Welcome to Chapter 5 of the "Implementing a language with LLVM" tutorial. Parts 1-4 described the implementation of the simple @@ -69,10 +69,10 @@ have an if/then/else expression plus a simple 'for' loop.

Extending Kaleidoscope to support if/then/else is quite straightforward. It @@ -112,15 +112,12 @@ Since Kaleidoscope allows side-effects, this behavior is important to nail down.

Now that we know what we "want", lets break this down into its constituent pieces.

- -

Lexer Extensions for -If/Then/Else

Lexer Extensions for If/Then/Else

The lexer extensions are straightforward. First we add new variants for the relevant tokens:

@@ -153,11 +150,10 @@ stuff:

AST Extensions for - If/Then/Else

AST Extensions for If/Then/Else

To represent the new expression we add a new AST variant for it:

@@ -175,11 +171,10 @@ type expr =

Parser Extensions for -If/Then/Else

Parser Extensions for If/Then/Else

Now that we have the relevant tokens coming from the lexer and we have the AST node to build, our parsing logic is relatively straightforward. First we @@ -214,10 +209,10 @@ let rec parse_primary = parser

LLVM IR for If/Then/Else

Now that we have it parsing and building the AST, the final piece is adding LLVM code generation support. This is the most interesting part of the @@ -331,11 +326,10 @@ directly.

Code Generation for -If/Then/Else

Code Generation for If/Then/Else

In order to generate code for this, we implement the Codegen method for IfExprAST:

@@ -492,11 +486,13 @@ another useful expression that is familiar from non-functional languages...

+ -

'for' Loop Expression

Now that we know how to add basic control flow constructs to the language, we have the tools to add more powerful things. Lets add something more @@ -525,14 +521,11 @@ variables, it will get more useful.

As before, lets talk about the changes that we need to Kaleidoscope to support this.

- -

Lexer Extensions for -the 'for' Loop

Lexer Extensions for the 'for' Loop

The lexer extensions are the same sort of thing as for if/then/else:

@@ -559,11 +552,10 @@ the 'for' Loop

AST Extensions for -the 'for' Loop

AST Extensions for the 'for' Loop

The AST variant is just as simple. It basically boils down to capturing the variable name and the constituent expressions in the node.

@@ -580,11 +572,10 @@ type expr =

Parser Extensions for -the 'for' Loop

+ -

Full Code Listing

Here is the complete code listing for our running example, enhanced with the @@ -1562,8 +1553,8 @@ operators Chris Lattner
Erick Tryzelaar
- The LLVM Compiler Infrastructure
- Last modified: $Date: 2010-05-28 19:07:41 +0200 (Fri, 28 May 2010) $ + The LLVM Compiler Infrastructure
+ Last modified: $Date: 2011-04-23 02:30:22 +0200 (Sat, 23 Apr 2011) $ -- cgit v1.1

Kaleidoscope: Extending the Language: Control Flow

Chapter 5 Introduction

If/Then/Else