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Expr is a simple recursive descent expression evaluator. It was originally written in C by Guy Laden. It can be used on the command line:
java Expr "(x+1) * (y%4) + cond(x<>y, 10, 0)" x 2 y 10 prints 16.0 or within a program:
Available functions are: + - * / ^ ? % sqrt() sin() cos() tan() asin() acos() atan() exp() ln() cond(,,) min(,) max(,) cond works somewhat like an if/then/else, or rather like the "a ? b : c" construct in C or Java. The first argument should evaluate to true or false (the numerical comparison operators can be used); if it's true, cond evaluates to the second argument, otherwise to the third. ? returns a random number between 0 and 1. Variables can be uppercase or lowercase; they override functions of the same name. "PI" and "E" are predefined to be the corresponding mathematical constants. Changes:
The source code is available here
CodeSnippets |