PLC Laboratory 2 - Revision history

Beh01: /* Example */

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Example

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Input specification

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Lexical analyzer

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Lexical analyzer

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 <syntaxhighlight lang="haskell" >
      -2 + (245 div 3);  // note
-mod 3
+mod 3 * hello
 </syntaxhighlight >
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 ''Your output can be different, it depends on your definition of tokens.''
 <syntaxhighlight lang="haskell" >
 OP:+
 LPAR
 NUM:245
 DIV
 NUM:3
-PPAR
+RPAR
 SEMICOLON
 NUM:2
 MOD
 NUM:3
 </syntaxhighlight >

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 Symbols can be separated by a sequence of spaces, tabs, and line breaks.
-Notes are preceded by a sequence <code>//</code> and continue to the end of the line.
+There can be notes in the input. Notes are preceded by a sequence <code>//</code> and continue to the end of the line.
 == Output specification ==

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 == Lexical analyzer ==
-Write a program, that reads an input and converts it into a sequence of lexical symbols – ''tokens''. Each token composes from a type and possibly a value.
+Write a program, that reads an input and converts it into a sequence of lexical symbols – ''tokens''. Each token is a pair, it composes from a type and possibly a value.
 The tokens definition depends on you, and it is considered a part of the solution.

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 == Lexical analyzer ==
-Write a program, that reads an input and converts it into a sequence of lexical symbols – tokens. Each token composes from a type and possibly a value.
+Write a program, that reads an input and converts it into a sequence of lexical symbols – ''tokens''. Each token composes from a type and possibly a value.
 The tokens definition depends on you, and it is considered a part of the solution.

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 * Output
-'Your output can be different, it depends on your definition of tokens.'
+''Your output can be different, it depends on your definition of tokens.''
 <syntaxhighlight lang="haskell" >
 OP:+

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 The input may be containing the following symbols:
 * ''identifiers'' - consisting of a sequence of letters and numbers starting with a letter
-* numbers - formed by a sequence of decimal digits
+* ''numbers'' - formed by a sequence of decimal digits
-* operators - symbols '+', '-', '*' and '/',
+* ''operators'' - symbols <code>'+', '-', '*' and '/'</code>,
-* delimiters - symbols '(', ')' and ';',
+* ''delimiters'' - symbols <code>'(', ')' and ';'</code>,
-* keywords - <code>div</code> and <code>mod</code>.
+* ''keywords'' - <code>div</code> and <code>mod</code>.
 Symbols can be separated by a sequence of spaces, tabs, and line breaks.
 Notes are preceded by a sequence <code>//</code> and continue to the end of the line.
 == Output specification ==

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	+	== Interpreter of Arithmetic Expressions ==

	+	Implement an interpreter of arithmetic expressions. These expressions contain <code>+, -, *, /</code> operators (with common priorities and left associativity) and parentheses.
	+
	+	To simplify the task, consider we have only binary operators. There are no unary operators in our language. Moreover, we can use only positive integers in our expressions.
	+
	+	== Input specification ==
	+
	+	The first line of the input contains a number <code>N</code>. It defines the number of expressions your program should evaluate. These expressions are on next <code>N</code> lines. Each line contains exactly one expression.
	+
	+	== Output specification ==
	+
	+	For each expression write one line containing the result – the computed value of the expression. If there is any error in the input, write text <code>ERROR</code> instead.
	+
	+	== Example ==
	+	* Input
	+	<syntaxhighlight lang="haskell" >
	+	2
	+	2 * (3+5)
	+	15 - 2**7
	+	</syntaxhighlight >
	+
	+	* Output
	+	<syntaxhighlight lang="haskell" >
	+	16
	+	ERROR
	+	</syntaxhighlight >