# package printer

`import "go/printer"`

Package printer implements printing of AST nodes..

## func Fprint

    func Fprint(output io.Writer, fset *token.FileSet, node interface{}) error

Fprint "pretty-prints" an AST node to output. It calls Config.Fprint with default settings.

    // Parse source file and extract the AST without comments for
    // this function, with position information referring to the
    // file set fset.
    funcAST, fset := parseFunc("example_test.go", "ExampleFprint")

    // Print the function body into buffer buf.
    // The file set is provided to the printer so that it knows
    // about the original source formatting and can add additional
    // line breaks where they were present in the source.
    var buf bytes.Buffer
    printer.Fprint(&buf, fset, funcAST.Body)

    // Remove braces {} enclosing the function body, unindent,
    // and trim leading and trailing white space.
    s := buf.String()
    s = s[1 : len(s)-1]
    s = strings.TrimSpace(strings.Replace(s, "\n\t", "\n", -1))

    // Print the cleaned-up body text to stdout.
    fmt.Println(s)

Output:

    funcAST, fset := parseFunc("example_test.go", "ExampleFprint")

    var buf bytes.Buffer
    printer.Fprint(&buf, fset, funcAST.Body)

    s := buf.String()
    s = s[1 : len(s)-1]
    s = strings.TrimSpace(strings.Replace(s, "\n\t", "\n", -1))

    fmt.Println(s)

## type CommentedNode

    type CommentedNode struct {
        Node     interface{} // *ast.File, or ast.Expr, ast.Decl, ast.Spec, or ast.Stmt
        Comments []*ast.CommentGroup
    }

A CommentedNode bundles an AST node and corresponding comments. It may be provided as argument to any of the Fprint functions.

## type Config

    type Config struct {
        Mode     Mode // default: 0
        Tabwidth int  // default: 8
        Indent   int  // default: 0 (all code is indented at least by this much)
    }

A Config node controls the output of Fprint.

## func (*Config) Fprint

    func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node interface{}) error

Fprint "pretty-prints" an AST node to output for a given configuration cfg. Position information is interpreted relative to the file set fset. The node type must be *ast.File, *CommentedNode, []ast.Decl, []ast.Stmt, or assignment-compatible to ast.Expr, ast.Decl, ast.Spec, or ast.Stmt.

## type Mode

    type Mode uint

A Mode value is a set of flags (or 0). They control printing.

    const (
        RawFormat Mode = 1 << iota // do not use a tabwriter; if set, UseSpaces is ignored
        TabIndent                  // use tabs for indentation independent of UseSpaces
        UseSpaces                  // use spaces instead of tabs for alignment
        SourcePos                  // emit //line comments to preserve original source positions
    )