Strings

String

Strings in Seen are UTF-8 encoded, represented as {len: Int, data: ptr}.

String Interpolation

let name = "World"
println("Hello, {name}!")
println("2 + 2 = {2 + 2}")

Operators

let greeting = "Hello, " + "World!"     // concatenation
let equal = "abc" == "abc"              // equality
let notEqual = "abc" != "xyz"           // inequality

Length

let s = "hello"
let len = s.length()           // byte length: 5

Character Access

let ch = seen_char_at(s, 0)   // Unicode code point at index
let byte = seen_byte_at(s, 0) // raw byte at index

String Functions

Prefix, suffix, search, count, split, and replace helpers scan byte indexes directly and allocate only the returned pieces or rebuilt result. Common prefix/suffix and substring probes use runtime byte-search fast paths, including a single-byte memchr path for delimiter-heavy workloads.

Function	Signature	Description
split	(text: String, delimiter: String) r: Array<String>	Split by delimiter
trim	(text: String) r: String	Remove leading/trailing whitespace
startsWith	(text: String, prefix: String) r: Bool	Check prefix
endsWith	(text: String, suffix: String) r: Bool	Check suffix
contains	(text: String, needle: String) r: Bool	Check substring
indexOf	(text: String, needle: String, start: Int) r: Int	Find first occurrence (-1 if not found)

Runtime String Functions

Function	Signature	Description
seen_str_concat_ss	(a: String, b: String) r: String	Concatenate
seen_str_eq_ss	(a: String, b: String) r: Bool	Equality
seen_substring	(s: String, start: Int, end: Int) r: String	Substring extraction
seen_int_to_string	(n: Int) r: String	Int to string
seen_float_to_string	(f: Float) r: String	Float to string
seen_char_to_str	(c: Int) r: String	Char code point to string

Stdlib String Functions

Function	Signature	Description
String_toUpperCase	(s: String) r: String	Uppercase conversion
String_toLowerCase	(s: String) r: String	Lowercase conversion
String_toInt	(s: String) r: Int	Parse as integer
String_toFloat	(s: String) r: Float	Parse as float
String_reverse	(s: String) r: String	Reverse string
String_isEmpty	(s: String) r: Int	Check if empty
String_count	(s: String, needle: String) r: Int	Count occurrences
String_replace	(s: String, old: String, new: String) r: String	Replace all occurrences
String_fromCharCode	(code: Int) r: String	Create from Unicode code point

Extended String Functions (seen_std/src/str/)

Function	Signature	Description
trimStart	(s: String) r: String	Trim leading whitespace
trimEnd	(s: String) r: String	Trim trailing whitespace
lastIndexOf	(s: String, needle: String) r: Int	Last occurrence
lines	(s: String) r: Array<String>	Split into lines
splitWhitespace	(s: String) r: Array<String>	Split on whitespace
words	(s: String) r: Array<String>	Split into words
replaceFirst	(s: String, old: String, new: String) r: String	Replace first occurrence
removePrefix	(s: String, prefix: String) r: String	Remove prefix if present
removeSuffix	(s: String, suffix: String) r: String	Remove suffix if present
ensurePrefix	(s: String, prefix: String) r: String	Add prefix if missing
ensureSuffix	(s: String, suffix: String) r: String	Add suffix if missing
padStart	(s: String, len: Int, ch: Char) r: String	Pad start
padEnd	(s: String, len: Int, ch: Char) r: String	Pad end
repeat	(s: String, n: Int) r: String	Repeat N times
join	(arr: Array<String>, sep: String) r: String	Join with separator

StringBuilder

Efficient string building with amortized allocation. repeat, join, split, and compiler-facing builder paths use this instead of repeated string concatenation for large outputs. toString() flattens the accumulated parts through a one-pass runtime helper.

import str.string

Constructor

let sb = StringBuilder.new()

Methods

Method	Return	Description
append(text: String)	Void	Append string
tryAppend(text: String)	Result<Unit, AllocError>	Append after checking the current memory budget
appendChar(ch: Char)	Void	Append character
appendLine(text: String)	Void	Append string + newline
appendAll(values: Array<String>)	Void	Append all strings
clear()	Void	Clear contents
isEmpty()	Bool	Check if empty
length()	Int	Get total length
toString()	String	Build final string with a linear flatten pass
tryToString()	Result<String, AllocError>	Build after checking the current memory budget
writeToFile(path: String)	Bool	Stream builder parts to a file
buildAndClear()	String	Build string and clear builder

Example

let sb = StringBuilder.new()
sb.append("Hello")
sb.append(", ")
sb.append("World!")
let result = sb.toString()  // "Hello, World!"

Character Functions

Function	Signature	Description
Char_isDigit	(c: Int) r: Int	Is digit [0-9]
Char_isAlpha	(c: Int) r: Int	Is alphabetic [A-Za-z]
Char_isAlphanumeric	(c: Int) r: Int	Is alphanumeric
Char_isUpperCase	(c: Int) r: Int	Is uppercase
Char_isLowerCase	(c: Int) r: Int	Is lowercase
Char_isWhitespace	(c: Int) r: Int	Is whitespace
Char_toUpperCase	(c: Int) r: Int	To uppercase
Char_toLowerCase	(c: Int) r: Int	To lowercase
Char_toInt	(c: Int) r: Int	Character to integer (identity)