Reading Input

Reading Input

Thagore provides built-in and standard library functions for reading from stdin. The built-in input() function reads a line from the console, and the io module adds prompts and bulk-read helpers.

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Built-in: input()

The input() function is a language built-in — no import needed. It reads one line from standard input and returns it as a String. The trailing newline is stripped automatically.

hello_input.tg

func main() -> i32:
    print("What is your name?")
    let name = input()
    print("Hello, " + name + "!")
    return 0

What is your name?
> Minh
Hello, Minh!

Note

input() returns an empty string "" on EOF (e.g. piped input that has ended) — it never returns null.

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Built-in: input() with i32 parse

To read an integer, read the string first then parse with str.parse_i32(), or use io.input_i32() from the io module:

read_number.tg

import "lib/io.tg" as io

func main() -> i32:
    print("Enter a number:")
    let n = io.input_i32()
    print(n * 2)
    return 0

Enter a number:
> 21
42

Legacy built-in

In older Stage1 code you may see the bare input() call being used as an i32 — this is the original Stage1 codegen behaviour where input() compiled directly to @__thg_input_i32(). In modern code, use io.input_i32() for clarity.

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io Module Functions

Import the io module for all input helpers:

import "lib/io.tg" as io

Function Reference

Function	Return	Description
io.input_prompt(prompt)	String	Print a prompt then read a line from stdin
io.input_prompt()	String	Read a line with no prompt (same as input())
io.input_i32()	i32	Read a line and parse it as a signed integer
io.stdin_read_line(prompt)	String	Alias for input_prompt
io.stdin_read_all()	String	Read entire stdin into a single string
io.stdread(path)	String	Read from a file or from stdin if path is "", "-", or "stdin"

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io.input_prompt() — Prompt + Read

Shows a prompt on the same line, then waits for input:

greet.tg

import "lib/io.tg" as io
import "lib/string.tg" as str

func main() -> i32:
    let name = str.trim(io.input_prompt("Enter your name: "))
    let age_s = str.trim(io.input_prompt("Enter your age: "))
    print("Hello " + name + "! You entered age: " + age_s)
    return 0

Enter your name: Minh
Enter your age: 22
Hello Minh! You entered age: 22

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io.stdin_read_all() — Read All of Stdin

Reads everything from stdin into a single String. Useful when piping input into a program:

echo_all.tg

import "lib/io.tg" as io

func main() -> i32:
    let text = io.stdin_read_all()
    print("You sent " + text)
    return 0

echo "hello world" | ./echo_all
# You sent hello world

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io.stdread() — File or Stdin

stdread(path) reads from a file path, or from stdin if the path is one of the standard stdin selectors:

Path value	Behaviour
"" (empty string)	reads stdin
"-"	reads stdin
"stdin" / "STDIN"	reads stdin
"con" / "CON"	reads stdin (Windows console)
"/dev/stdin"	reads stdin
any other path	reads that file

cat.tg

import "lib/io.tg" as io
import "lib/env.tg" as env

func main() -> i32:
    let path = env.get(1)
    let text = io.stdread(path)
    print(text)
    return 0

./cat myfile.txt      # reads myfile.txt
./cat -               # reads stdin
./cat                 # reads stdin (empty path)

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Reading Multiple Lines (Loop)

Use a loop with input() to read until EOF:

sum_lines.tg

import "lib/string.tg" as str

func main() -> i32:
    let total = 0
    let line = input()
    while (str.len(line) > 0):
        let n = str.parse_i32(line)
        total = total + n
        line = input()
    print(total)
    return 0

printf "10\n20\n30\n" | ./sum_lines
# 60

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Practical Example: Simple Calculator

calc.tg

import "lib/io.tg" as io
import "lib/string.tg" as str

func main() -> i32:
    let a = str.parse_i32(str.trim(io.input_prompt("First number:  ")))
    let b = str.parse_i32(str.trim(io.input_prompt("Second number: ")))
    print("Sum:      " + str.from_i32(a + b))
    print("Diff:     " + str.from_i32(a - b))
    print("Product:  " + str.from_i32(a * b))
    return 0

First number:  10
Second number: 3
Sum:      13
Diff:     7
Product:  30

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Summary

Use case	Code
Read a string line (no prompt)	let s = input()
Read a string with prompt	let s = io.input_prompt("Enter: ")
Read an integer	let n = io.input_i32()
Read all of stdin	let text = io.stdin_read_all()
Read file or stdin	let text = io.stdread(path)

Next Steps

• Print & Output — the counterpart to input
• Strings — str.trim(), str.parse_i32(), str.from_i32()
• Standard I/O modules — full io module reference