String Transforms

Scalar string operations. Lift with .map to apply to an array of strings.

Case

Method	What	Example
`upper`	ASCII uppercase	`"foo".upper()` → `"FOO"`
`lower`	ASCII lowercase	`"FOO".lower()` → `"foo"`
`capitalize`	First char upper, rest lower	`"foo bar".capitalize()` → `"Foo bar"`
`title_case`	Each word capitalised	`"foo bar".title_case()` → `"Foo Bar"`
`snake_case`	`lowerSnake_case` to `lower_snake_case`	`"FooBar".snake_case()` → `"foo_bar"`
`kebab_case`	Words joined with `-`	`"FooBar".kebab_case()` → `"foo-bar"`
`camel_case`	`fooBar` style	`"foo_bar".camel_case()` → `"fooBar"`
`pascal_case`	`FooBar` style	`"foo_bar".pascal_case()` → `"FooBar"`
`reverse_str`	Reverse char order	`"abc".reverse_str()` → `"cba"`

Trim

Method	What
`trim`	Strip whitespace from both ends
`trim_left`	Strip leading whitespace
`trim_right`	Strip trailing whitespace

QUERY:  "  hi  ".trim()     OUT: "hi"
QUERY:  "  hi  ".trim_left()     OUT: "hi  "

Padding and centering

Method	Signature	Example
`pad_left(width, char?)`	Right-align by padding left	`"7".pad_left(3, "0")` → `"007"`
`pad_right(width, char?)`	Left-align by padding right	`"hi".pad_right(5)` → `"hi "`
`center(width, char?)`	Center within width	`"hi".center(6)` → `" hi "`

If char is omitted, space is used.

Indent / dedent

indent(n) takes an integer (number of spaces); the prefix is fixed spaces.

QUERY:  "line1\nline2".indent(2)
OUT:    "  line1\n  line2"

dedent() strips the first line's leading whitespace from every subsequent line that begins with the same prefix. It is not a common-prefix dedent across all lines:

QUERY:  "  a\n  b".dedent()
OUT:    "a\nb"

Slice

"hello world".slice(0, 5)      # "hello"
"hello world".slice(6)         # "world"
"hello".slice(-3)              # "llo"

slice(start, end?) mirrors Python; end is exclusive.

Repeat

"ab".repeat(3)        # "ababab"

Replace

Method	Behavior
`replace(needle, with)`	Replace first literal occurrence
`replace_all(needle, with)`	Replace all literal occurrences
`replace_re(pattern, with)`	Regex-aware single replacement
`replace_all_re(pattern, with)`	Regex-aware all replacements

QUERY:  "hello hello".replace("hello", "hi")
OUT:    ["hi hello"]

QUERY:  "hello hello".replace_all("hello", "hi")
OUT:    ["hi hi"]

QUERY:  "abc123def".replace_all_re("\d+", "#")
OUT:    "abc#def"

Regex escapes inside jetro string literals. Use a single backslash: "\d", "\w+", "\s". Jetro string literals don't eat backslashes separately; doubling ("\\d") sends the regex engine the literal two-char sequence \\d, which is not the digit class and silently fails to match. This differs from host languages like Python or JavaScript where you must double-escape.

Strip

"prefix-foo".strip_prefix("prefix-")  # "foo"
"foo.txt".strip_suffix(".txt")        # "foo"

If the prefix/suffix isn't present, returns the input unchanged.

Encoding

Method	What
`to_base64`	Standard base64 encode
`from_base64`	Standard base64 decode
`url_encode`	Percent-encode
`url_decode`	Percent-decode
`html_escape`	`&` → `&`, `<` → `<`, etc.
`html_unescape`	Reverse of `html_escape`

QUERY:  "hello world".to_base64()     OUT: "aGVsbG8gd29ybGQ="
QUERY:  "a b".url_encode()     OUT: "a%20b"
QUERY:  "<b>".html_escape()     OUT: "&lt;b&gt;"

Demand notes

All string transforms are Identity demand-wise: they don't change what the upstream needs to produce.

Practical examples

# Normalise display names
$.users.map(u => u.name.trim().title_case().first())

# Build an URL-safe slug
"My Article Title".lower().replace_all(" ", "-")
# → "my-article-title"

# CamelCase to snake_case migration
"FooBarBaz".snake_case()                # → "foo_bar_baz"

# Truncate with ellipsis
$.posts.map(p => p.body.slice(0, 100) + "..." if p.body.len() > 100 else p.body)

# Parse a comma-separated tag list
$.tags_csv.split(",").map(@.trim())

# Encode for URL
$.query.url_encode()

# Encode binary as base64
$.bytes.to_base64()

# HTML-escape user input
$.comments.map(c => c.text.html_escape())

# Pad a numeric ID for fixed-width keys
($.id as string).pad_left(8, "0")
# → "00000042" for id=42

# Strip a known prefix
"https://example.com/path".strip_prefix("https://")
# → "example.com/path"

# Build a banner
"=".repeat(40)                          # → "========================================"

# Indent a nested message
$.message.indent(4)

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