WIP

format.red

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+Red [
+    Title:  "String formatting, similar to Python's format()" 
+    Author: "Galen Ivanov"
+
+]
+
+
+; alignment: left / right / center ; width x trim ; [padding]
+; thousand separator:  
+; fix point 
+
+; base conversions
+; decimal
+; scientific format e/E
+; percentage
+; dates: ddmmyyyy ddmmmyyyy yyyymmdd yyyyddd yyyyw 
+
+
+context [
+
+    left: function[
+        {Left aligns the text, truncated to amount/y chars (0 means no change).
+        Pads to amount/x chars to the right using fill} 
+        text   
+        amount [pair!]
+        fill   [char!]
+    ][
+        text: form text
+        if zero? amount/y[amount/y: length? text]
+        pad/with take/part text amount/y amount/x fill
+    ]
+
+    right: function[
+        {Right aligns the text, truncated to amount/y chars (means is no change).
+        Pads to amount/x chars to the left using fill} 
+        text  
+        amount [pair!]
+        fill   [char!]
+    ][
+        text: form text
+        if zero? amount/y[amount/y: length? text]
+        pad/left/with take/part text amount/y amount/x fill
+    ]
+
+    center: function[
+        {Centers the text, truncated to amount/y chars (0 means no change).
+        Pads to amount/x chars to the left and right using fill} 
+        text   
+        amount [pair!]
+        fill   [char!]
+    ][
+        text: form text
+        if zero? amount/y[amount/y: length? text]
+        text: take/part text amount/y
+        c-text: pad/left/with copy text amount/x fill
+        d: to 1 amount/x - (length? text) / 2
+        move/part c-text tail c-text  d
+    ]
+
+    sep: function[
+        {Places a thousand separator dlm in number's integer part
+        and left aligns the result padded to amount characters with fill}
+        num    [number!]
+        amount [integer!]
+        dlm    [char!]
+        fill   [char!]
+    ][
+        d: charset "0123456789"
+        num: form num
+        rev-num: reverse num
+        rev-num: any [find/tail rev-num "." rev-num]
+        parse rev-num [any[3 d ahead d insert dlm]]
+        pad/left/with reverse num amount fill
+        num
+    ]
+
+    fixed: function[
+        num    [number!]
+        amount [pair!]
+        fill   [char!]
+    ][
+        frac: 1.0 / (10 ** amount/y)
+        num: round/to num frac
+        set[i f]split form num "."
+        pad/left/with rejoin[i "." pad/with f amount/y #"0"] amount/x fill
+    ]
+
+
+    fmt: function[
+        spec [string!]
+        vals [block!]
+    ][
+        padding: space
+        key: ""
+        parse spec[copy key to[end | ["|" copy cmd to end (cmd: load cmd)]]]
+        key: select vals to set-word! load key
+
+        key: switch cmd/1 [
+            left   [left   key cmd/2 any[cmd/3 padding]]
+            right  [right  key cmd/2 any[cmd/3 padding]]
+            center [center key cmd/2 any[cmd/3 padding]]
+            sep    [sep    key cmd/2 any[cmd/3 #"'"] any[cmd/4 padding]]
+            fixed  [fixed  key cmd/2 any[cmd/3 padding]]
+        ]
+        key
+    ]
+
+
+    set 'format function[
+        {Simple string formatting using a block of keyword parameters}
+        str [string!] "String to format" 
+        vals [block!]  "A block with set-word - value pairs"
+    ][
+        parse str[
+            any[
+                to remove "{" 
+                change copy subs to remove "}" (fmt subs vals)
+            ]
+        ]
+        str    
+    ]
+]
+
+;tests
+print format {My name is {name|left 10x0 #"_"}. I'm {age | fixed 7x2} years old.}[age: 36,345 name: "John"]
+print format {The price is USD {price|sep 15 #"," #"-"}.}[price: 1234502342.67]