Text Pipeline - Swift Programming

A text pipeline keeps lines with a chosen prefix and joins the result.

Filter lines by prefix

prefix prefix = "TODO" (default)prefix = "DONE"prefix = "NOTE"

text_pipeline.swift

Replay: real traced execution (multi-file project)

let prefix = "TODO"
let lines = [
    "TODO write outline",
    "DONE review draft",
    "TODO publish page"
]
var matches: [String] = []

for line in lines {
    if line.hasPrefix(prefix) {
        matches.append(line)
    }
}

let output = matches.joined(separator: " | ")

print(output)

let prefix = "DONE"
let lines = [
    "TODO write outline",
    "DONE review draft",
    "TODO publish page"
]
var matches: [String] = []

for line in lines {
    if line.hasPrefix(prefix) {
        matches.append(line)
    }
}

let output = matches.joined(separator: " | ")

print(output)

let prefix = "NOTE"
let lines = [
    "TODO write outline",
    "DONE review draft",
    "TODO publish page"
]
var matches: [String] = []

for line in lines {
    if line.hasPrefix(prefix) {
        matches.append(line)
    }
}

let output = matches.joined(separator: " | ")

print(output)

prefix ← TODO, lines ← ["TODO write outline", "DONE review draft", "TODO publish page"]

1let prefix→ TODO = "TODO"  //@prefix="DONE", "NOTE"2let lines→ ["TODO write outline", "DONE review draft", "TODO publish page"] = [3    "TODO write outline",4    "DONE review draft",5    "TODO publish page"6]7var matches→ []: [String] = []⋯

2
for line in lines
pass 1 of 3
```
⋯9for lineTODO write outline in lines["TODO write outline", "DONE review draft", "TODO publish page"] {10    if line.hasPrefix(prefix) {⋯
```
All 3 passes — pass 1 is the card above
pass line prefix matches
1 TODO write outline TODO []
2 DONE review draft — —
3 TODO publish page TODO ["TODO write outline"]

All 3 passes — pass 1 is the card above
pass	`line`	`prefix`	`matches`
1	TODO write outline	TODO	[]
2	DONE review draft	—	—
3	TODO publish page	TODO	["TODO write outline"]

if line.hasPrefix(prefix)

pass 1 of 2

⋯9for line in lines {10    if lineTODO write outline.hasPrefix(prefixTODO) {11        matches[].append(lineTODO write outline)12    }⋯

if line.hasPrefix(prefix)

pass 2 of 2

⋯9for line in lines {10    if lineTODO publish page.hasPrefix(prefixTODO) {11        matches["TODO write outline"].append(lineTODO publish page)12    }⋯

output ← TODO write outline | TODO publish page

⋯15let output→ TODO write outline | TODO publish page = matches["TODO write outline", "TODO publish page"].joined(separator: " | ")1617print(outputTODO write outline | TODO publish page)⋯

outputTODO write outline | TODO publish page

prefix ← DONE, lines ← ["TODO write outline", "DONE review draft", "TODO publish page"]

1let prefix→ DONE = "DONE"2let lines→ ["TODO write outline", "DONE review draft", "TODO publish page"] = [3    "TODO write outline",4    "DONE review draft",5    "TODO publish page"6]7var matches→ []: [String] = []⋯

2
for line in lines
pass 1 of 3
```
⋯9for lineTODO write outline in lines["TODO write outline", "DONE review draft", "TODO publish page"] {10    if line.hasPrefix(prefix) {⋯
```
All 3 passes — pass 1 is the card above
pass line prefix matches
1 TODO write outline — —
2 DONE review draft DONE []
3 TODO publish page — —

All 3 passes — pass 1 is the card above
pass	`line`	`prefix`	`matches`
1	TODO write outline	—	—
2	DONE review draft	DONE	[]
3	TODO publish page	—	—

if line.hasPrefix(prefix)

⋯9for line in lines {10    if lineDONE review draft.hasPrefix(prefixDONE) {11        matches[].append(lineDONE review draft)12    }⋯

output ← DONE review draft

⋯15let output→ DONE review draft = matches["DONE review draft"].joined(separator: " | ")1617print(outputDONE review draft)⋯

outputDONE review draft

prefix ← NOTE, lines ← ["TODO write outline", "DONE review draft", "TODO publish page"]

1let prefix→ NOTE = "NOTE"2let lines→ ["TODO write outline", "DONE review draft", "TODO publish page"] = [3    "TODO write outline",4    "DONE review draft",5    "TODO publish page"6]7var matches→ []: [String] = []⋯

for line in lines

pass 1 of 3

⋯9for lineTODO write outline in lines["TODO write outline", "DONE review draft", "TODO publish page"] {10    if line.hasPrefix(prefix) {⋯

All 3 passes — pass 1 is the card above
pass	`line`
1	TODO write outline
2	DONE review draft
3	TODO publish page

output ← (empty)

⋯15let output→ (empty) = matches[].joined(separator: " | ")1617print(output(empty))⋯

text pipeline Small text tools often run a sequence of steps: read lines, filter them, then format the result.