1erl_pp(3)                  Erlang Module Definition                  erl_pp(3)
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3
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NAME

6       erl_pp - The Erlang pretty printer.
7

DESCRIPTION

9       The functions in this module are used to generate aesthetically attrac‐
10       tive representations of abstract forms, which are suitable  for  print‐
11       ing.  All functions return (possibly deep) lists of characters and gen‐
12       erate an error if the form is wrong.
13
14       All functions can have an optional argument,  which  specifies  a  hook
15       that is called if an attempt is made to print an unknown form.
16

DATA TYPES

18       hook_function() =
19           none |
20           fun((Expr :: erl_parse:abstract_expr(),
21                CurrentIndentation :: integer(),
22                CurrentPrecedence :: integer() >= 0,
23                Options :: options()) ->
24                   io_lib:chars())
25
26              Optional argument HookFunction, shown in the functions described
27              in this module, defines  a  function  that  is  called  when  an
28              unknown  form occurs where there is to be a valid expression. If
29              HookFunction is equal to none, there is no hook function.
30
31              The called hook function is to return a (possibly deep) list  of
32              characters. Function expr/4 is useful in a hook.
33
34              If  CurrentIndentation is negative, there are no line breaks and
35              only a space is used as a separator.
36
37       option() =
38           {hook, hook_function()} |
39           {encoding, latin1 | unicode | utf8} |
40           {quote_singleton_atom_types, boolean()}
41
42              The option quote_singleton_atom_types is used to add  quotes  to
43              all singleton atom types.
44
45       options() = hook_function() | [option()]
46

EXPORTS

48       attribute(Attribute) -> io_lib:chars()
49
50       attribute(Attribute, Options) -> io_lib:chars()
51
52              Types:
53
54                 Attribute = erl_parse:abstract_form()
55                 Options = options()
56
57              Same as form/1,2, but only for attribute Attribute.
58
59       expr(Expression) -> io_lib:chars()
60
61       expr(Expression, Options) -> io_lib:chars()
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63       expr(Expression, Indent, Options) -> io_lib:chars()
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65       expr(Expression, Indent, Precedence, Options) -> io_lib:chars()
66
67              Types:
68
69                 Expression = erl_parse:abstract_expr()
70                 Indent = integer()
71                 Precedence = integer() >= 0
72                 Options = options()
73
74              Prints  one expression. It is useful for implementing hooks (see
75              section Known Limitations).
76
77       exprs(Expressions) -> io_lib:chars()
78
79       exprs(Expressions, Options) -> io_lib:chars()
80
81       exprs(Expressions, Indent, Options) -> io_lib:chars()
82
83              Types:
84
85                 Expressions = [erl_parse:abstract_expr()]
86                 Indent = integer()
87                 Options = options()
88
89              Same as form/1,2, but only for the sequence  of  expressions  in
90              Expressions.
91
92       form(Form) -> io_lib:chars()
93
94       form(Form, Options) -> io_lib:chars()
95
96              Types:
97
98                 Form = erl_parse:abstract_form() | erl_parse:form_info()
99                 Options = options()
100
101              Pretty  prints  a Form, which is an abstract form of a type that
102              is returned by erl_parse:parse_form/1.
103
104       function(Function) -> io_lib:chars()
105
106       function(Function, Options) -> io_lib:chars()
107
108              Types:
109
110                 Function = erl_parse:abstract_form()
111                 Options = options()
112
113              Same as form/1,2, but only for function Function.
114
115       guard(Guard) -> io_lib:chars()
116
117       guard(Guard, Options) -> io_lib:chars()
118
119              Types:
120
121                 Guard = [erl_parse:abstract_expr()]
122                 Options = options()
123
124              Same as form/1,2, but only for the guard test Guard.
125

KNOWN LIMITATIONS

127       It is not possible to have hook functions for unknown  forms  at  other
128       places than expressions.
129

SEE ALSO

131       erl_eval(3), erl_parse(3), io(3)
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135Ericsson AB                       stdlib 3.10                        erl_pp(3)