()[0]); return Parser::token::INTVAR;
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{fltvar} yylval->emplace<char>(YYText()[0]); return Parser::token::FLTVAR;
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"+" return Parser::token::PLUS;
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"-" return Parser::token::MINUS;
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"*" return Parser::token::MULTIPLY;
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"/" return Parser::token::DIVIDE;
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"%" return Parser::token::MODULO;
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"!" return Parser::token::FACTORIAL;
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"^" return Parser::token::EXPONENT;
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"(" return Parser::token::LPAREN;
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")" return Parser::token::RPAREN;
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"=" return Parser::token::ASSIGN;
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\n return Parser::token::EOL;
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<<EOF>> return Parser::token::YYEOF;
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. /* no action on unmatched input */
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%%
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int yyFlexLexer::yylex() {
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throw std::runtime_error("Invalid call to yyFlexLexer::yylex()");
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}
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int main() {
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calc::Scanner scanner{ std::cin, std::cerr };
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calc::Parser parser{ &scanner };
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std::cout.precision(10);
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parser.parse();
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}

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