Sloth Compiler in C#

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This is a reimagination of the "Good for Nothing" Compiler presented by Joel Pobar and Joe Duffy at PDC from 2005 using ideas from the Roslyn C#/VB compilers. For details on the original compiler see here

The key ideas here are to

• explore the compiler as a service approach that the Roslyn C#/VB compilers use
• explore using functional programming idoms in compiler design
• generate real executable output files

The code compiles a simple c-like language called "Sloth" and has support for variables, simple inputs/outputs and a for-loop.

Sloth Language Specification

We use Extended BNF with '[' and ']' for zero and once, and '{' and '}' for any number of repition including zero.

Lexical Specifications

Keywords 'var', 'for', 'to', 'do', 'end', 'read_int', 'print'

Symbols '=', '+', '-', '*', and '/'

White characters Space, tabulations, new line and line feed are the only white space characters supported.

Strings

	<string> := '"' { ? any character except double quote ? } '"'

Identifiers Identifiers start with a letter, followed by any number of alphanumeric characters plus the underscore. Identifiers are case sensitive.

	<ident> := ('a' .. 'z' | 'A' .. 'Z') {('a' .. 'z' | 'A' .. 'Z' | '0' .. '9' | '_')}

Numbers There are only numbers in Sloth.

	<int> := ('0' .. '9') { ('0' .. '9') }

Invalid characters Any other character is invalid.

Syntactic Specifications

<prgm> := <stmt> { <stmt> }
<stmt> := 'var' <ident> '=' <expr> ;
	| <ident> '=' <expr> ;
	| 'for' <ident> '=' <expr> 'to' <expr> 'do' <stmt> 'end' ;
	| 'read_int' <ident> ;
	| 'print' <expr> ;

<expr> := <add_expr> ( ('+' | '-') <add_expr>)* 
<add_expr> := <primary_expr> ( ('*' | '/') <primary_expr)*
<primary_expr> := <string>
	| <int>
	| <ident>

Operator precedence

Precedence	Operator	Description	Associativity
1	* /	Multiplication and division	Left-to-right
2	+ -	Addition and subtraction	Left-to-right

Semantics

TBD

Sample Programs

A simple program could look like this:

var x = 2;
var y = 4;
var z = y / x;
print z;
print "that's it folks!";

A program with a loop could look like this:

var ntimes = 0;
print "How much do you love this company? (1-10) ";
read_int ntimes;
var x = 0;
for x = 0 to ntimes do
   print "Developers!";
end;
print "Who said sit down?!!!!!";