mid

Builtin index · Collections & strings

result = substr(s, start, [length])

Input: s, start, length · Output: result

What it is

s is a Str; start (number, 0-based character index, must lie in [0, char_count]) is where the slice begins; optional length (number of characters, default: to the end) is clamped rather than erroring if it runs past what's left. Plain aliases of the same implementation (mid exists purely for BASIC/Excel discoverability).

Overloads

One call shape — this function is not overloaded.

Examples

From the documentation, and run by the build -- the output and the figure below are what the engine actually produced. Simplest first.

s = "Hello, World!"
print(substr(s, 7))          # "World!" — to the end

print(substr(s, 0, 5))       # "Hello" — bounded

print(substr(s, 7, 100))     # "World!" — clamped, not an error

print(mid(s, 7, 5))          # "World" — mid is substr under another name

World!
Hello
World!
World

from collections-strings

s = "Hello, Qu World!"
print(mid(s, 7, 2))          # "Qu"

print(left(s, 5))            # "Hello"

print(right(s, 6))           # "World!"

print(reverse("abc"))        # "cba"

print(lower("SHOUT"))        # "shout"

print(ucase("shout"))        # "SHOUT"

print(lcase("SHOUT"))        # "shout"

print(toupper("mix"))        # "MIX"

print(tolower("MIX"))        # "mix"

print(capitalize("ada lovelace"))  # "Ada lovelace"

print(ltrim("   padded"))    # "padded"

print(rtrim("padded   ") + "|")   # "padded|"

print(pad_right("ab", 5, "."))    # "ab..."

print(compare("apple", "banana")) # -1

print(asc("A"))              # 65

Qu
Hello
World!
cba
shout
SHOUT
shout
MIX
mix
Ada lovelace
padded
padded|
ab...
-1
    ... 1 more lines

from collections-strings

How it works

All index/length arguments below are 0-based (matching every other index in this codebase) and unicode-aware: built on .chars(), never a raw byte slice, so a multi-byte UTF-8 string indexes by character, not by byte (a naive byte slice would panic or corrupt on non-ASCII input). substr(s, start[, length]) / mid(s, start, length) — plain aliases of the same implementation: MATLAB has no mid at all (that's a BASIC/Excel convention), and since Qu already indexes 0-based everywhere (unlike BASIC/Excel's 1-based MID$), there is no real semantic difference to preserve — mid exists purely for discoverability by BASIC/Excel habit. start must be within [0, char_count] (== char_count is the valid "nothing left" case, matching the empty-slice-at-the-end convention s[n:] uses elsewhere); length is clamped to whatever is actually available rather than erroring — asking for more than what's left (substr(s, 0, 1000) to mean "the rest") is a common, harmless overshoot, unlike a genuinely out-of-range start.

From the note above this builtin in the interpreter, where the reasoning was written down as it was built.

See also

substr — documented in the same entry.