+Input and Output in The Racket Guide introduces Ports and I/O.
13.1Ports
13.1.1Encodings and Locales
13.1.2Managing Ports
13.1.3Port Buffers and Positions
13.1.4Counting Positions, Lines, and Columns
13.1.5File Ports
13.1.6String Ports
13.1.7Pipes
13.1.8Structures as Ports
13.1.9Custom Ports
13.1.10More Port Constructors, Procedures, and Events
13.1.10.1Port String and List Conversions
13.1.10.2Creating Ports
13.1.10.3Port Events
13.1.10.4Copying Streams
13.2Byte and String Input
13.3Byte and String Output
13.4Reading
13.5Writing
13.6Pretty Printing
13.6.1Basic Pretty-Print Options
13.6.2Per-Symbol Special Printing
13.6.3Line-Output Hook
13.6.4Value Output Hook
13.6.5Additional Custom-Output Support
13.7Reader Extension
13.7.1Readtables
13.7.2Reader-Extension Procedures
13.7.3Special Comments
13.8Printer Extension
13.9Serialization
13.9.1Serialization Structures
13.10Fast-Load Serialization
13.11Cryptographic Hashing
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