expression_lite.h File Reference

#include <stddef.h>

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Typedefs
typedef struct expression *	expression_t

Functions
expression_t	expression_new (void)
	New blank expression. More...
void	expression_free (expression_t exp)
	Free an expression. More...
value_t	expression_evaluate (expression_t exp)
void	expression_to_string (char *dst_str, expression_t src_exp)
	Expression to String. More...
expression_t	string_to_expression (size_t str_len, char const *str)
	Convert String to an Expression. More...

Detailed Description

Date

May 3, 2014

Author

Craig Hesling

Does not include any other project header file. This ensures that there are no circular dependencies.

Typedef Documentation

expression_t

typedef struct expression* expression_t

Function Documentation

expression_evaluate()

value_t expression_evaluate

(

expression_t

exp

)

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expression_free()

void expression_free

(

expression_t

exp

)

Free an expression.

Parameters

exp	The expression to free

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expression_new()

expression_t expression_new

(

void

)

New blank expression.

This function creates the most basic empty expression.

Returns

A new empty expression

expression_to_string()

void expression_to_string	(	char *	dst_str,
		expression_t	src_exp
	)

Expression to String.

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string_to_expression()

expression_t string_to_expression	(	size_t	str_len,
		char const *	str
	)

Convert String to an Expression.

Parses a string into an expression.

Note

level was type int - changed to unsigned to temporarily quiet compiler

Bug:

Cannot parse negative numbers

Warning

Symbols must start with ALPHA chars to be properly identified.

Algorithm

Parsing Overview

• Step 1: Recording details about the string while scanning from left to right.
• Step 2: There are two real cases. The string is a single number (with no operations) or it is two sub-expressions joined by an operation.
  Cases:
  • If it is a simple number, we know how to parse it and create a value expression.
  • If it is not just a number, we want split the string about the operation at the lowest level. (in practice, we end up finding the one that is farthest left of the lowest level) We then construct a tree expression with the chosen operation and the sub-expression results from running the function recursively on each of the sub-strings.

Parameters

str_len	Length of given string
str	String to parse

Returns

The expression_t representation of the inputed string

Test:

Test for negative values

Todo:

Allow symbols to be detected when they start with numeric digits also. string_to_sym is already compatible.

< Store original index

< Used to explore the presence of a symbol parameter

Todo:

Do series of additional syntax checks here.

Todo:

Syntax Check: Check that level==0

Todo:

Syntax Check: Check that oparen_count==cparen_count

Note

left_buf and right_buf were changed to use malloc to avoid errors with C90 compilers

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