Sollya User's Manual

Name:

parse parses an expression contained in a string

Library name:

sollya_obj_t sollya_lib_parse(sollya_obj_t)

Usage:

parse(string) : string -> function | error

Parameters:

string represents a character sequence

Description:

parse(string) parses the character sequence string containing an expression built on constants and base functions.

If the character sequence does not contain a well-defined expression, a warning is displayed indicating a syntax error and parse returns a error of type error.
The character sequence to be parsed by parse may contain commands that return expressions, including parse itself. Those commands get executed after the string has been parsed. parse(string) will return the expression computed by the commands contained in the character sequence string.
parse expects an expression (or a command returning an expression) but cannot be used to evaluate a command producing a side effect without returning a result, nor to evaluate a sequence of instructions. However, such a behavior may be obtained by encapsulating the side effects into an anonymous procedure that parse can handle and by immediately applying it (see examples below).

Example 1:

> parse("exp(x)");
exp(x)

Example 2:

   > text = "remez(exp(x),5,[-1;1])";
   > print("The string", text, "gives", parse(text));
   The string remez(exp(x),5,[-1;1]) gives 8.7381909882756203676868315731687604903964388498642e-3 * x^5 + 4.3793696379596015478233171265365272893795005588381e-2 * x^4 + 0.16642465614952768185129433844012193925654065755905 * x^3 + 0.49919698262963614991826575452094101562044819693772 * x^2 + 1.00003834650599815466340068058231011540878088492516 * x + 1.00004475029559502606203712816558243384077522932213

Example 3:

   > verbosity = 1!;
   > parse("5 + * 3");
   Warning: syntax error. Will try to continue parsing (expecting ";"). May leak memory.
   Warning: the string "5 + * 3" could not be parsed by the miniparser.
   Warning: at least one of the given expressions or a subexpression is not correctly typed
   or its evaluation has failed because of some error on a side-effect.
   error

Example 4:

   > i = 17;
   > parse("i = 42");
   error
   > i;
   17
   > (parse("proc () { i = 42; }"))();
   > i;
   42

See also: execute, readfile, print, error, dieonerrormode, proc

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