[pmarin]. ReadChar is an implementation of the classic getc and putbak functions. <<br>>
For more info see the page 255 of Software Tools by Kernighan and Plauger. <<br>>
The code is part of [Muddy Scheme]
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======
package require TclOO
package require struct::stack

oo::class create ReadChar {

        constructor {{chan stdin}} {
                my variable ch 
                my variable buf
                set ch $chan
                set buf [struct::stack]
        }
        
        method getc {} {
                my variable ch
                my variable buf
                if  {[$buf size]} {
                        return [$buf pop]
                } else {
                        if {![eof $ch]} {
                                return [read $ch 1] 
                        } else {
                                return "eof"        
                        }
                }
        }
        
        method eof {} {
                my variable ch
                my variable buf
                if { ![$buf size] && [eof $ch] } {
                        return 1 
                } else {
                        return 0 
                }
        }
        
        method peek {} {
                my variable ch 
                my variable buf

                if  {[$buf size]} {
                        return [$buf peek]
                } else {
                        if {![eof $ch]} {
                                set c [read $ch 1]
                                $buf push $c 
                                return $c
                        } else {
                                return "eof"        
                        }
                }

        }

        method putbak str {
                my variable buf
                if { [string length $str] > 0 } {
                        if { [string length $str] == 1 } {
                                $buf push $str
                        } else {
                                foreach i [split [string reverse $str] {}] {
                                        $buf push $i        
                                }
                        }
                }
        }

        destructor  {
                my variable ch 
                my variable buf
                $buf destroy
                close $ch
        }
}
======

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**Coments**
It is rare that It is not already implemented in the core libraries... Am I missing something?

DCP: Never ever needed to read or write a single char in Tcl in the last 10-15 years! <<br>>
[pmarin] Even the C Standartd Library comes whith getc and ungetc (stdio.h)!